unstable temp measurement
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Posts: 46,084
I am using a basic stamp 2 with an AD831 and an LM35 temp probe. The circuit is
out of "The microcontroller application cookbook" and the circuit works fine
sometimes but sometimes I am troubled by shifting, unstable temp measurments.
The LM 35 has tested good out of the circuit but in the circuit its value hopps
around several degrees celsius, even though I use a loop in the code to average
the reading over 1 sec.
Does anybody have expereince with this application??
Uwe
out of "The microcontroller application cookbook" and the circuit works fine
sometimes but sometimes I am troubled by shifting, unstable temp measurments.
The LM 35 has tested good out of the circuit but in the circuit its value hopps
around several degrees celsius, even though I use a loop in the code to average
the reading over 1 sec.
Does anybody have expereince with this application??
Uwe
Comments
othello159@h... writes:
> I am using a basic stamp 2 with an AD831 and an LM35 temp probe. The
> circuit is out of "The microcontroller application cookbook" and the circuit
works
> fine sometimes but sometimes I am troubled by shifting, unstable temp
> measurments. The LM 35 has tested good out of the circuit but in the circuit
its
> value hopps around several degrees celsius, even though I use a loop in the
> code to average the reading over 1 sec.
>
> Does anybody have expereince with this application??
>
Two things - use a .1uf bypass right at your ADC input pin, and put a 1K
resistor in series with the sensing lead from your sensor. This will improve
stability tremendously.
Sid Weaver
Always thinking.....
http://www.visualmuses.com/chipcircuit/index.html
[noparse][[/noparse]Non-text portions of this message have been removed]
> In a message dated 4/19/2004 10:52:59 AM Eastern Daylight Time,
> othello159@h... writes:
>
>
> > I am using a basic stamp 2 with an AD831 and an LM35 temp probe.
The
> > circuit is out of "The microcontroller application cookbook" and
the circuit works
> > fine sometimes but sometimes I am troubled by shifting, unstable
temp
> > measurments. The LM 35 has tested good out of the circuit but in
the circuit its
> > value hopps around several degrees celsius, even though I use a
loop in the
> > code to average the reading over 1 sec.
> >
> > Does anybody have expereince with this application??
> >
>
> Two things - use a .1uf bypass right at your ADC input pin, and
put a 1K
> resistor in series with the sensing lead from your sensor. This
will improve
> stability tremendously.
>
> Sid Weaver
> Always thinking.....
> http://www.visualmuses.com/chipcircuit/index.html
>
>
>
>
>
> [noparse][[/noparse]Non-text portions of this message have been removed]
Sid,
Hope you can answer this for me. I am new to Stamps and am having a
similar situation as othello159, except mine was with the LM34 and
unstable measurements. I was hoping you could explain what the
resistor and capacitor are actually doing to make the readings more
accurate.
speakman@o... writes:
> Hope you can answer this for me. I am new to Stamps and am having a
> similar situation as othello159, except mine was with the LM34 and
> unstable measurements. I was hoping you could explain what the
> resistor and capacitor are actually doing to make the readings more
> accurate.
>
We use LM34 sensor exclusively in all of our projects. The capacitor gets
rid of noise on the ADC input. The resistor and the capacitor also form a
rather complicated RC network, which was explained to me but I don't really
understand. All I really know is that it works.
Sid Weaver
Always thinking.....
http://www.visualmuses.com/chipcircuit/index.html
[noparse][[/noparse]Non-text portions of this message have been removed]
influences, it is self-oscillation of the LM34 chip. Micropower
circuits like the LM34 have a limited capability to drive capacitive
loads, like a cable. The same thing is true of low-power operational
amplifiers, like the LM358.
External capacitance gives a phase shift that is just right to make
the circuit break into a small oscillation. If you hook the output
of the LM34 directly to an oscilloscope on a ~5mV/div AC range, the
display will be pretty solide. But if you stick on a cable in the
neighborhood of 2 feet to 30 feet, you will see an oscillation of as
much as 30 millivolts, which is equivalent to 3 degrees. Depending
on your ADC, that will come out as an error of some sort, even when
you average it.
Micropower op amps also have trouble when a capacitor is suddenly
attached to their output, as happens when your read the temperature
with a switched capacitor ADC like the TLC2543. To sample its
inputs, the ADC suddenly attaches the sampling capacitor to the input
to collect a sample of the input voltage, and then detaches that
capacitor to move the sample on into the conversion process. For a
micropower circuit like the LM34 or an LM358 op amp, that sudden
change of capacitance is like hitting the output with a sledge
hammer, and the circuit rings like a bell.
The extra small resistor and capacitor on the output act as "leading"
compensation. You can look at it this way. The current into the
capacitor has to flow through the resistor. The voltage across the
resistor is proportional to the current, and adds to the voltage
across the capacitor. The current "predicts" or leads the voltage,
and that is what gets fed back to the input of the op amp inside the
LM34. In terms of phase, that "leading" compensates for the "lag"
caused by the open loop resistance of the op-amp. The circuit never
reaches the point where it goes into oscillation.
The LM34 data sheet explains a lot of this.
-- regards,
Tracy
>In a message dated 4/19/2004 12:11:04 PM Eastern Daylight Time,
>speakman@o... writes:
>
>
>> Hope you can answer this for me. I am new to Stamps and am having a
>> similar situation as othello159, except mine was with the LM34 and
>> unstable measurements. I was hoping you could explain what the
>> resistor and capacitor are actually doing to make the readings more
>> accurate.
>>
>
>We use LM34 sensor exclusively in all of our projects. The capacitor gets
>rid of noise on the ADC input. The resistor and the capacitor also form a
>rather complicated RC network, which was explained to me but I don't really
>understand. All I really know is that it works.
>
>Sid Weaver
>Always thinking.....
>http://www.visualmuses.com/chipcircuit/index.html
>
>
> --- In basicstamps@yahoogroups.com, Newzed@a... wrote:
> > In a message dated 4/19/2004 10:52:59 AM Eastern Daylight Time,
> > othello159@h... writes:
> >
> >
> > > I am using a basic stamp 2 with an AD831 and an LM35 temp
probe.
> The
> > > circuit is out of "The microcontroller application cookbook"
and
> the circuit works
> > > fine sometimes but sometimes I am troubled by shifting,
unstable
> temp
> > > measurments. The LM 35 has tested good out of the circuit but
in
> the circuit its
> > > value hopps around several degrees celsius, even though I use a
> loop in the
> > > code to average the reading over 1 sec.
> > >
> > > Does anybody have expereince with this application??
> > >
> >
> > Two things - use a .1uf bypass right at your ADC input pin, and
> put a 1K
> > resistor in series with the sensing lead from your sensor. This
> will improve
> > stability tremendously.
> >
> > Sid Weaver
> > Always thinking.....
> > http://www.visualmuses.com/chipcircuit/index.html
> >
> >
> >
> >
> >
> > [noparse][[/noparse]Non-text portions of this message have been removed]
>
>
> Sid,
>
> Hope you can answer this for me. I am new to Stamps and am having a
> similar situation as othello159, except mine was with the LM34 and
> unstable measurements. I was hoping you could explain what the
> resistor and capacitor are actually doing to make the readings more
> accurate.
google 'passive filter' or 'RC filter' for lots of details on how the
RC filter works.
Most simply put, the capacitor resists changes in the signal so it
makes the reading steady.
Dave
Making things faster and easier
http://www.visualmuses.com/chipcircuit/index.html
I went and got the data sheet to read up on this, it seemed they want the bypass
capacitors at the sensor, not so much at the end of the cable and closer to the
AD chip.
But anyways, I experimented with a few set ups on my bench and also stuck, as
Tracy had suggested, just the LM35 on my scope and indeed, there was some ripple
and hash with surprisingly high frequency, several MHZ.
But I could not get the readings to stabilize until I followed a hunch and
changed power supplies, from a big HP 6433B bench supply to a little shitty $7
Jameco surplus switching supply and bingo, everything stabilized right there.
The scope shows isolated 50mV burst among the ripple of the HP, I don't know
what all this means yet but I sure know where these problems suddenly came from,
I apparently introduced them through the supply voltage myself.
I hope this is the end of it...
73 Uwe
--- In basicstamps@yahoogroups.com, Tracy Allen <tracy@e...> wrote:
> The problem is not so much noise, in the sense of external
> influences, it is self-oscillation of the LM34 chip. Micropower
> circuits like the LM34 have a limited capability to drive capacitive
> loads, like a cable. The same thing is true of low-power operational
> amplifiers, like the LM358.
>
> External capacitance gives a phase shift that is just right to make
> the circuit break into a small oscillation. If you hook the output
> of the LM34 directly to an oscilloscope on a ~5mV/div AC range, the
> display will be pretty solide. But if you stick on a cable in the
> neighborhood of 2 feet to 30 feet, you will see an oscillation of as
> much as 30 millivolts, which is equivalent to 3 degrees. Depending
> on your ADC, that will come out as an error of some sort, even when
> you average it.
>
> Micropower op amps also have trouble when a capacitor is suddenly
> attached to their output, as happens when your read the temperature
> with a switched capacitor ADC like the TLC2543. To sample its
> inputs, the ADC suddenly attaches the sampling capacitor to the input
> to collect a sample of the input voltage, and then detaches that
> capacitor to move the sample on into the conversion process. For a
> micropower circuit like the LM34 or an LM358 op amp, that sudden
> change of capacitance is like hitting the output with a sledge
> hammer, and the circuit rings like a bell.
>
> The extra small resistor and capacitor on the output act as "leading"
> compensation. You can look at it this way. The current into the
> capacitor has to flow through the resistor. The voltage across the
> resistor is proportional to the current, and adds to the voltage
> across the capacitor. The current "predicts" or leads the voltage,
> and that is what gets fed back to the input of the op amp inside the
> LM34. In terms of phase, that "leading" compensates for the "lag"
> caused by the open loop resistance of the op-amp. The circuit never
> reaches the point where it goes into oscillation.
>
> The LM34 data sheet explains a lot of this.
>
> -- regards,
> Tracy
>
>
> >In a message dated 4/19/2004 12:11:04 PM Eastern Daylight Time,
> >speakman@o... writes:
> >
> >
> >> Hope you can answer this for me. I am new to Stamps and am having a
> >> similar situation as othello159, except mine was with the LM34 and
> >> unstable measurements. I was hoping you could explain what the
> >> resistor and capacitor are actually doing to make the readings more
> >> accurate.
> >>
> >
> >We use LM34 sensor exclusively in all of our projects. The capacitor gets
> >rid of noise on the ADC input. The resistor and the capacitor also form a
> >rather complicated RC network, which was explained to me but I don't really
> >understand. All I really know is that it works.
> >
> >Sid Weaver
> >Always thinking.....
> >http://www.visualmuses.com/chipcircuit/index.html
> >
> >
http://www.testelectronics.com/used/hp6433b.htm
Hewlett Packard 6433B
DC POWER SUPPLY
The 6433B Power Supply is a SCR based regulated supply which
provides good high current output capability but also outputs a slight
amount of ripple. Constant-Voltage/Constant-Current modes. DC output from
0-36V @ 0-10A. Large easy-to-read meters continuously monitor output voltage
and current. Bus bars and terminal blocks on the rear panel provide
connections for input and output power, remote sensing, remote programming,
and auto-series, parallel, and tracking connections. Unit also incorporates
reverse voltage protection and a fused AC input. Operates from 115 VAC ±10%,
single phase, 57-63 Hz.
Though it is not a classic switcher (in my mind), it's not a classic linear
supply. All supplies, not linear, are suspect of serious noise problems.
Good that you used a scope. I do almost all my troubleshooting on a scope.
I had an op amp one time that was oscillating at 425 MHz. It was not
obvious from lower quality instruments what the problem was<G>.
Why the inexpensive switcher was better? I haven't a clue. However, it may
be that you aren't really loading it much, and it only switches on a little
every now and then for charging. Load it to about 1/2 of full power and see
if it still puts out a clean signal.
Something else to remember. Switchers that I have used have been seriously
offended at non-constant loads. We used one on a good sized motorized dune
buggy when characterizing the motor. We couldn't get the controller
(digital proportional with digital control) to act right, and the power
supply kept changing Voltage on us. There was interaction between the
digital proportion circuits and the switcher.
Good luck.
Original Message
From: othello159 [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=55VW0wm8O41ZFVr6O7NEcUBN0ukGrGnfg_3fXfXNPZQa9LnFKpfKjwU6GMUKomyOqARDLWsV8ejOMpZVYuI]othello159@h...[/url
Sent: Tuesday, April 20, 2004 7:20 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Re: unstable temp measurement
Thanks for the help, in particular for Tracy Allens remarks.
I went and got the data sheet to read up on this, it seemed they want the
bypass capacitors at the sensor, not so much at the end of the cable and
closer to the AD chip.
But anyways, I experimented with a few set ups on my bench and also stuck,
as Tracy had suggested, just the LM35 on my scope and indeed, there was some
ripple and hash with surprisingly high frequency, several MHZ.
But I could not get the readings to stabilize until I followed a hunch and
changed power supplies, from a big HP 6433B bench supply to a little shitty
$7 Jameco surplus switching supply and bingo, everything stabilized right
there.
The scope shows isolated 50mV burst among the ripple of the HP, I don't know
what all this means yet but I sure know where these problems suddenly came
from, I apparently introduced them through the supply voltage myself.
I hope this is the end of it...
73 Uwe
--- In basicstamps@yahoogroups.com, Tracy Allen <tracy@e...> wrote:
> The problem is not so much noise, in the sense of external
> influences, it is self-oscillation of the LM34 chip. Micropower
> circuits like the LM34 have a limited capability to drive capacitive
> loads, like a cable. The same thing is true of low-power operational
> amplifiers, like the LM358.
>
> External capacitance gives a phase shift that is just right to make
> the circuit break into a small oscillation. If you hook the output of
> the LM34 directly to an oscilloscope on a ~5mV/div AC range, the
> display will be pretty solide. But if you stick on a cable in the
> neighborhood of 2 feet to 30 feet, you will see an oscillation of as
> much as 30 millivolts, which is equivalent to 3 degrees. Depending on
> your ADC, that will come out as an error of some sort, even when you
> average it.
>
> Micropower op amps also have trouble when a capacitor is suddenly
> attached to their output, as happens when your read the temperature
> with a switched capacitor ADC like the TLC2543. To sample its inputs,
> the ADC suddenly attaches the sampling capacitor to the input to
> collect a sample of the input voltage, and then detaches that
> capacitor to move the sample on into the conversion process. For a
> micropower circuit like the LM34 or an LM358 op amp, that sudden
> change of capacitance is like hitting the output with a sledge hammer,
> and the circuit rings like a bell.
>
> The extra small resistor and capacitor on the output act as "leading"
> compensation. You can look at it this way. The current into the
> capacitor has to flow through the resistor. The voltage across the
> resistor is proportional to the current, and adds to the voltage
> across the capacitor. The current "predicts" or leads the voltage,
> and that is what gets fed back to the input of the op amp inside the
> LM34. In terms of phase, that "leading" compensates for the "lag"
> caused by the open loop resistance of the op-amp. The circuit never
> reaches the point where it goes into oscillation.
>
> The LM34 data sheet explains a lot of this.
>
> -- regards,
> Tracy
>
>
> >In a message dated 4/19/2004 12:11:04 PM Eastern Daylight Time,
> >speakman@o... writes:
> >
> >
> >> Hope you can answer this for me. I am new to Stamps and am having a
> >> similar situation as othello159, except mine was with the LM34 and
> >> unstable measurements. I was hoping you could explain what the
> >> resistor and capacitor are actually doing to make the readings more
> >> accurate.
> >>
> >
> >We use LM34 sensor exclusively in all of our projects. The capacitor
> >gets rid of noise on the ADC input. The resistor and the capacitor
> >also form a rather complicated RC network, which was explained to me
> >but I don't really understand. All I really know is that it works.
> >
> >Sid Weaver
> >Always thinking.....
> >http://www.visualmuses.com/chipcircuit/index.html
> >
> >
To UNSUBSCRIBE, just send mail to:
basicstamps-unsubscribe@yahoogroups.com
from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
Yahoo! Groups Links
The nice ham at the hamfest where I got mine was very happy with $20.
Happy about that purchase, despite the RF noise...
Uwe
--- In basicstamps@yahoogroups.com, "Grover Richardson" <grover.richardson@=
g...> wrote:
> Some of the hp units are switchers, and I checked and found the following=
:::
> http://www.testelectronics.com/used/hp6433b.htm
> Hewlett Packard 6433B
> DC POWER SUPPLY
> The 6433B Power Supply is a SCR based regulated supply which
> provides good high current output capability but also outputs a slight
> amount of ripple. Constant-Voltage/Constant-Current modes. DC output from=
> 0-36V @ 0-10A. Large easy-to-read meters continuously monitor output volt=
age
> and current. Bus bars and terminal blocks on the rear panel provide
> connections for input and output power, remote sensing, remote programmin=
g,
> and auto-series, parallel, and tracking connections. Unit also incorporat=
es
> reverse voltage protection and a fused AC input. Operates from 115 VAC ±1=
0%,
> single phase, 57-63 Hz.
>
> Though it is not a classic switcher (in my mind), it's not a classic line=
ar
> supply. All supplies, not linear, are suspect of serious noise problems.=
>
> Good that you used a scope. I do almost all my troubleshooting on a scop=
e.
> I had an op amp one time that was oscillating at 425 MHz. It was not
> obvious from lower quality instruments what the problem was<G>.
>
> Why the inexpensive switcher was better? I haven't a clue. However, it =
may
> be that you aren't really loading it much, and it only switches on a litt=
le
> every now and then for charging. Load it to about 1/2 of full power and =
see
> if it still puts out a clean signal.
>
> Something else to remember. Switchers that I have used have been serious=
ly
> offended at non-constant loads. We used one on a good sized motorized du=
ne
> buggy when characterizing the motor. We couldn't get the controller
> (digital proportional with digital control) to act right, and the power
> supply kept changing Voltage on us. There was interaction between the
> digital proportion circuits and the switcher.
>
> Good luck.
>
>
>
>
>
>
>
Original Message
> From: othello159 [noparse][[/noparse]mailto[noparse]:o[/noparse]thello159@h...]
> Sent: Tuesday, April 20, 2004 7:20 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Re: unstable temp measurement
>
>
>
> Thanks for the help, in particular for Tracy Allens remarks.
>
> I went and got the data sheet to read up on this, it seemed they want the=
> bypass capacitors at the sensor, not so much at the end of the cable and
> closer to the AD chip.
>
> But anyways, I experimented with a few set ups on my bench and also stuck=
,
> as Tracy had suggested, just the LM35 on my scope and indeed, there was s=
ome
> ripple and hash with surprisingly high frequency, several MHZ.
>
> But I could not get the readings to stabilize until I followed a hunch a=
nd
> changed power supplies, from a big HP 6433B bench supply to a little ****=
ty
> $7 Jameco surplus switching supply and bingo, everything stabilized right=
> there.
>
> The scope shows isolated 50mV burst among the ripple of the HP, I don't k=
now
> what all this means yet but I sure know where these problems suddenly cam=
e
> from, I apparently introduced them through the supply voltage myself.
>
> I hope this is the end of it...
>
> 73 Uwe
>
>
>
>
> --- In basicstamps@yahoogroups.com, Tracy Allen <tracy@e...> wrote:
> > The problem is not so much noise, in the sense of external
> > influences, it is self-oscillation of the LM34 chip. Micropower
> > circuits like the LM34 have a limited capability to drive capacitive
> > loads, like a cable. The same thing is true of low-power operational
> > amplifiers, like the LM358.
> >
> > External capacitance gives a phase shift that is just right to make
> > the circuit break into a small oscillation. If you hook the output of
> > the LM34 directly to an oscilloscope on a ~5mV/div AC range, the
> > display will be pretty solide. But if you stick on a cable in the
> > neighborhood of 2 feet to 30 feet, you will see an oscillation of as
> > much as 30 millivolts, which is equivalent to 3 degrees. Depending on
> > your ADC, that will come out as an error of some sort, even when you
> > average it.
> >
> > Micropower op amps also have trouble when a capacitor is suddenly
> > attached to their output, as happens when your read the temperature
> > with a switched capacitor ADC like the TLC2543. To sample its inputs,
> > the ADC suddenly attaches the sampling capacitor to the input to
> > collect a sample of the input voltage, and then detaches that
> > capacitor to move the sample on into the conversion process. For a
> > micropower circuit like the LM34 or an LM358 op amp, that sudden
> > change of capacitance is like hitting the output with a sledge hammer,
> > and the circuit rings like a bell.
> >
> > The extra small resistor and capacitor on the output act as "leading"
> > compensation. You can look at it this way. The current into the
> > capacitor has to flow through the resistor. The voltage across the
> > resistor is proportional to the current, and adds to the voltage
> > across the capacitor. The current "predicts" or leads the voltage,
> > and that is what gets fed back to the input of the op amp inside the
> > LM34. In terms of phase, that "leading" compensates for the "lag"
> > caused by the open loop resistance of the op-amp. The circuit never
> > reaches the point where it goes into oscillation.
> >
> > The LM34 data sheet explains a lot of this.
> >
> > -- regards,
> > Tracy
> >
> >
> > >In a message dated 4/19/2004 12:11:04 PM Eastern Daylight Time,
> > >speakman@o... writes:
> > >
> > >
> > >> Hope you can answer this for me. I am new to Stamps and am having a
> > >> similar situation as othello159, except mine was with the LM34 and
> > >> unstable measurements. I was hoping you could explain what the
> > >> resistor and capacitor are actually doing to make the readings more
> > >> accurate.
> > >>
> > >
> > >We use LM34 sensor exclusively in all of our projects. The capacitor
> > >gets rid of noise on the ADC input. The resistor and the capacitor
> > >also form a rather complicated RC network, which was explained to me
> > >but I don't really understand. All I really know is that it works.
> > >
> > >Sid Weaver
> > >Always thinking.....
> > >http://www.visualmuses.com/chipcircuit/index.html
> > >
> > >
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and=
> Body of the message will be ignored.
>
> Yahoo! Groups Links
together. By the way, when I get things used, if it comes with a manual or
a schematic, it's worth an extra $20<G>.
If you place a small load on the power supply (say 2 Amps or so), and add
some filtering, you can smooth out the noise usually. It just depends upon
what you call quiet<G>. Since the noise is relatively high in frequency, it
shouldn't take much. Just the standard PI network out of the Amateur Radio
Handbook (one of the older ones<G>) likely would suffice.
Good luck.
Original Message
From: othello159 [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=cM6r9Pp_mcPx9rupQp2K14racfP0ULWBxruGmOucShveMNbY3K1FxdAtw6pGC7PeTmISBXA-R-KN7mc63JauX0Q]othello159@h...[/url
Sent: Wednesday, April 21, 2004 11:45 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Re: unstable temp measurement
Oh my, the site you referred to, they want $800 for that HP power supply!!
The nice ham at the hamfest where I got mine was very happy with $20.
Happy about that purchase, despite the RF noise...
Uwe
--- In basicstamps@yahoogroups.com, "Grover Richardson" <grover.richardson@=
g...> wrote:
> Some of the hp units are switchers, and I checked and found the
> following=
:::
> http://www.testelectronics.com/used/hp6433b.htm
> Hewlett Packard 6433B
> DC POWER SUPPLY
> The 6433B Power Supply is a SCR based regulated supply which
provides
> good high current output capability but also outputs a slight amount
> of ripple. Constant-Voltage/Constant-Current modes. DC output from=
> 0-36V @ 0-10A. Large easy-to-read meters continuously monitor output
> volt=
age
> and current. Bus bars and terminal blocks on the rear panel provide
> connections for input and output power, remote sensing, remote
> programmin=
g,
> and auto-series, parallel, and tracking connections. Unit also
> incorporat=
es
> reverse voltage protection and a fused AC input. Operates from 115 VAC
> ±1=
0%,
> single phase, 57-63 Hz.
>
> Though it is not a classic switcher (in my mind), it's not a classic
> line=
ar
> supply. All supplies, not linear, are suspect of serious noise
> problems.=
>
> Good that you used a scope. I do almost all my troubleshooting on a
> scop=
e.
> I had an op amp one time that was oscillating at 425 MHz. It was not
> obvious from lower quality instruments what the problem was<G>.
>
> Why the inexpensive switcher was better? I haven't a clue. However,
> it =
may
> be that you aren't really loading it much, and it only switches on a
> litt=
le
> every now and then for charging. Load it to about 1/2 of full power
> and =
see
> if it still puts out a clean signal.
>
> Something else to remember. Switchers that I have used have been
> serious=
ly
> offended at non-constant loads. We used one on a good sized motorized
> du=
ne
> buggy when characterizing the motor. We couldn't get the controller
> (digital proportional with digital control) to act right, and the
> power supply kept changing Voltage on us. There was interaction
> between the digital proportion circuits and the switcher.
>
> Good luck.
>
>
>
>
>
>
>
Original Message
> From: othello159 [noparse][[/noparse]mailto[noparse]:o[/noparse]thello159@h...]
> Sent: Tuesday, April 20, 2004 7:20 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Re: unstable temp measurement
>
>
>
> Thanks for the help, in particular for Tracy Allens remarks.
>
> I went and got the data sheet to read up on this, it seemed they want
> the=
> bypass capacitors at the sensor, not so much at the end of the cable
> and closer to the AD chip.
>
> But anyways, I experimented with a few set ups on my bench and also
> stuck=
,
> as Tracy had suggested, just the LM35 on my scope and indeed, there
> was s=
ome
> ripple and hash with surprisingly high frequency, several MHZ.
>
> But I could not get the readings to stabilize until I followed a
> hunch a=
nd
> changed power supplies, from a big HP 6433B bench supply to a little
> ****=
ty
> $7 Jameco surplus switching supply and bingo, everything stabilized
> right=
> there.
>
> The scope shows isolated 50mV burst among the ripple of the HP, I
> don't k=
now
> what all this means yet but I sure know where these problems suddenly
> cam=
e
> from, I apparently introduced them through the supply voltage myself.
>
> I hope this is the end of it...
>
> 73 Uwe
>
>
>
>
> --- In basicstamps@yahoogroups.com, Tracy Allen <tracy@e...> wrote:
> > The problem is not so much noise, in the sense of external
> > influences, it is self-oscillation of the LM34 chip. Micropower
> > circuits like the LM34 have a limited capability to drive capacitive
> > loads, like a cable. The same thing is true of low-power operational
> > amplifiers, like the LM358.
> >
> > External capacitance gives a phase shift that is just right to make
> > the circuit break into a small oscillation. If you hook the output
> > of the LM34 directly to an oscilloscope on a ~5mV/div AC range, the
> > display will be pretty solide. But if you stick on a cable in the
> > neighborhood of 2 feet to 30 feet, you will see an oscillation of as
> > much as 30 millivolts, which is equivalent to 3 degrees. Depending
> > on your ADC, that will come out as an error of some sort, even when
> > you average it.
> >
> > Micropower op amps also have trouble when a capacitor is suddenly
> > attached to their output, as happens when your read the temperature
> > with a switched capacitor ADC like the TLC2543. To sample its
> > inputs, the ADC suddenly attaches the sampling capacitor to the
> > input to collect a sample of the input voltage, and then detaches
> > that capacitor to move the sample on into the conversion process.
> > For a micropower circuit like the LM34 or an LM358 op amp, that
> > sudden change of capacitance is like hitting the output with a
> > sledge hammer, and the circuit rings like a bell.
> >
> > The extra small resistor and capacitor on the output act as
> > "leading" compensation. You can look at it this way. The current
> > into the capacitor has to flow through the resistor. The voltage
> > across the resistor is proportional to the current, and adds to the
> > voltage across the capacitor. The current "predicts" or leads the
> > voltage, and that is what gets fed back to the input of the op amp
> > inside the LM34. In terms of phase, that "leading" compensates for
> > the "lag" caused by the open loop resistance of the op-amp. The
> > circuit never reaches the point where it goes into oscillation.
> >
> > The LM34 data sheet explains a lot of this.
> >
> > -- regards,
> > Tracy
> >
> >
> > >In a message dated 4/19/2004 12:11:04 PM Eastern Daylight Time,
> > >speakman@o... writes:
> > >
> > >
> > >> Hope you can answer this for me. I am new to Stamps and am having
> > >> a similar situation as othello159, except mine was with the LM34
> > >> and unstable measurements. I was hoping you could explain what
> > >> the resistor and capacitor are actually doing to make the
> > >> readings more accurate.
> > >>
> > >
> > >We use LM34 sensor exclusively in all of our projects. The
> > >capacitor gets rid of noise on the ADC input. The resistor and the
> > >capacitor also form a rather complicated RC network, which was
> > >explained to me but I don't really understand. All I really know
> > >is that it works.
> > >
> > >Sid Weaver
> > >Always thinking.....
> > >http://www.visualmuses.com/chipcircuit/index.html
> > >
> > >
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
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> and=
> Body of the message will be ignored.
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Yahoo! Groups Links
voltages, currents and frequencies for calibration purposes.
However, it has a switching power supply inside that feeds through
noise onto the signal at the millivolt level. It was some time and
head scratching before I discovered where the unstable measurements
were coming from, because you always expect instruments you buy to do
exactly what they say, with no gotchas. Right!? After I tracked
down the problem, I was able to work around it at low milivolt and
microvolt levels with an external precision voltage divider, filter,
and buffer. Despite that, he instrument is still one of our most
useful tools, to be able to dial in any setting and step through
settings to test for linearity of amplifiers, etc. I don't know if
the Fluke process calibrator would have the same issues, but I do
know the Fluke is a lot more expensive!
-- Tracy
>Oh my, the site you referred to, they want $800 for that HP power supply!!
>The nice ham at the hamfest where I got mine was very happy with $20.
>
>Happy about that purchase, despite the RF noise...
>
>Uwe
>
>
>--- In basicstamps@yahoogroups.com, "Grover Richardson" <grover.richardson@=
>g...> wrote:
>> Some of the hp units are switchers, and I checked and found the following=
>:::
>> http://www.testelectronics.com/used/hp6433b.htm
>> Hewlett Packard 6433B
>> DC POWER SUPPLY
>> The 6433B Power Supply is a SCR based regulated supply which
>> provides good high current output capability but also outputs a slight
>> amount of ripple. Constant-Voltage/Constant-Current modes. DC output from=
>
>> 0-36V @ 0-10A. Large easy-to-read meters continuously monitor output volt=
>age
>> and current. Bus bars and terminal blocks on the rear panel provide
>> connections for input and output power, remote sensing, remote programmin=
>g,
>> and auto-series, parallel, and tracking connections. Unit also incorporat=
>es
>> reverse voltage protection and a fused AC input. Operates from 115 VAC ±1=
>0%,
>> single phase, 57-63 Hz.
>>
>> Though it is not a classic switcher (in my mind), it's not a classic line=
>ar
>> supply. All supplies, not linear, are suspect of serious noise problems.=
>
>>
>> Good that you used a scope. I do almost all my troubleshooting on a scop=
>e.
>> I had an op amp one time that was oscillating at 425 MHz. It was not
>> obvious from lower quality instruments what the problem was<G>.
>>
>> Why the inexpensive switcher was better? I haven't a clue. However, it =
>may
>> be that you aren't really loading it much, and it only switches on a litt=
>le
>> every now and then for charging. Load it to about 1/2 of full power and =
>see
>> if it still puts out a clean signal.
>>
>> Something else to remember. Switchers that I have used have been serious=
>ly
>> offended at non-constant loads. We used one on a good sized motorized du=
>ne
>> buggy when characterizing the motor. We couldn't get the controller
>> (digital proportional with digital control) to act right, and the power
>> supply kept changing Voltage on us. There was interaction between the
>> digital proportion circuits and the switcher.
>>
>> Good luck.
>>
>>
>>
>>
>>
>>
>>
Original Message
>> From: othello159 [noparse][[/noparse]mailto[noparse]:o[/noparse]thello159@h...]
>> Sent: Tuesday, April 20, 2004 7:20 PM
>> To: basicstamps@yahoogroups.com
>> Subject: [noparse][[/noparse]basicstamps] Re: unstable temp measurement
>>
>>
>>
>> Thanks for the help, in particular for Tracy Allens remarks.
>>
>> I went and got the data sheet to read up on this, it seemed they want the=
>
>> bypass capacitors at the sensor, not so much at the end of the cable and
>> closer to the AD chip.
>>
>> But anyways, I experimented with a few set ups on my bench and also stuck=
>,
>> as Tracy had suggested, just the LM35 on my scope and indeed, there was s=
>ome
>> ripple and hash with surprisingly high frequency, several MHZ.
>>
>> But I could not get the readings to stabilize until I followed a hunch a=
>nd
>> changed power supplies, from a big HP 6433B bench supply to a little ****=
>ty
>> $7 Jameco surplus switching supply and bingo, everything stabilized right=
>
>> there.
>>
>> The scope shows isolated 50mV burst among the ripple of the HP, I don't k=
>now
>> what all this means yet but I sure know where these problems suddenly cam=
>e
>> from, I apparently introduced them through the supply voltage myself.
>>
>> I hope this is the end of it...
>>
>> 73 Uwe
>>
>>
>>
>>
>> --- In basicstamps@yahoogroups.com, Tracy Allen <tracy@e...> wrote:
>> > The problem is not so much noise, in the sense of external
>> > influences, it is self-oscillation of the LM34 chip. Micropower
>> > circuits like the LM34 have a limited capability to drive capacitive
>> > loads, like a cable. The same thing is true of low-power operational
>> > amplifiers, like the LM358.
>> >
>> > External capacitance gives a phase shift that is just right to make
>> > the circuit break into a small oscillation. If you hook the output of
>> > the LM34 directly to an oscilloscope on a ~5mV/div AC range, the
>> > display will be pretty solide. But if you stick on a cable in the
>> > neighborhood of 2 feet to 30 feet, you will see an oscillation of as
>> > much as 30 millivolts, which is equivalent to 3 degrees. Depending on
>> > your ADC, that will come out as an error of some sort, even when you
>> > average it.
>> >
>> > Micropower op amps also have trouble when a capacitor is suddenly
>> > attached to their output, as happens when your read the temperature
>> > with a switched capacitor ADC like the TLC2543. To sample its inputs,
>> > the ADC suddenly attaches the sampling capacitor to the input to
>> > collect a sample of the input voltage, and then detaches that
>> > capacitor to move the sample on into the conversion process. For a
>> > micropower circuit like the LM34 or an LM358 op amp, that sudden
>> > change of capacitance is like hitting the output with a sledge hammer,
>> > and the circuit rings like a bell.
>> >
>> > The extra small resistor and capacitor on the output act as "leading"
>> > compensation. You can look at it this way. The current into the
>> > capacitor has to flow through the resistor. The voltage across the
>> > resistor is proportional to the current, and adds to the voltage
>> > across the capacitor. The current "predicts" or leads the voltage,
>> > and that is what gets fed back to the input of the op amp inside the
>> > LM34. In terms of phase, that "leading" compensates for the "lag"
>> > caused by the open loop resistance of the op-amp. The circuit never
>> > reaches the point where it goes into oscillation.
>> >
>> > The LM34 data sheet explains a lot of this.
>> >
>> > -- regards,
>> > Tracy
>> >
>> >
>> > >In a message dated 4/19/2004 12:11:04 PM Eastern Daylight Time,
>> > >speakman@o... writes:
>> > >
>> > >
>> > >> Hope you can answer this for me. I am new to Stamps and am having a
>> > >> similar situation as othello159, except mine was with the LM34 and
>> > >> unstable measurements. I was hoping you could explain what the
>> > >> resistor and capacitor are actually doing to make the readings more
>> > >> accurate.
>> > >>
>> > >
>> > >We use LM34 sensor exclusively in all of our projects. The capacitor
>> > >gets rid of noise on the ADC input. The resistor and the capacitor
>> > >also form a rather complicated RC network, which was explained to me
>> > >but I don't really understand. All I really know is that it works.
>> > >
>> > >Sid Weaver
>> > >Always thinking.....
>> > >http://www.visualmuses.com/chipcircuit/index.html
>> > >
>
> > > >
Back when the unstable temp measurements first occured changing the power supply solved the problem.
Now the little circuit (basic stamp 2 with an 0831 A/D converter and a LM35 temp sensor, the stamp compares temps from two sensors and switches a relais through a Darlington IC) is ready to go into its final box (it controls the circulator pump for my hot water solar system) and suddenly, as I connect the circuit to a car battery, its permanent power source, I have these oscillations again.
The countermeasures (see Allens note below) were still in place on one LM35 ( I am using two) but it didn't make any difference, both sensors were all over the place.
So I connected a small cap across the battery terminal and everything went quite and back to normal.
So I proceed and connect the relais for the pump and the whole circuit went wild again. Disconnect the relais and the sensors readings go back to normal.
Two things.
First I need to get the circuit to behave WITH the relay.
Second I am wondering if there are broader general design guidelines to plan countermeasures against these gremlines into the circuit right from the start (as opposed to what I do right now which is deal with it when it happens). At this point I am afraid to move the circuit to another room, who knows what will happen then...
Your advice will be appreciated
Uwe
--- In basicstamps@yahoogroups.com, Tracy Allen <tracy@e...> wrote:
> The problem is not so much noise, in the sense of external
> influences, it is self-oscillation of the LM34 chip. Micropower
> circuits like the LM34 have a limited capability to drive capacitive
> loads, like a cable. The same thing is true of low-power operational
> amplifiers, like the LM358.
>
> External capacitance gives a phase shift that is just right to make
> the circuit break into a small oscillation. If you hook the output
> of the LM34 directly to an oscilloscope on a ~5mV/div AC range, the
> display will be pretty solide. But if you stick on a cable in the
> neighborhood of 2 feet to 30 feet, you will see an oscillation of as
> much as 30 millivolts, which is equivalent to 3 degrees. Depending
> on your ADC, that will come out as an error of some sort, even when
> you average it.
>
> Micropower op amps also have trouble when a capacitor is suddenly
> attached to their output, as happens when your read the temperature
> with a switched capacitor ADC like the TLC2543. To sample its
> inputs, the ADC suddenly attaches the sampling capacitor to the input
> to collect a sample of the input voltage, and then detaches that
> capacitor to move the sample on into the conversion process. For a
> micropower circuit like the LM34 or an LM358 op amp, that sudden
> change of capacitance is like hitting the output with a sledge
> hammer, and the circuit rings like a bell.
>
> The extra small resistor and capacitor on the output act as "leading"
> compensation. You can look at it this way. The current into the
> capacitor has to flow through the resistor. The voltage across the
> resistor is proportional to the current, and adds to the voltage
> across the capacitor. The current "predicts" or leads the voltage,
> and that is what gets fed back to the input of the op amp inside the
> LM34. In terms of phase, that "leading" compensates for the "lag"
> caused by the open loop resistance of the op-amp. The circuit never
> reaches the point where it goes into oscillation.
>
> The LM34 data sheet explains a lot of this.
>
> -- regards,
> Tracy
>
>
> >In a message dated 4/19/2004 12:11:04 PM Eastern Daylight Time,
> >speakman@o... writes:
> >
> >
> >> Hope you can answer this for me. I am new to Stamps and am having a
> >> similar situation as othello159, except mine was with the LM34 and
> >> unstable measurements. I was hoping you could explain what the
> >> resistor and capacitor are actually doing to make the readings more
> >> accurate.
> >>
> >
> >We use LM34 sensor exclusively in all of our projects. The capacitor gets
> >rid of noise on the ADC input. The resistor and the capacitor also form a
> >rather complicated RC network, which was explained to me but I don't really
> >understand. All I really know is that it works.
> >
> >Sid Weaver
> >Always thinking.....
> >http://www.visualmuses.com/chipcircuit/index.html
> >
> >
the current setup is connected to a battery? Is the battery being charged
as you use it?
What's your environment like? Fluorescent lights abound? Motors running in
the back ground?
How are you prototyping this? on a breadboard or perfboard? Most
breadboards have a metal bottom plate for shielding.
make sur eyou have the 'kick-back' diode in parallel to the relay coil since
this will throw back voltage to your stamp when it's fields collapse.
Long leads on your components?
What happens when you pull the LM35? Does your A/D float enough that you
get random numbers?
How are you powering the relay?!
Wow, I'm full of questions today....haha
sb
Original Message
From: "othello159" <othello159@h...>
To: <basicstamps@yahoogroups.com>
Sent: Wednesday, May 19, 2004 11:51 PM
Subject: [noparse][[/noparse]basicstamps] Re: unstable temp measurement
> I have to revive this thread....
>
> Back when the unstable temp measurements first occured changing the power
supply solved the problem.
>
> Now the little circuit (basic stamp 2 with an 0831 A/D converter and a
LM35 temp sensor, the stamp compares temps from two sensors and switches a
relais through a Darlington IC) is ready to go into its final box (it
controls the circulator pump for my hot water solar system) and suddenly, as
I connect the circuit to a car battery, its permanent power source, I have
these oscillations again.
>
> The countermeasures (see Allens note below) were still in place on one
LM35 ( I am using two) but it didn't make any difference, both sensors were
all over the place.
> So I connected a small cap across the battery terminal and everything went
quite and back to normal.
>
> So I proceed and connect the relais for the pump and the whole circuit
went wild again. Disconnect the relais and the sensors readings go back to
normal.
>
>
> Two things.
>
> First I need to get the circuit to behave WITH the relay.
>
> Second I am wondering if there are broader general design guidelines to
plan countermeasures against these gremlines into the circuit right from the
start (as opposed to what I do right now which is deal with it when it
happens). At this point I am afraid to move the circuit to another room,
who knows what will happen then...
>
>
> Your advice will be appreciated
>
> Uwe
>
>
>
>
> --- In basicstamps@yahoogroups.com, Tracy Allen <tracy@e...> wrote:
> > The problem is not so much noise, in the sense of external
> > influences, it is self-oscillation of the LM34 chip. Micropower
> > circuits like the LM34 have a limited capability to drive capacitive
> > loads, like a cable. The same thing is true of low-power operational
> > amplifiers, like the LM358.
> >
> > External capacitance gives a phase shift that is just right to make
> > the circuit break into a small oscillation. If you hook the output
> > of the LM34 directly to an oscilloscope on a ~5mV/div AC range, the
> > display will be pretty solide. But if you stick on a cable in the
> > neighborhood of 2 feet to 30 feet, you will see an oscillation of as
> > much as 30 millivolts, which is equivalent to 3 degrees. Depending
> > on your ADC, that will come out as an error of some sort, even when
> > you average it.
> >
> > Micropower op amps also have trouble when a capacitor is suddenly
> > attached to their output, as happens when your read the temperature
> > with a switched capacitor ADC like the TLC2543. To sample its
> > inputs, the ADC suddenly attaches the sampling capacitor to the input
> > to collect a sample of the input voltage, and then detaches that
> > capacitor to move the sample on into the conversion process. For a
> > micropower circuit like the LM34 or an LM358 op amp, that sudden
> > change of capacitance is like hitting the output with a sledge
> > hammer, and the circuit rings like a bell.
> >
> > The extra small resistor and capacitor on the output act as "leading"
> > compensation. You can look at it this way. The current into the
> > capacitor has to flow through the resistor. The voltage across the
> > resistor is proportional to the current, and adds to the voltage
> > across the capacitor. The current "predicts" or leads the voltage,
> > and that is what gets fed back to the input of the op amp inside the
> > LM34. In terms of phase, that "leading" compensates for the "lag"
> > caused by the open loop resistance of the op-amp. The circuit never
> > reaches the point where it goes into oscillation.
> >
> > The LM34 data sheet explains a lot of this.
> >
> > -- regards,
> > Tracy
> >
> >
> > >In a message dated 4/19/2004 12:11:04 PM Eastern Daylight Time,
> > >speakman@o... writes:
> > >
> > >
> > >> Hope you can answer this for me. I am new to Stamps and am having a
> > >> similar situation as othello159, except mine was with the LM34 and
> > >> unstable measurements. I was hoping you could explain what the
> > >> resistor and capacitor are actually doing to make the readings more
> > >> accurate.
> > >>
> > >
> > >We use LM34 sensor exclusively in all of our projects. The capacitor
gets
> > >rid of noise on the ADC input. The resistor and the capacitor also
form a
> > >rather complicated RC network, which was explained to me but I don't
really
> > >understand. All I really know is that it works.
> > >
> > >Sid Weaver
> > >Always thinking.....
> > >http://www.visualmuses.com/chipcircuit/index.html
> > >
> > >
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
> Yahoo! Groups Links
>
>
>
>
>
wrote:
> I have to revive this thread....
>
> Back when the unstable temp measurements first occurred changing
the power supply solved the problem.
>
> Now the little circuit (basic stamp 2 with an 0831 A/D converter
and a LM35 temp sensor, the stamp compares temps from two sensors and
switches a relays through a Darlington IC) is ready to go into its
final box (it controls the circulator pump for my hot water solar
system) and suddenly, as I connect the circuit to a car battery, its
permanent power source, I have these oscillations again.
.
.
.
This brings up a few questions. What else is on the power line ?
how long are the leads ? does it only happen when you are using your
cell phone, or the neighbor is on his HAM radio ? Are there electric
motors in the area....
Getting a good isolation from any and everything on the power supply
is not terribly difficult, and may need a DC to DC converter to
really isolate you. Since you only have DC, you lose the simplicity
of a transformer. Also if you have a battery charger with some pulse
circuit, you may be creating the problems.
Let us know more about your battery and charger. A power supply re-
design may be in order.
Or, control of the pulse generator (desulphator?) where it runs 90%
of the time, you shut it off, take a temp reading, then turn it back
on ??
(btw, I think I get brownie points if I gueseed this !)
> The countermeasures (see Allens note below) were still in place on
one LM35 ( I am using two) but it didn't make any difference, both
sensors were all over the place.
> So I connected a small cap across the battery terminal and
everything went quite and back to normal.
>
> So I proceed and connect the relays for the pump and the whole
circuit went wild again. Disconnect the relays and the sensors
readings go back to normal.
>
.
.
.
relays can be a PITA. there are many different types and voltages
for them.
As you mentioned pumps, those motors may be part of the problem.
Consider this test. Since a relay on the logic side of your power
line filters will cause problems, it would be best if you kept your
logic separate from the power side.
I'm assuming your pump relays are connected to the power side of any
line filters (caps or whatever for your logic)
Also, since a relay switching will cause a spike, don't try to read
data for 20 seconds after you change state. that would eliminate any
spike from being part of your data.
When designing a board with known PWM or other switching, we often
add a cap to the power supply of the micro to filter the spikes in
the power line. This would be right at the connection of the Stamp
or very close to it.
Another question is what pins you are using to power the Stamp ? And
what is connected to the voltage regulator of the Stamp ? are you
powering other things with the on-board VR of the Stamp ?
Second, run a completely separate power line from your battery to
your board and then have only your output signal and ground to the
transistor that drives your relay. In other words, get your relay
board including mosfet or transistor out of the logic and over into
the power side.
That way, only your logic signals are in your box.
And possibly use an opto-isolator to control the relays. That way,
all your power is on one filtered line.
Use shielded cable to your temperature sensor and don't connect
ground to both side, but keep the field sensor insulated from the
rest of the system by glass or plastic or something. that way, no
wire of your logic touches anything outside of the parts shown on
your schematic.
This would mean to NOT let the sensor wire or shield or ground touch
any pipes or containers or anything.
> Second I am wondering if there are broader general design
guidelines to plan countermeasures against these gremlins into the
circuit right from the start (as opposed to what I do right now which
is deal with it when it happens). At this point I am afraid to move
the circuit to another room, who knows what will happen then...
.
.
.
Generally, there are two ways I look at things. Over design or under
design.
If you over design, you use opto's all over the place and have a
completely isolated power source, all in a hermetically sealed
container that is rf shielded and temperature controlled.
If you under design, you only need the very few parts that should
work and fix as you go.
Most of us start with under design and then work up. It makes the
most cost and time effective way.
check out an op-amp amplifier circuit and then a op-amp instrument
schematic. basically the same thing in principal. vastly different
parts counts. The instrument connection uses both the 'in' and non-
in connections so as to allow a termperature shift to cancel each
other out (amung other things)
Dave
The intent is to run the controller off a battery which is connected to a float charger, the charger was unplugged when I tested the basic stamp circuit, since the charger transmitts on 20 m...
I had hoped to be past prototyping and the whole circuit is on a printed circuit board I made, with molex connectors so all peripherals come off quite easily.
And yes there is a diode and a small cap on the relay.
The relay is switched through a Darlington array (ULN 2803) which is activated through the stamp.
All componnts are on the PC board, so lead length should not be an issue and the temporarily connected LM35's are on 6" wire, so is the relay.
Steve, following your question I disconnected one of my two LM35's and indeed I continue to get jumpy and false temp readings.
Currently everything works just fine until I plug in the relay at which point the circuit goes wild, even when the relay doesn't switch. So just the coil being connected to the ULN2803 downstream from the stamp must do something to the circuit. I would have said it probably receives signals from my answering machine but that was off-[noparse]:)[/noparse]
regards Uwe
--- In basicstamps@yahoogroups.com, "SB" <steve.brady@r...> wrote:
> I never did see this thread....but you mention a power issue....
> the current setup is connected to a battery? Is the battery being charged
> as you use it?
>
> What's your environment like? Fluorescent lights abound? Motors running in
> the back ground?
>
> How are you prototyping this? on a breadboard or perfboard? Most
> breadboards have a metal bottom plate for shielding.
>
> make sur eyou have the 'kick-back' diode in parallel to the relay coil since
> this will throw back voltage to your stamp when it's fields collapse.
> Long leads on your components?
>
> What happens when you pull the LM35? Does your A/D float enough that you
> get random numbers?
> How are you powering the relay?!
>
> Wow, I'm full of questions today....haha
> sb
>
>
Original Message
> From: "othello159" <othello159@h...>
> To: <basicstamps@yahoogroups.com>
> Sent: Wednesday, May 19, 2004 11:51 PM
> Subject: [noparse][[/noparse]basicstamps] Re: unstable temp measurement
>
>
> > I have to revive this thread....
> >
> > Back when the unstable temp measurements first occured changing the power
> supply solved the problem.
> >
> > Now the little circuit (basic stamp 2 with an 0831 A/D converter and a
> LM35 temp sensor, the stamp compares temps from two sensors and switches a
> relais through a Darlington IC) is ready to go into its final box (it
> controls the circulator pump for my hot water solar system) and suddenly, as
> I connect the circuit to a car battery, its permanent power source, I have
> these oscillations again.
> >
> > The countermeasures (see Allens note below) were still in place on one
> LM35 ( I am using two) but it didn't make any difference, both sensors were
> all over the place.
> > So I connected a small cap across the battery terminal and everything went
> quite and back to normal.
> >
> > So I proceed and connect the relais for the pump and the whole circuit
> went wild again. Disconnect the relais and the sensors readings go back to
> normal.
> >
> >
> > Two things.
> >
> > First I need to get the circuit to behave WITH the relay.
> >
> > Second I am wondering if there are broader general design guidelines to
> plan countermeasures against these gremlines into the circuit right from the
> start (as opposed to what I do right now which is deal with it when it
> happens). At this point I am afraid to move the circuit to another room,
> who knows what will happen then...
> >
> >
> > Your advice will be appreciated
> >
> > Uwe
> >
> >
> >
> >
> > --- In basicstamps@yahoogroups.com, Tracy Allen <tracy@e...> wrote:
> > > The problem is not so much noise, in the sense of external
> > > influences, it is self-oscillation of the LM34 chip. Micropower
> > > circuits like the LM34 have a limited capability to drive capacitive
> > > loads, like a cable. The same thing is true of low-power operational
> > > amplifiers, like the LM358.
> > >
> > > External capacitance gives a phase shift that is just right to make
> > > the circuit break into a small oscillation. If you hook the output
> > > of the LM34 directly to an oscilloscope on a ~5mV/div AC range, the
> > > display will be pretty solide. But if you stick on a cable in the
> > > neighborhood of 2 feet to 30 feet, you will see an oscillation of as
> > > much as 30 millivolts, which is equivalent to 3 degrees. Depending
> > > on your ADC, that will come out as an error of some sort, even when
> > > you average it.
> > >
> > > Micropower op amps also have trouble when a capacitor is suddenly
> > > attached to their output, as happens when your read the temperature
> > > with a switched capacitor ADC like the TLC2543. To sample its
> > > inputs, the ADC suddenly attaches the sampling capacitor to the input
> > > to collect a sample of the input voltage, and then detaches that
> > > capacitor to move the sample on into the conversion process. For a
> > > micropower circuit like the LM34 or an LM358 op amp, that sudden
> > > change of capacitance is like hitting the output with a sledge
> > > hammer, and the circuit rings like a bell.
> > >
> > > The extra small resistor and capacitor on the output act as "leading"
> > > compensation. You can look at it this way. The current into the
> > > capacitor has to flow through the resistor. The voltage across the
> > > resistor is proportional to the current, and adds to the voltage
> > > across the capacitor. The current "predicts" or leads the voltage,
> > > and that is what gets fed back to the input of the op amp inside the
> > > LM34. In terms of phase, that "leading" compensates for the "lag"
> > > caused by the open loop resistance of the op-amp. The circuit never
> > > reaches the point where it goes into oscillation.
> > >
> > > The LM34 data sheet explains a lot of this.
> > >
> > > -- regards,
> > > Tracy
> > >
> > >
> > > >In a message dated 4/19/2004 12:11:04 PM Eastern Daylight Time,
> > > >speakman@o... writes:
> > > >
> > > >
> > > >> Hope you can answer this for me. I am new to Stamps and am having a
> > > >> similar situation as othello159, except mine was with the LM34 and
> > > >> unstable measurements. I was hoping you could explain what the
> > > >> resistor and capacitor are actually doing to make the readings more
> > > >> accurate.
> > > >>
> > > >
> > > >We use LM34 sensor exclusively in all of our projects. The capacitor
> gets
> > > >rid of noise on the ADC input. The resistor and the capacitor also
> form a
> > > >rather complicated RC network, which was explained to me but I don't
> really
> > > >understand. All I really know is that it works.
> > > >
> > > >Sid Weaver
> > > >Always thinking.....
> > > >http://www.visualmuses.com/chipcircuit/index.html
> > > >
> > > >
> >
> >
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> > from the same email address that you subscribed. Text in the Subject and
> Body of the message will be ignored.
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
steve.brady@r... writes:
> I can't remember which is which...but you have one power pin on the stamp
> that you provide exactly +5V and it runs there. Then there's another pin
> that takes something a bit less regulated (can someone confirm that?)
> Anyhow, if you have a power supply, maybe provide power with that instead of
> the regulator.
> Also, I'm guessing you have a couple caps for setting up your
> regulator....check these and make sure your solder joints are good.
>
I just got into this discussion - are you talking about VRef+ on your ADC
chip?
Sid
[noparse][[/noparse]Non-text portions of this message have been removed]
> --- In basicstamps@yahoogroups.com, "othello159" <othello159@h...>
> wrote:
>
>
> > I have to revive this thread....
> >
> > Back when the unstable temp measurements first occurred changing
> the power supply solved the problem.
> >
> > Now the little circuit (basic stamp 2 with an 0831 A/D converter
> and a LM35 temp sensor, the stamp compares temps from two sensors and
> switches a relays through a Darlington IC) is ready to go into its
> final box (it controls the circulator pump for my hot water solar
> system) and suddenly, as I connect the circuit to a car battery, its
> permanent power source, I have these oscillations again.
> .
> .
> .
> This brings up a few questions. What else is on the power line ?
> how long are the leads ? does it only happen when you are using your
> cell phone, or the neighbor is on his HAM radio ? Are there electric
> motors in the area....
>
> Getting a good isolation from any and everything on the power supply
> is not terribly difficult, and may need a DC to DC converter to
> really isolate you. Since you only have DC, you lose the simplicity
> of a transformer. Also if you have a battery charger with some pulse
> circuit, you may be creating the problems.
>
> Let us know more about your battery and charger. A power supply re-
> design may be in order.
>
> Or, control of the pulse generator (desulphator?) where it runs 90%
> of the time, you shut it off, take a temp reading, then turn it back
> on ??
>
> (btw, I think I get brownie points if I gueseed this !)
>
>
> > The countermeasures (see Allens note below) were still in place on
> one LM35 ( I am using two) but it didn't make any difference, both
> sensors were all over the place.
> > So I connected a small cap across the battery terminal and
> everything went quite and back to normal.
> >
> > So I proceed and connect the relays for the pump and the whole
> circuit went wild again. Disconnect the relays and the sensors
> readings go back to normal.
> >
> .
> .
> .
> relays can be a PITA. there are many different types and voltages
> for them.
>
>
> As you mentioned pumps, those motors may be part of the problem.
>
> Consider this test. Since a relay on the logic side of your power
> line filters will cause problems, it would be best if you kept your
> logic separate from the power side.
>
> I'm assuming your pump relays are connected to the power side of any
> line filters (caps or whatever for your logic)
>
> Also, since a relay switching will cause a spike, don't try to read
> data for 20 seconds after you change state. that would eliminate any
> spike from being part of your data.
>
> When designing a board with known PWM or other switching, we often
> add a cap to the power supply of the micro to filter the spikes in
> the power line. This would be right at the connection of the Stamp
> or very close to it.
>
> Another question is what pins you are using to power the Stamp ? And
> what is connected to the voltage regulator of the Stamp ? are you
> powering other things with the on-board VR of the Stamp ?
>
>
> Second, run a completely separate power line from your battery to
> your board and then have only your output signal and ground to the
> transistor that drives your relay. In other words, get your relay
> board including mosfet or transistor out of the logic and over into
> the power side.
>
> That way, only your logic signals are in your box.
>
> And possibly use an opto-isolator to control the relays. That way,
> all your power is on one filtered line.
>
> Use shielded cable to your temperature sensor and don't connect
> ground to both side, but keep the field sensor insulated from the
> rest of the system by glass or plastic or something. that way, no
> wire of your logic touches anything outside of the parts shown on
> your schematic.
>
> This would mean to NOT let the sensor wire or shield or ground touch
> any pipes or containers or anything.
>
>
>
>
> > Second I am wondering if there are broader general design
> guidelines to plan countermeasures against these gremlins into the
> circuit right from the start (as opposed to what I do right now which
> is deal with it when it happens). At this point I am afraid to move
> the circuit to another room, who knows what will happen then...
> .
> .
> .
> Generally, there are two ways I look at things. Over design or under
> design.
>
> If you over design, you use opto's all over the place and have a
> completely isolated power source, all in a hermetically sealed
> container that is rf shielded and temperature controlled.
>
> If you under design, you only need the very few parts that should
> work and fix as you go.
>
> Most of us start with under design and then work up. It makes the
> most cost and time effective way.
>
>
> check out an op-amp amplifier circuit and then a op-amp instrument
> schematic. basically the same thing in principal. vastly different
> parts counts. The instrument connection uses both the 'in' and non-
> in connections so as to allow a termperature shift to cancel each
> other out (amung other things)
>
>
> Dave
Dave, I just answered Steve's questions but you raise a few more so here we go.
The test I mentioned was done with just a battery and my circuit, no 110V power etc, no filters nothing.
I use the Vin pin on the stamp to connect to my 12V car battery. I use a 78L05 to reduce that voltage for my A/D converters, nothing is connected to the regulator of the stamp.
And just as I am writing this to you, olala, I realize that my 78L05 VR supplies the A/D converter as well as the relay with 5V and the switching is done through the darlington which pulls the neg. side of the relay to ground.
Yeez, could that be a conflict area???
Dave I will digest your other questions and respond soon.
thanks for the help
Uwe
I can't remember which is which...but you have one power pin on the stamp
that you provide exactly +5V and it runs there. Then there's another pin
that takes something a bit less regulated (can someone confirm that?)
Anyhow, if you have a power supply, maybe provide power with that instead of
the regulator.
Also, I'm guessing you have a couple caps for setting up your
regulator....check these and make sure your solder joints are good.
As far as the relay....you did say you had the problem before connecting the
relay so the coil kicking dirt on to your ground plane isn't as much an
issue. Might've missed that..I'm not sure.
without the relay...were you still using the darlington?
Is the stamp powered for any length of time before this happens? (thermal
issues?)
Original Message
From: "othello159" <othello159@h...>
To: <basicstamps@yahoogroups.com>
Sent: Thursday, May 20, 2004 2:11 PM
Subject: [noparse][[/noparse]basicstamps] Re: unstable temp measurement
> --- In basicstamps@yahoogroups.com, "Dave Mucha" <davemucha@j...> wrote:
> > --- In basicstamps@yahoogroups.com, "othello159" <othello159@h...>
> > wrote:
> >
> >
> > > I have to revive this thread....
> > >
> > > Back when the unstable temp measurements first occurred changing
> > the power supply solved the problem.
> > >
> > > Now the little circuit (basic stamp 2 with an 0831 A/D converter
> > and a LM35 temp sensor, the stamp compares temps from two sensors and
> > switches a relays through a Darlington IC) is ready to go into its
> > final box (it controls the circulator pump for my hot water solar
> > system) and suddenly, as I connect the circuit to a car battery, its
> > permanent power source, I have these oscillations again.
> > .
> > .
> > .
> > This brings up a few questions. What else is on the power line ?
> > how long are the leads ? does it only happen when you are using your
> > cell phone, or the neighbor is on his HAM radio ? Are there electric
> > motors in the area....
> >
> > Getting a good isolation from any and everything on the power supply
> > is not terribly difficult, and may need a DC to DC converter to
> > really isolate you. Since you only have DC, you lose the simplicity
> > of a transformer. Also if you have a battery charger with some pulse
> > circuit, you may be creating the problems.
> >
> > Let us know more about your battery and charger. A power supply re-
> > design may be in order.
> >
> > Or, control of the pulse generator (desulphator?) where it runs 90%
> > of the time, you shut it off, take a temp reading, then turn it back
> > on ??
> >
> > (btw, I think I get brownie points if I gueseed this !)
> >
> >
> > > The countermeasures (see Allens note below) were still in place on
> > one LM35 ( I am using two) but it didn't make any difference, both
> > sensors were all over the place.
> > > So I connected a small cap across the battery terminal and
> > everything went quite and back to normal.
> > >
> > > So I proceed and connect the relays for the pump and the whole
> > circuit went wild again. Disconnect the relays and the sensors
> > readings go back to normal.
> > >
> > .
> > .
> > .
> > relays can be a PITA. there are many different types and voltages
> > for them.
> >
> >
> > As you mentioned pumps, those motors may be part of the problem.
> >
> > Consider this test. Since a relay on the logic side of your power
> > line filters will cause problems, it would be best if you kept your
> > logic separate from the power side.
> >
> > I'm assuming your pump relays are connected to the power side of any
> > line filters (caps or whatever for your logic)
> >
> > Also, since a relay switching will cause a spike, don't try to read
> > data for 20 seconds after you change state. that would eliminate any
> > spike from being part of your data.
> >
> > When designing a board with known PWM or other switching, we often
> > add a cap to the power supply of the micro to filter the spikes in
> > the power line. This would be right at the connection of the Stamp
> > or very close to it.
> >
> > Another question is what pins you are using to power the Stamp ? And
> > what is connected to the voltage regulator of the Stamp ? are you
> > powering other things with the on-board VR of the Stamp ?
> >
> >
> > Second, run a completely separate power line from your battery to
> > your board and then have only your output signal and ground to the
> > transistor that drives your relay. In other words, get your relay
> > board including mosfet or transistor out of the logic and over into
> > the power side.
> >
> > That way, only your logic signals are in your box.
> >
> > And possibly use an opto-isolator to control the relays. That way,
> > all your power is on one filtered line.
> >
> > Use shielded cable to your temperature sensor and don't connect
> > ground to both side, but keep the field sensor insulated from the
> > rest of the system by glass or plastic or something. that way, no
> > wire of your logic touches anything outside of the parts shown on
> > your schematic.
> >
> > This would mean to NOT let the sensor wire or shield or ground touch
> > any pipes or containers or anything.
> >
> >
> >
> >
> > > Second I am wondering if there are broader general design
> > guidelines to plan countermeasures against these gremlins into the
> > circuit right from the start (as opposed to what I do right now which
> > is deal with it when it happens). At this point I am afraid to move
> > the circuit to another room, who knows what will happen then...
> > .
> > .
> > .
> > Generally, there are two ways I look at things. Over design or under
> > design.
> >
> > If you over design, you use opto's all over the place and have a
> > completely isolated power source, all in a hermetically sealed
> > container that is rf shielded and temperature controlled.
> >
> > If you under design, you only need the very few parts that should
> > work and fix as you go.
> >
> > Most of us start with under design and then work up. It makes the
> > most cost and time effective way.
> >
> >
> > check out an op-amp amplifier circuit and then a op-amp instrument
> > schematic. basically the same thing in principal. vastly different
> > parts counts. The instrument connection uses both the 'in' and non-
> > in connections so as to allow a termperature shift to cancel each
> > other out (amung other things)
> >
> >
> > Dave
>
>
>
>
>
>
>
>
>
> Dave, I just answered Steve's questions but you raise a few more so here
we go.
>
> The test I mentioned was done with just a battery and my circuit, no 110V
power etc, no filters nothing.
>
> I use the Vin pin on the stamp to connect to my 12V car battery. I use a
78L05 to reduce that voltage for my A/D converters, nothing is connected to
the regulator of the stamp.
>
> And just as I am writing this to you, olala, I realize that my 78L05 VR
supplies the A/D converter as well as the relay with 5V and the switching is
done through the darlington which pulls the neg. side of the relay to
ground.
> Yeez, could that be a conflict area???
>
>
> Dave I will digest your other questions and respond soon.
>
> thanks for the help
>
> Uwe
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
> Yahoo! Groups Links
>
>
>
>
>
+5, you can send 6 volts to 12 volts to Vin.
Vin drives the on-module regulator, which gives
+5 volts to the rest of the module. You can
then take a very little current (< 100 mA)
FROM the VDD pin -- but it's not a good idea.
(This works really well with a 9-volt battery
connected to Vin by the way, in really low-power
situations)
The chip is built so that you CAN drive VDD directly
with +5 volts without making the on-module
regulator unhappy. In this case, leave Vin open.
--- In basicstamps@yahoogroups.com, "SB" <steve.brady@r...> wrote:
> possibly a faulty regulator?!
>
> I can't remember which is which...but you have one power pin on
the stamp
> that you provide exactly +5V and it runs there. Then there's
another pin
> that takes something a bit less regulated (can someone confirm
that?)
> Anyhow, if you have a power supply, maybe provide power with that
instead of
> the regulator.
> Also, I'm guessing you have a couple caps for setting up your
> regulator....check these and make sure your solder joints are good.
>
> As far as the relay....you did say you had the problem before
connecting the
> relay so the coil kicking dirt on to your ground plane isn't as
much an
> issue. Might've missed that..I'm not sure.
>
> without the relay...were you still using the darlington?
>
> Is the stamp powered for any length of time before this happens?
(thermal
> issues?)
>
>
>
Original Message
> From: "othello159" <othello159@h...>
> To: <basicstamps@yahoogroups.com>
> Sent: Thursday, May 20, 2004 2:11 PM
> Subject: [noparse][[/noparse]basicstamps] Re: unstable temp measurement
>
>
> > --- In basicstamps@yahoogroups.com, "Dave Mucha"
<davemucha@j...> wrote:
> > > --- In basicstamps@yahoogroups.com, "othello159"
<othello159@h...>
> > > wrote:
> > >
> > >
> > > > I have to revive this thread....
> > > >
> > > > Back when the unstable temp measurements first occurred
changing
> > > the power supply solved the problem.
> > > >
> > > > Now the little circuit (basic stamp 2 with an 0831 A/D
converter
> > > and a LM35 temp sensor, the stamp compares temps from two
sensors and
> > > switches a relays through a Darlington IC) is ready to go into
its
> > > final box (it controls the circulator pump for my hot water
solar
> > > system) and suddenly, as I connect the circuit to a car
battery, its
> > > permanent power source, I have these oscillations again.
> > > .
> > > .
> > > .
> > > This brings up a few questions. What else is on the power
line ?
> > > how long are the leads ? does it only happen when you are
using your
> > > cell phone, or the neighbor is on his HAM radio ? Are there
electric
> > > motors in the area....
> > >
> > > Getting a good isolation from any and everything on the power
supply
> > > is not terribly difficult, and may need a DC to DC converter to
> > > really isolate you. Since you only have DC, you lose the
simplicity
> > > of a transformer. Also if you have a battery charger with
some pulse
> > > circuit, you may be creating the problems.
> > >
> > > Let us know more about your battery and charger. A power
supply re-
> > > design may be in order.
> > >
> > > Or, control of the pulse generator (desulphator?) where it
runs 90%
> > > of the time, you shut it off, take a temp reading, then turn
it back
> > > on ??
> > >
> > > (btw, I think I get brownie points if I gueseed this !)
> > >
> > >
> > > > The countermeasures (see Allens note below) were still in
place on
> > > one LM35 ( I am using two) but it didn't make any difference,
both
> > > sensors were all over the place.
> > > > So I connected a small cap across the battery terminal and
> > > everything went quite and back to normal.
> > > >
> > > > So I proceed and connect the relays for the pump and the
whole
> > > circuit went wild again. Disconnect the relays and the sensors
> > > readings go back to normal.
> > > >
> > > .
> > > .
> > > .
> > > relays can be a PITA. there are many different types and
voltages
> > > for them.
> > >
> > >
> > > As you mentioned pumps, those motors may be part of the
problem.
> > >
> > > Consider this test. Since a relay on the logic side of your
power
> > > line filters will cause problems, it would be best if you
kept your
> > > logic separate from the power side.
> > >
> > > I'm assuming your pump relays are connected to the power side
of any
> > > line filters (caps or whatever for your logic)
> > >
> > > Also, since a relay switching will cause a spike, don't try to
read
> > > data for 20 seconds after you change state. that would
eliminate any
> > > spike from being part of your data.
> > >
> > > When designing a board with known PWM or other switching, we
often
> > > add a cap to the power supply of the micro to filter the
spikes in
> > > the power line. This would be right at the connection of the
Stamp
> > > or very close to it.
> > >
> > > Another question is what pins you are using to power the
Stamp ? And
> > > what is connected to the voltage regulator of the Stamp ? are
you
> > > powering other things with the on-board VR of the Stamp ?
> > >
> > >
> > > Second, run a completely separate power line from your battery
to
> > > your board and then have only your output signal and ground to
the
> > > transistor that drives your relay. In other words, get your
relay
> > > board including mosfet or transistor out of the logic and over
into
> > > the power side.
> > >
> > > That way, only your logic signals are in your box.
> > >
> > > And possibly use an opto-isolator to control the relays. That
way,
> > > all your power is on one filtered line.
> > >
> > > Use shielded cable to your temperature sensor and don't connect
> > > ground to both side, but keep the field sensor insulated from
the
> > > rest of the system by glass or plastic or something. that
way, no
> > > wire of your logic touches anything outside of the parts shown
on
> > > your schematic.
> > >
> > > This would mean to NOT let the sensor wire or shield or ground
touch
> > > any pipes or containers or anything.
> > >
> > >
> > >
> > >
> > > > Second I am wondering if there are broader general design
> > > guidelines to plan countermeasures against these gremlins into
the
> > > circuit right from the start (as opposed to what I do right
now which
> > > is deal with it when it happens). At this point I am afraid to
move
> > > the circuit to another room, who knows what will happen
then...
> > > .
> > > .
> > > .
> > > Generally, there are two ways I look at things. Over design
or under
> > > design.
> > >
> > > If you over design, you use opto's all over the place and have
a
> > > completely isolated power source, all in a hermetically sealed
> > > container that is rf shielded and temperature controlled.
> > >
> > > If you under design, you only need the very few parts that
should
> > > work and fix as you go.
> > >
> > > Most of us start with under design and then work up. It makes
the
> > > most cost and time effective way.
> > >
> > >
> > > check out an op-amp amplifier circuit and then a op-amp
instrument
> > > schematic. basically the same thing in principal. vastly
different
> > > parts counts. The instrument connection uses both the 'in'
and non-
> > > in connections so as to allow a termperature shift to cancel
each
> > > other out (amung other things)
> > >
> > >
> > > Dave
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > Dave, I just answered Steve's questions but you raise a few more
so here
> we go.
> >
> > The test I mentioned was done with just a battery and my
circuit, no 110V
> power etc, no filters nothing.
> >
> > I use the Vin pin on the stamp to connect to my 12V car battery.
I use a
> 78L05 to reduce that voltage for my A/D converters, nothing is
connected to
> the regulator of the stamp.
> >
> > And just as I am writing this to you, olala, I realize that my
78L05 VR
> supplies the A/D converter as well as the relay with 5V and the
switching is
> done through the darlington which pulls the neg. side of the relay
to
> ground.
> > Yeez, could that be a conflict area???
> >
> >
> > Dave I will digest your other questions and respond soon.
> >
> > thanks for the help
> >
> > Uwe
> >
> >
> >
> > To UNSUBSCRIBE, just send mail to:
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> > from the same email address that you subscribed. Text in the
Subject and
> Body of the message will be ignored.
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> >
> >
> >
> >
> >
>
> And yes there is a diode and a small cap on the relay.
>
> The relay is switched through a Darlington array (ULN 2803) which
is activated through the stamp.
>
<snip>
>
> Currently everything works just fine until I plug in the relay at
which point the circuit goes wild, even when the relay doesn't
switch. So just the coil being connected to the ULN2803 downstream
from the stamp must do something to the circuit. I would have said it
probably receives signals from my answering machine but that was off-
[noparse]:)[/noparse]
>
> regards Uwe
Check the connections for the ULN2830, posssibley breadboard them
external to all stamp power. The ULN2803 can have 10k resistors
between the Stamp and the inputs. common ground for the power.
But, you can connect the battery directly to the relays, then to the
darlington and then to ground. Remember the darlington is a NPN
device. Also, the relays do not need to be on the same voltage
regulator. In fact a seperate VR might offer much less noise in the
system.
Also check the Voltage regulator to see how hot it is getting. if
there is too much drain, then it will shut itself off and the voltage
will drop.
But, it sounds like you are getting closer to the solution.
Can you offer more information regarding the small cap on the
relay ?
Dave
>
> And just as I am writing this to you, olala, I realize that my 78L05 VR supplies the A/D converter as well as the relay with 5V and the switching is done through the darlington which pulls the neg. side of the relay to ground.
> Yeez, could that be a conflict area???
>
I had a hunch and breadboarded from the stamps output pin a separate Darlington transistor followed by the relay all powered by a separate little power supply but common ground to my main stamp PC board.
And now the readings are stable.
Somehow having the A/D converters powered by a small VR which also powered the Darlington and the relay didn't work.
Gremlins!
So I will simply build a separate relay board, that should do it.
Until I connect the pump motor of course, a PWM DC motor, you will probably hear from me then...
73 Uwe