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On the datasheet of the ADC:
"The analog input resistance is claimed to be 100 Mohms.
During an actual sample, the input resistance is temporarily a lot lower as the sampling capacitor is charged up so it is recommended that whatever you connect to the A/D have an output impedance of 10k or less for best accuracy."
"The analog input resistance is claimed to be 100 Mohms.
During an actual sample, the input resistance is temporarily a lot lower as the sampling capacitor is charged up so it is recommended that whatever you connect to the A/D have an output impedance of 10k or less for best accuracy."
"During an actual sample, the input resistance is temporarily a lot lower" then you explained why.
Hi!
So, I have tried to implement the circuit! I don't believe I got 100% perfect results, but I got results, to which I owe you 100%
!
This is my general input signal (disconnected to amplification circuit):
With a gain of 3 or 6 (can't remember exactly) I got this:
When I see the input signal it also seems to attenuated.
Only setting the gain to 30 I got to see decent amplification (but with lots of noise)!
The circuit I used was the following:
(I started with C1 = 2.2uF but changing to 10uF got me better results.. with 2.2uF I couldn't barely see cough signal! only when i tapped the piezo with my finger!)
Any hints? :|
So, I have tried to implement the circuit! I don't believe I got 100% perfect results, but I got results, to which I owe you 100%
!This is my general input signal (disconnected to amplification circuit):
With a gain of 3 or 6 (can't remember exactly) I got this:
When I see the input signal it also seems to attenuated.
Only setting the gain to 30 I got to see decent amplification (but with lots of noise)!
The circuit I used was the following:
(I started with C1 = 2.2uF but changing to 10uF got me better results.. with 2.2uF I couldn't barely see cough signal! only when i tapped the piezo with my finger!)
Any hints? :|
Attachments
Sorry! R1 was always 100k!
A piezo transducer has such a horrible frequency response that I have never used one as a speaker or microphone.
Since your opamp has no part number then we do not know if it has a very high input impedance and low input current so the 100k bias resistor can be increased to 1M or higher. Then you could try it.
Since your opamp has no part number then we do not know if it has a very high input impedance and low input current so the 100k bias resistor can be increased to 1M or higher. Then you could try it.
Sorry!
I have made this circuit for an eletromyography circuit and it worked nicely
Using OP07
Yes, try 1M as R1 in the preamp circuit.
Your preamp uses a single supply but your rectifier needs a dual polarity supply. Why don't you use a single opamp with a single supply for the fullwave rectifier? I use an MC33171 opamp that is a single opamp similar but better than an opamp in an LM324 or LM358. You could try a dual MC33172 opamp as the preamp plus rectifier if its noise in the preamp is not a problem.
Your preamp uses a single supply but your rectifier needs a dual polarity supply. Why don't you use a single opamp with a single supply for the fullwave rectifier? I use an MC33171 opamp that is a single opamp similar but better than an opamp in an LM324 or LM358. You could try a dual MC33172 opamp as the preamp plus rectifier if its noise in the preamp is not a problem.
Attachments
Sorry, you mean only try the circuit you attached? With the R1 in that schematic R1=1M?
Will it work LM358 for testing only? (I have it on the lab)
The fullwave rectifier circuit I posted should be fed from a low resistance to ground signal source like from a preamp opamp powered from a dual polarity supply. If an LM358 opamp is used for the fullwave rectifier and its input is capacitor-coupled from the output if the preamp then the input bias current of the LM358 will cause its input to float high and it will fail to work properly.
