Zener diode for piezo sensor voltage regulator
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Posts: 46,084
Evening all:
I have one of those MSI piezo sensors (p/n#0-1002794-1 at digikey) I put it
on my o-scope and tapped it, it briefly outputs 40+ volts output/5mS or so.
I want to read this piezo ouput with the BS2, I've rigged up a 5.1 v zener
diode with a 220 ohm resistor to so it doesn't go past 5 volts and mess up
my LTC1298 ADC.
This doesn't work.
I want to read this piezo output with my BS2 with the LTC1298 ADC.
Anyone got any ideas?
Thanks,
Mark
I have one of those MSI piezo sensors (p/n#0-1002794-1 at digikey) I put it
on my o-scope and tapped it, it briefly outputs 40+ volts output/5mS or so.
I want to read this piezo ouput with the BS2, I've rigged up a 5.1 v zener
diode with a 220 ohm resistor to so it doesn't go past 5 volts and mess up
my LTC1298 ADC.
This doesn't work.
I want to read this piezo output with my BS2 with the LTC1298 ADC.
Anyone got any ideas?
Thanks,
Mark
Comments
>on my o-scope and tapped it, it briefly outputs 40+ volts output/5mS or so.
>
>I want to read this piezo ouput with the BS2, I've rigged up a 5.1 v zener
>diode with a 220 ohm resistor to so it doesn't go past 5 volts and mess up
>my LTC1298 ADC.
>
>This doesn't work.
>
>I want to read this piezo output with my BS2 with the LTC1298 ADC.
Hi Mark,
Look at the MSI circuit app notes:
http://www.measurementspecialties.com/PART8-INT.pdf
Zener diodes are very leaky, and would quickly dissipate the charge
generated by the impact.
I would leave out the zener diode, and instead protect the input to
the LTC1298 with a resistor and a small capacitor:
X> 20k
+
o---/\/\---LTC1298 input 1
|
| 20k
MSI o---/\/\--- P0
|
=== ~100pf capacitor
|
-
o
common
The 100pf capacitor acts as a voltage divider with the internal
capacitance of the sensor. Adjust the capacitor to set the
sensitivity, larger capacitor for a lower voltage.
The input can also be connected to pin P0 on the stamp, as shown. P0
can sense a 0-1 binary level if that is all you are interested in,
without needing the LTC1298. Occasionally, P0 can be switched to an
output to reset the circuit, because it will tend to drift.
Alternatively, suppress drift by putting a 22megohm resistor in
parallel with the 100pf capacitor.
You can turn it into a "peak detector" by inserting a low-leakage
switching diode (1N4148) at the "X>". PO has to be turned into a low
output briefly to reset the circuit for each pulse. Increasing the
value of the capacitor up to >>100pf will turn the circuit into a
simple "charge integrator".
Be careful if you build this on a white breadboard. The capacitance
between nodes is >100 pf, which can cause some unexpected problems.
For better results, put an op-amp in the circuit. The MSI app notes
have examples. What do you want to accomplish?
Tracy Allen
electronically monitored ecosystems
http://www.emesystems.com
to play in your system... are you trying to read a varying
voltage from the piezo unit? or Just on/off signals?
You will likely have to rectify and filter the piezo
output to tame it for the ADC - not just upper voltage
limit. The piezo output is AC.
You might try a diode + capacitor.
piezo diode cap
---XXX-->|---|--->
| = out to scope
|--->
Since you've got a scope look at the output accross the
capacitor - try .01 uf to start...
There are a lot of variables depending on what you are
trying to do... how fast you need to detect signal
change etc...
You can put a zener diode across the capacitor to clamp
the upper voltage; the current coming from the piezo
unit is quite low...
If this doesn't help try and be more specific as to what
you are trying to sense...
Thanks, premena
>>>
Date: Fri, 29 Dec 2000 18:00:57 -0800
From: "techno masai" <plunkettm@e...>
I have one of those MSI piezo sensors (p/n#0-1002794-1 at digikey) I put
it
on my o-scope and tapped it, it briefly outputs 40+ volts output/5mS or
so.
I want to read this piezo ouput with the BS2, I've rigged up a 5.1 v
zener
diode with a 220 ohm resistor to so it doesn't go past 5 volts and mess
up
my LTC1298 ADC.
This doesn't work.
I want to read this piezo output with my BS2 with the LTC1298 ADC.
<<<
________________________________________________________________
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Thanks for the link and circuit info.
The MSI manual will provide for some interesting weekend reading.
Thanks for the tip on the white board limitations, just went to Fry's an
electronics store where they had pen sort of thing, the ink is silver or
something and you can draw your own circuits with it and they were all sold
out. Sounds really cool though and could get past the white board problems,
I could just buy the bare perf board and just draw everything together, naw
somehow that'd be too easy.
Would like to be able to somehow characterize vibrations in conjunction with
a small lookup table programmed into the BS2 and then output different
commands depending on lookup table values.
These MSI piezo sensors are pretty economical and you could stick them on
things and get feedback to be used any number of ways, like maybe on a robot
leg or bumper.
BTW, is there some setting I can change on my Outlook Express so that the
ASCII char circuit dwgs line up properly, I can see the small 'o's in the
circuit is a junction, right?
Mark
Original Message
From: Tracy Allen <tracy@e...>
To: basicstamps@egroups.com <basicstamps@egroups.com>
Date: Saturday, December 30, 2000 12:53 AM
Subject: Re: [noparse][[/noparse]basicstamps] Zener diode for piezo sensor voltage regulator
>>I have one of those MSI piezo sensors (p/n#0-1002794-1 at digikey) I put
it
>>on my o-scope and tapped it, it briefly outputs 40+ volts output/5mS or
so.
>>
>>I want to read this piezo ouput with the BS2, I've rigged up a 5.1 v zener
>>diode with a 220 ohm resistor to so it doesn't go past 5 volts and mess up
>>my LTC1298 ADC.
>>
>>This doesn't work.
>>
>>I want to read this piezo output with my BS2 with the LTC1298 ADC.
>
>Hi Mark,
>
>Look at the MSI circuit app notes:
> http://www.measurementspecialties.com/PART8-INT.pdf
>
>Zener diodes are very leaky, and would quickly dissipate the charge
>generated by the impact.
>
>I would leave out the zener diode, and instead protect the input to
>the LTC1298 with a resistor and a small capacitor:
>
> X> 20k
> +
o---/\/\---LTC1298 input 1
> |
> | 20k
> MSI o---/\/\--- P0
> |
> === ~100pf capacitor
> |
> -
o
common
>
>The 100pf capacitor acts as a voltage divider with the internal
>capacitance of the sensor. Adjust the capacitor to set the
>sensitivity, larger capacitor for a lower voltage.
>
>The input can also be connected to pin P0 on the stamp, as shown. P0
>can sense a 0-1 binary level if that is all you are interested in,
>without needing the LTC1298. Occasionally, P0 can be switched to an
>output to reset the circuit, because it will tend to drift.
>Alternatively, suppress drift by putting a 22megohm resistor in
>parallel with the 100pf capacitor.
>
>You can turn it into a "peak detector" by inserting a low-leakage
>switching diode (1N4148) at the "X>". PO has to be turned into a low
>output briefly to reset the circuit for each pulse. Increasing the
>value of the capacitor up to >>100pf will turn the circuit into a
>simple "charge integrator".
>
>Be careful if you build this on a white breadboard. The capacitance
>between nodes is >100 pf, which can cause some unexpected problems.
>
>For better results, put an op-amp in the circuit. The MSI app notes
>have examples. What do you want to accomplish?
>
> Tracy Allen
> electronically monitored ecosystems
> http://www.emesystems.com
>
>
>
>
>
>
>
>
>
Gosh, hope nobody minds terribly that I'm kinda loading up the board here
with these piezo sensor replies. Although I'll be looking forward to
everyones replies I better stop answering replies to this piezo-zener thread
after this message.
Anywho, as I mentioned to Tracy I would like to be able to characterize
output from the piezo sensor as follows: vibration to ADC to programmed
lookup table in BS2.
If nothing else it could be used for kinda like a robot distress signal, if
the robot ran into something too hard maybe a bunch of LEDs might turn on.
Whereas under normal walking conditions a certain color LED would turn on
when each piezo sensored leg touched the ground.
So this would be pretty slow stuff. Just out of curiosity, how would speed
say 100 Hz or 1000 Hz affect a design scenario as I described above.
Thank you.
Mark
Original Message
From: s premena <premzee@j...>
To: basicstamps@egroups.com <basicstamps@egroups.com>
Date: Saturday, December 30, 2000 9:49 AM
Subject: [noparse][[/noparse]basicstamps] Re: Zener diode for piezo sensor voltage regulator
>It's not clear what function the ADC converter is supposed
>to play in your system... are you trying to read a varying
>voltage from the piezo unit? or Just on/off signals?
>
>You will likely have to rectify and filter the piezo
>output to tame it for the ADC - not just upper voltage
>limit. The piezo output is AC.
>
>You might try a diode + capacitor.
>
> piezo diode cap
>---XXX-->|---|--->
>| = out to scope
>
|--->
>
>Since you've got a scope look at the output accross the
>capacitor - try .01 uf to start...
>
>There are a lot of variables depending on what you are
>trying to do... how fast you need to detect signal
>change etc...
>
>You can put a zener diode across the capacitor to clamp
>the upper voltage; the current coming from the piezo
>unit is quite low...
>
>If this doesn't help try and be more specific as to what
>you are trying to sense...
>
>Thanks, premena
>
>>>>
> Date: Fri, 29 Dec 2000 18:00:57 -0800
> From: "techno masai" <plunkettm@e...>
>
>I have one of those MSI piezo sensors (p/n#0-1002794-1 at digikey) I put
>it
>on my o-scope and tapped it, it briefly outputs 40+ volts output/5mS or
>so.
>
>I want to read this piezo ouput with the BS2, I've rigged up a 5.1 v
>zener
>diode with a 220 ohm resistor to so it doesn't go past 5 volts and mess
>up
>my LTC1298 ADC.
>
>This doesn't work.
>
>I want to read this piezo output with my BS2 with the LTC1298 ADC.
>
><<<
>
>________________________________________________________________
>GET INTERNET ACCESS FROM JUNO!
>Juno offers FREE or PREMIUM Internet access for less!
>Join Juno today! For your FREE software, visit:
>http://dl.www.juno.com/get/tagj.
>
>
>
>
> that the ASCII char circuit dwgs line up properly, I can see the small
'o's
> in the circuit is a junction, right?
>
> Mark
I don't use Outlook, so I don't know if you can do this or not. However,
on my email program, the ASCII art appears OK if I change the font to
Courier (not Courier New or some other fancy font). You need to use a
font where all the characters are the same width.
Aaron
>electronics store where they had pen sort of thing, the ink is silver or
>something and you can draw your own circuits with it and they were all sold
>out. Sounds really cool though and could get past the white board problems,
>I could just buy the bare perf board and just draw everything together, naw
>somehow that'd be too easy.
Hi Mark,
Don't get me wrong--White breadboards are very useful and convenient.
The problems come with circuits that happen to be sensitive to small
extra capacitance. If a point in a circuit is affected in that way,
the usual trick is to bend up the leg of a chip and other parts that
supposed to connect at that point, and tack solder them together,
hanging in mid air.
>Would like to be able to somehow characterize vibrations in conjunction with
>a small lookup table programmed into the BS2 and then output different
>commands depending on lookup table values.
>
>If nothing else it could be used for kinda like a robot distress signal, if
>the robot ran into something too hard maybe a bunch of LEDs might turn on.
>
>Whereas under normal walking conditions a certain color LED would turn on
>when each piezo sensored leg touched the ground.
>
>So this would be pretty slow stuff. Just out of curiosity, how would speed
>say 100 Hz or 1000 Hz affect a design scenario as I described above.
The LTC1298 ADC + BASIC Stamp will not be able to capture a 100 hz
waveform and "analyze" it in real time. Is that what you mean by
the 100hz or 1000hz scenario? Digital Signal Processing takes
special high-horsepower chips.
That is not to say that you can't do something interesting with a
stamp. dsp with small letters. (1) Millisecond scale impacts could
be picked up by a comparator circuit, or by (2) a peak amplitude
detector, and you might even be able to (3) COUNT the frequency of
vibrations if they last long enough for the stamp to get around to
sampling them before they go away The low frequency response of the
piezo sensor can go below 1 hz, and a waveform that slow (4) could be
captured by the ADC for analysis of features, although I think the
stamp's lack of memory and speed would make that problematic.
BTW, I have used streamers of piezo film to detect slow wind movement
in caves, sort of like a sensitive insect "antenna".
-- Have fun in 01!
Tracy Allen
electronically monitored ecosystems
http://www.emesystems.com