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Signals crossover

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prprog

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I have built a circuit to amplifiy the signal from 2 piezo (using an Opamp). It work as expected. Using a Parallax Stamp I can read when each piezo is activate. No problem there. I added an ADC0831 to be able to read how hard the piezos were hit. For this application I don't need to know how hard each piezo was hit, an average will do. The problem is the signal cross over the other and I am not able to determine which one is active. I am sure is the way I connect the signals (A and B) to the ADC and to each pin (PIN 1 and PIN2), but cannot figure out how to make it work. How do I isolate each PIN signal (PIN 1 and PIN2) but be able to combined each signal for the ADC?


Thanks,
PRPROG
 
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You need to isolate each piezo output by multiplexing them (with a high switching rate) individually into the ADC. Do the signal combining after the ADC with the Stamp.

Or, use 2 separate ADCs.
 
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signal crossover

Thanks cowboybob for the quick reply.

I understand your answer...but could it be possible to isolate the signals without using a multiplexer?

Thanks,
prprog
 
Maybe if you can explain how the piezos are being used, there might be an isolation opportunity. I'm just not seeing any others at the moment.
 
If you want to share a processing circuit with more than one signal, then multiplexing is needed. The other option is to have separate, identical processing circuits for each signal.

If only one piezo is active at a time then you could add a comparator at each piezo output to detect which one has generated a signal.
 
If only one piezo is active at a time then you could add a comparator at each piezo output to detect which one has generated a signal.

Depending of how it is implemented, the measurement I mean, waiting for the comparator to say who, could cause loosing the chance of measuring the first part of the event. Am I right?
 
Depending of how it is implemented, the measurement I mean, waiting for the comparator to say who, could cause loosing the chance of measuring the first part of the event.
He stated he is already reading the signal so he's not missing anything. The comparator is just to tell him which piezo is generating the signal.
 
Yes, you are right. Sorry for not grasping the whole thing and posting instead.
 
I have built a circuit to amplifiy the signal from 2 piezo (using an Opamp). It work as expected. Using a Parallax Stamp I can read when each piezo is activate. No problem there. I added an ADC0831 to be able to read how hard the piezos were hit. For this application I don't need to know how hard each piezo was hit, an average will do. The problem is the signal cross over the other and I am not able to determine which one is active. I am sure is the way I connect the signals (A and B) to the ADC and to each pin (PIN 1 and PIN2), but cannot figure out how to make it work. How do I isolate each PIN signal (PIN 1 and PIN2) but be able to combined each signal for the ADC?


Thanks,
PRPROG

Following my own posting I realize that except for the signal crossover (sorry if this is not the correct term) everything work as expected. So I remember the way most of the keyboards (music) are design and try 2 diodes before they get to the ADC. Now I get full isolation , becuase the PIN1 and PIN2 , which detect if the signal is ON or OFF work as before , the ADC gets the signal A or signal B (or both) and signal A does not interfere with PIN 2 nor signal B interfere with PIN1. [probably I will have to increase the OpAmp amplification to compensate for the Diode drop].

Thanks a lot to all for your suggestions.

Prprog
 
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Following my own posting I realize that except for the signal crossover (sorry if this is not the correct term) everything work as expected. So I remember the way most of the keyboards (music) are design and try 2 diodes before they get to the ADC. Now I get full isolation , becuase the PIN1 and PIN2 , which detect if the signal is ON or OFF work as before , the ADC gets the signal A or signal B (or both) and signal A does not interfere with PIN 2 nor signal B interfere with PIN1. [probably I will have to increase the OpAmp amplification to compensate for the Diode drop].
I don't understand how the diodes help with (what I thought was) the initial problem of determining which piezo was hit. :confused:
 
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I don't understand how the diodes help with you (what I thought was) the initial problem of determining which piezo was hit. :confused:

When I run the signals without the ADC each signal is read separate by a different PIN in the Parallax Stamp. Then I add one ADC, and combine each signal into the same ADC. The signals cross over to each other PIN's (PIN 1 and PIN 2) . With the diodes each signal are kept independent (again) and still I can read then with just one ADC.

If you read my original posting the problem started when I add the ADC to read both signals with just one ADC.
 
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