digital voltmeter, 24v
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Posts: 46,084
I want to measure voltage around 24v. It could be more, upto maybe
around 30 volts, and could go all the way down to 0. So, how can I
do this? Really what I'm asking is, does anyone know of a A/D
converter capable of measuring in this range?
I've seen most measure upto around 5 volts, I just haven't been able
to find one that measures higher.
around 30 volts, and could go all the way down to 0. So, how can I
do this? Really what I'm asking is, does anyone know of a A/D
converter capable of measuring in this range?
I've seen most measure upto around 5 volts, I just haven't been able
to find one that measures higher.
Comments
depending on your requirements.
For example, a 5:1 voltage divider would convert 0-25V to 0-5V. Of
course, the resolution goes down too. So, say you have an 8 bit 5V
converter. That's 5/255V per step, but with the 5:1 divider you get
25/255V per step (which makes sense).
If you can't tolerate a voltage divider, you can use an op amp with a
gain < 1. This can have as high an input impedance as you like. Of
course, you need a voltage supply with some head room (say, 26V) if you
expect the op amp to output 24V. Be sure to get an op amp that can "go
to the negative rail" so you can use ground instead of a negative
supply.
Of course, you could make a 6:1 (or 1/6 gain) to measure to 30V, etc.
Hope that helps!
Al Williams
AWC
* Floating point A/D
http://www.al-williams.com/awce/pak9.htm
>
Original Message
> From: kiltjim [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=1bBI-TWtDbDcdiDfW-a_4bjLwC5VSY9xjLAJoJz6a1eP9FGDJhoMl2Brz6yrj2ThjcukXixu]kiltjim@a...[/url
> Sent: Saturday, March 08, 2003 10:24 AM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] digital voltmeter, 24v
>
>
> I want to measure voltage around 24v. It could be more, upto maybe
> around 30 volts, and could go all the way down to 0. So, how can I
> do this? Really what I'm asking is, does anyone know of a A/D
> converter capable of measuring in this range?
>
> I've seen most measure upto around 5 volts, I just haven't been able
> to find one that measures higher.
>
>
> 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.
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
>
>
>
>
since it sounds a lot simpler than the op amp, and I am not really
concerned with accuracy, since this is only used in estimation to
begin with.
However (and this is gonna sounds really stupid), how do i hook up a
voltage divider? I am not that great at circuit design, but if
somebody has a decent schematic and the math to go with it, I can
hook it up with no problem.
Thanks for the help,
Jim
--- In basicstamps@yahoogroups.com, "Al Williams" <alw@a...> wrote:
> Usually, you use an op amp with a fractional gain or a voltage
divider
> depending on your requirements.
>
> For example, a 5:1 voltage divider would convert 0-25V to 0-5V. Of
> course, the resolution goes down too. So, say you have an 8 bit 5V
> converter. That's 5/255V per step, but with the 5:1 divider you get
> 25/255V per step (which makes sense).
>
> If you can't tolerate a voltage divider, you can use an op amp with
a
> gain < 1. This can have as high an input impedance as you like. Of
> course, you need a voltage supply with some head room (say, 26V) if
you
> expect the op amp to output 24V. Be sure to get an op amp that
can "go
> to the negative rail" so you can use ground instead of a negative
> supply.
>
> Of course, you could make a 6:1 (or 1/6 gain) to measure to 30V,
etc.
>
> Hope that helps!
>
> Al Williams
> AWC
> * Floating point A/D
> http://www.al-williams.com/awce/pak9.htm
writes:
> All right, that sounds good. I like the idea of the voltage divider,
> since it sounds a lot simpler than the op amp, and I am not really
> concerned with accuracy, since this is only used in estimation to
> begin with.
>
> However (and this is gonna sounds really stupid), how do i hook up a
> voltage divider? I am not that great at circuit design, but if
> somebody has a decent schematic and the math to go with it, I can
> hook it up with no problem.
>
> Thanks for the help,
> Jim
>
Jim,
You correctly predicted the voltage divider will be much simpler that the
op-amp.
To change your 0 to 24 volts to 0 to 5 volts you do the following:
First, hopefully this will give you an idea of what you are doing......
Don't do this first one, it is only an explanation.
Connect 24 1k ohm resistors in series from ground to the voltage source. When
the source is at 24 volts, the voltage "above" the 5th resistor will be at 5
volts. I.e., at 24 volts each resistor will have 1 volt across it.
The actual circuit should be built as follows:
connect 5k ohms to and 19k ohms in series from ground to the voltage source.
The 5k resistor goes to ground. Now, when the voltage source is at 24 volts,
there will be 5v across the 5k resistor. When the voltage source is 12 volts,
there will be 2.5 volts across the 5k resistor....see the pattern?
Realistically, you may not easily be able to get a 5k and a 19k ohm resistor
unless you order 1% tolerance resistors, and still I am not sure if those
values are available. The bottom line is this, to get 5 volts when the supply
is at 24 volts, you want two resistors (or combination of resistors) that
will make a ratio of 3.8 to 1.
That is the amount of resistance from the supply to the output should be 3.8
times greater than the resistance from the output to ground (output being
where you will get 5v when the supply is 24 volts).
X = a resistor
see below
Voltage supply XXXXX19kohmsXXXXXXX outputXXXXXXX5kohmsXXXXXXXground
Hope my long winded explanation did more good than harm.
One more IMPORTANT point. whatever values or combination of values you use to
get your 3.8 to 1 ratio, make sure the total resistance is a minimum of 3000
ohms. Assuming you will be using standard 1/4 watt resistors. If your total
resistance is much less than 3000 ohms, the resistors will get too hot to
touch.
And for the math
Vsupply XXresistor_oneXXOUTPUTXXresistor_twoXX ground
The output voltage = Vsupply*resistor_two / (resistor_one+resistor_two)
And with some simple algebra
Vsupply = Vout(R1+R2) / R1
examples using 5k and 19k ohms:
Vout = 5v.....
5v(24kohms)/5kohms = 24 volts
Vout = 2.5 volts
2.5v(24kohms)/5kohms = 12volts
and so on.
Don't hesitate to write back if there is some point you don't understand. NO
SUCH THING AS A DUMB QUESTION, I ASK THEM ALL THE TIME!!!!!!!!!!!!
[noparse][[/noparse]Non-text portions of this message have been removed]
Just a quick question, what do you want to measure with your voltmeter
?. You need to set the total resistance of your voltage divider so it
doesn't "load" the voltage you are measuring too much.
Rob
Original Message
From: kiltjim [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=Gri-URFCWoPRSdQQXqaV8qFVsiX_GTYURozA8SsDyUfknmAx-CmTK-bKe3feogxeC0jjoaCEtkLLSQ]kiltjim@a...[/url
Sent: 09 March 2003 01:42
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Re: digital voltmeter, 24v
Alright, that sounds good. I like the idea of the voltage divider,
since it sounds a lot simpler than the op amp, and I am not really
concerned with accuracy, since this is only used in estimation to
begin with.
However (and this is gonna sounds really stupid), how do i hook up a
voltage divider? I am not that great at circuit design, but if
somebody has a decent schematic and the math to go with it, I can
hook it up with no problem.
Thanks for the help,
Jim
internal AVR ADC and need a signal between zero and five volts to represent
0 to 24 volts.
Pick up a pot and play with it , 20k should be good. Connect 24v to pin 1,
pin 3 to ground, and pin 2 (the wiper) to ground through a resistor. Measure
voltage between the pot and the resistor. Now turn the pot until you get
exactly five volts out when you put 24 volts in.
Turn off the power and measure resistance between the pot input and the
wiper output and across the while pot (they're usually not exactly what
they're rating says). You'll notice that the ratio is 5:24.
Now turn the power back on and vary the voltage input. If you apply 12
volts, you should get 2.5 volts out of the wiper. 6 volts gets you 1.25
volts, etc.
One warning - if you just hook the wiper to ground and use a meter to
measure, DONT turn the pot all the way to zero resistance. That'll be a
short and you'll fry the pot. Put another resistor between the wiper and
ground and take your measurements between the pot and the resistor. Then if
you go to zero resistance you won't smoke the poor thing.
Now just find two resistors that have a 5:24 resistance ratio. Put them in
series and measure the voltage in between the two - same thing! It can be
tough to find the right value resistors and even then you have tolerances
that'll probably not quite match the ratio you need. Thats why I like to use
pots instead. Make sure you get a multi-turn pot and not a single turn. The
single turns work but they're bloody hard to set properly. One tiny touch
and your ratio is way off.
My 'lectronic Newb site http://members.shaw.ca/pmeloy/
Original Message
From: "kiltjim" <kiltjim@a...>
To: <basicstamps@yahoogroups.com>
Sent: Saturday, March 08, 2003 5:41 PM
Subject: [noparse][[/noparse]basicstamps] Re: digital voltmeter, 24v
> Alright, that sounds good. I like the idea of the voltage divider,
> since it sounds a lot simpler than the op amp, and I am not really
> concerned with accuracy, since this is only used in estimation to
> begin with.
>
> However (and this is gonna sounds really stupid), how do i hook up a
> voltage divider? I am not that great at circuit design, but if
> somebody has a decent schematic and the math to go with it, I can
> hook it up with no problem.
>
> Thanks for the help,
> Jim
>
> --- In basicstamps@yahoogroups.com, "Al Williams" <alw@a...> wrote:
> > Usually, you use an op amp with a fractional gain or a voltage
> divider
> > depending on your requirements.
> >
> > For example, a 5:1 voltage divider would convert 0-25V to 0-5V. Of
> > course, the resolution goes down too. So, say you have an 8 bit 5V
> > converter. That's 5/255V per step, but with the 5:1 divider you get
> > 25/255V per step (which makes sense).
> >
> > If you can't tolerate a voltage divider, you can use an op amp with
> a
> > gain < 1. This can have as high an input impedance as you like. Of
> > course, you need a voltage supply with some head room (say, 26V) if
> you
> > expect the op amp to output 24V. Be sure to get an op amp that
> can "go
> > to the negative rail" so you can use ground instead of a negative
> > supply.
> >
> > Of course, you could make a 6:1 (or 1/6 gain) to measure to 30V,
> etc.
> >
> > Hope that helps!
> >
> > Al Williams
> > AWC
> > * Floating point A/D
> > http://www.al-williams.com/awce/pak9.htm
>
>
> 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.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
I have already a lot of knobs and leds with the use of 74hc165/74hc595 , now
I need more pots and faders for my midi-mixer.
3 in for knobs
3 out for leds
1 out for midi out
I can use dthe other 9 for pots or faders
Original Message
From: "Pat M" <pmeloy@s...>
To: <basicstamps@yahoogroups.com>
Sent: Sunday, March 09, 2003 12:11 PM
Subject: Re: [noparse][[/noparse]basicstamps] Re: digital voltmeter, 24v
> Any potentiometer is actually a voltage divider. Lets say you use the
> internal AVR ADC and need a signal between zero and five volts to
represent
> 0 to 24 volts.
>
> Pick up a pot and play with it , 20k should be good. Connect 24v to pin 1,
> pin 3 to ground, and pin 2 (the wiper) to ground through a resistor.
Measure
> voltage between the pot and the resistor. Now turn the pot until you get
> exactly five volts out when you put 24 volts in.
>
> Turn off the power and measure resistance between the pot input and the
> wiper output and across the while pot (they're usually not exactly what
> they're rating says). You'll notice that the ratio is 5:24.
>
> Now turn the power back on and vary the voltage input. If you apply 12
> volts, you should get 2.5 volts out of the wiper. 6 volts gets you 1.25
> volts, etc.
>
> One warning - if you just hook the wiper to ground and use a meter to
> measure, DONT turn the pot all the way to zero resistance. That'll be a
> short and you'll fry the pot. Put another resistor between the wiper and
> ground and take your measurements between the pot and the resistor. Then
if
> you go to zero resistance you won't smoke the poor thing.
>
> Now just find two resistors that have a 5:24 resistance ratio. Put them in
> series and measure the voltage in between the two - same thing! It can be
> tough to find the right value resistors and even then you have tolerances
> that'll probably not quite match the ratio you need. Thats why I like to
use
> pots instead. Make sure you get a multi-turn pot and not a single turn.
The
> single turns work but they're bloody hard to set properly. One tiny touch
> and your ratio is way off.
>
>
>
>
>
>
> My 'lectronic Newb site http://members.shaw.ca/pmeloy/
>
Original Message
> From: "kiltjim" <kiltjim@a...>
> To: <basicstamps@yahoogroups.com>
> Sent: Saturday, March 08, 2003 5:41 PM
> Subject: [noparse][[/noparse]basicstamps] Re: digital voltmeter, 24v
>
>
> > Alright, that sounds good. I like the idea of the voltage divider,
> > since it sounds a lot simpler than the op amp, and I am not really
> > concerned with accuracy, since this is only used in estimation to
> > begin with.
> >
> > However (and this is gonna sounds really stupid), how do i hook up a
> > voltage divider? I am not that great at circuit design, but if
> > somebody has a decent schematic and the math to go with it, I can
> > hook it up with no problem.
> >
> > Thanks for the help,
> > Jim
> >
> > --- In basicstamps@yahoogroups.com, "Al Williams" <alw@a...> wrote:
> > > Usually, you use an op amp with a fractional gain or a voltage
> > divider
> > > depending on your requirements.
> > >
> > > For example, a 5:1 voltage divider would convert 0-25V to 0-5V. Of
> > > course, the resolution goes down too. So, say you have an 8 bit 5V
> > > converter. That's 5/255V per step, but with the 5:1 divider you get
> > > 25/255V per step (which makes sense).
> > >
> > > If you can't tolerate a voltage divider, you can use an op amp with
> > a
> > > gain < 1. This can have as high an input impedance as you like. Of
> > > course, you need a voltage supply with some head room (say, 26V) if
> > you
> > > expect the op amp to output 24V. Be sure to get an op amp that
> > can "go
> > > to the negative rail" so you can use ground instead of a negative
> > > supply.
> > >
> > > Of course, you could make a 6:1 (or 1/6 gain) to measure to 30V,
> > etc.
> > >
> > > Hope that helps!
> > >
> > > Al Williams
> > > AWC
> > > * Floating point A/D
> > > http://www.al-williams.com/awce/pak9.htm
> >
> >
> > 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.
> >
> >
> > Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
> >
> >
>
>
> 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.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
i am building a midi-controller , and have 1 question.????
who knows how I can use more pots with stamp2
I have already a lot of knobs and leds with the use of 74hc165/74hc595 , now
I need more pots and faders for my midi-mixer.
already ports in use:
3 in for knobs
3 out for leds
1 out for midi out
I can use the other 9 for pots or faders but wanted more faders/pots ????
won't do it again. However, you might enjoy reading:
http://www.wd5gnr.com/basiccir.htm
Which talks about voltage dividers among other things. I need to draw
some pictures for that article I suppose :-)
Al Williams
AWC
* Floating point A/D
http://www.al-williams.com/awce/pak9.htm
>
Original Message
> From: kiltjim [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=oOIXJ36153nZ_BYbn3DRzG7fdtfgQaKECzt5owxTPTP1HvFtD_aN4XhWJV76KAIVjXfO5zn4Xg]kiltjim@a...[/url
> Sent: Saturday, March 08, 2003 7:42 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Re: digital voltmeter, 24v
>
>
> Alright, that sounds good. I like the idea of the voltage divider,
> since it sounds a lot simpler than the op amp, and I am not really
> concerned with accuracy, since this is only used in estimation to
> begin with.
>
> However (and this is gonna sounds really stupid), how do i hook up a
> voltage divider? I am not that great at circuit design, but if
> somebody has a decent schematic and the math to go with it, I can
> hook it up with no problem.
>
> Thanks for the help,
> Jim
>
> --- In basicstamps@yahoogroups.com, "Al Williams" <alw@a...> wrote:
> > Usually, you use an op amp with a fractional gain or a voltage
> divider
> > depending on your requirements.
> >
> > For example, a 5:1 voltage divider would convert 0-25V to 0-5V. Of
> > course, the resolution goes down too. So, say you have an 8 bit 5V
> > converter. That's 5/255V per step, but with the 5:1 divider you get
> > 25/255V per step (which makes sense).
> >
> > If you can't tolerate a voltage divider, you can use an op amp with
> a
> > gain < 1. This can have as high an input impedance as you like. Of
> > course, you need a voltage supply with some head room (say, 26V) if
> you
> > expect the op amp to output 24V. Be sure to get an op amp that
> can "go
> > to the negative rail" so you can use ground instead of a negative
> > supply.
> >
> > Of course, you could make a 6:1 (or 1/6 gain) to measure to 30V,
> etc.
> >
> > Hope that helps!
> >
> > Al Williams
> > AWC
> > * Floating point A/D http://www.al-williams.com/awce/pak9.htm
>
>
> 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.
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
>
>
>
>
:-) You can tell I'm procrastinating this morning!
Al Williams
AWC
* NEW kits
http://www.al-williams.com/kits.htm
>
Original Message
> From: kiltjim [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=TjBPcc4m7be5eGpUDDcayszbjbXQkKTN53ixG3yXGThOiaSOc1StoXSycfj4H9QQP2Vypj8xgVwX]kiltjim@a...[/url
> Sent: Saturday, March 08, 2003 7:42 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Re: digital voltmeter, 24v
>
>
> Alright, that sounds good. I like the idea of the voltage divider,
> since it sounds a lot simpler than the op amp, and I am not really
> concerned with accuracy, since this is only used in estimation to
> begin with.
>
> However (and this is gonna sounds really stupid), how do i hook up a
> voltage divider? I am not that great at circuit design, but if
> somebody has a decent schematic and the math to go with it, I can
> hook it up with no problem.
>
> Thanks for the help,
> Jim
>
> --- In basicstamps@yahoogroups.com, "Al Williams" <alw@a...> wrote:
> > Usually, you use an op amp with a fractional gain or a voltage
> divider
> > depending on your requirements.
> >
> > For example, a 5:1 voltage divider would convert 0-25V to 0-5V. Of
> > course, the resolution goes down too. So, say you have an 8 bit 5V
> > converter. That's 5/255V per step, but with the 5:1 divider you get
> > 25/255V per step (which makes sense).
> >
> > If you can't tolerate a voltage divider, you can use an op amp with
> a
> > gain < 1. This can have as high an input impedance as you like. Of
> > course, you need a voltage supply with some head room (say, 26V) if
> you
> > expect the op amp to output 24V. Be sure to get an op amp that
> can "go
> > to the negative rail" so you can use ground instead of a negative
> > supply.
> >
> > Of course, you could make a 6:1 (or 1/6 gain) to measure to 30V,
> etc.
> >
> > Hope that helps!
> >
> > Al Williams
> > AWC
> > * Floating point A/D http://www.al-williams.com/awce/pak9.htm
>
>
> 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.
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
>
>
>
>