Hi all,
I have been reading through lots of threads and articles as well as breadboarding some circuits without good results so since there are people here with much more knowledge than I, I'd like to get your input.
I have constructed a circuit that is receiving a sinewave at a fixed 76Hz. The whole idea is to measure the signal level. This signal starts out very small in the microvolt range and I amplify and bandpass filter it. I have a nice clean sinewave at this point. Next I capacitive couple the signal through an op amp which has a 5volt single supply so the end result is similar to half wave rectification and I end up with only the positive side of the original sinewave. Next stage I have a op amp configuration that can either attenuate or amplify the signal so it ends up near zero (10 to 20mV) and the peaks can go to 5volts. The final configuration is for a digital pot controlled by a microcontroller to adjust this circuit. On the perfboard I have a multi turn trimmer for testing purposes in this circuit and it works fine. In fact up to this point everything is working as needed. The last circuit is to take the signal and give a DC voltage equal to the peak value of the positive sinewave peaks (~10mV to 5V). I will feed this into an A/D on a PIC microcontroller.
The input to the peak detector is going to be anywhere from approximately 10mV to 5V. The 2 circuits I found and tried so far will not handle this range and the output is non-linear when the signal input is low. I tried the circuit using an LM393 published in many places on the web including on this forum because it states it will accept an input as low as 10mV but this circuit didn't work well as I described. With low signal inputs it was nonlinear (not accurate) and it would only go as high as approximately 2.5V. Someone else in another thread stated that they had issues with it when the signal frequency was below 1000Hz. I'm at 76Hz range.
The end device will not have a continuosly changing signal level such that it can be slow. In other words, it will be turned on, the signal level checked, then the sensor will be moved, then the signal level checked, etc. So it can be relatively slow. I hope I've given enough detail. Any suggestions are greatly appreciated.
Boattow
I have been reading through lots of threads and articles as well as breadboarding some circuits without good results so since there are people here with much more knowledge than I, I'd like to get your input.
I have constructed a circuit that is receiving a sinewave at a fixed 76Hz. The whole idea is to measure the signal level. This signal starts out very small in the microvolt range and I amplify and bandpass filter it. I have a nice clean sinewave at this point. Next I capacitive couple the signal through an op amp which has a 5volt single supply so the end result is similar to half wave rectification and I end up with only the positive side of the original sinewave. Next stage I have a op amp configuration that can either attenuate or amplify the signal so it ends up near zero (10 to 20mV) and the peaks can go to 5volts. The final configuration is for a digital pot controlled by a microcontroller to adjust this circuit. On the perfboard I have a multi turn trimmer for testing purposes in this circuit and it works fine. In fact up to this point everything is working as needed. The last circuit is to take the signal and give a DC voltage equal to the peak value of the positive sinewave peaks (~10mV to 5V). I will feed this into an A/D on a PIC microcontroller.
The input to the peak detector is going to be anywhere from approximately 10mV to 5V. The 2 circuits I found and tried so far will not handle this range and the output is non-linear when the signal input is low. I tried the circuit using an LM393 published in many places on the web including on this forum because it states it will accept an input as low as 10mV but this circuit didn't work well as I described. With low signal inputs it was nonlinear (not accurate) and it would only go as high as approximately 2.5V. Someone else in another thread stated that they had issues with it when the signal frequency was below 1000Hz. I'm at 76Hz range.
The end device will not have a continuosly changing signal level such that it can be slow. In other words, it will be turned on, the signal level checked, then the sensor will be moved, then the signal level checked, etc. So it can be relatively slow. I hope I've given enough detail. Any suggestions are greatly appreciated.
Boattow