Hello all
I am working on an op amp circuit, for high resolution decibel measurement. But I have been having some trouble getting the wanted behavior.
I want to use digi pots to control the gains on the cascading op amps and to measure the amplitude. The final signal will be feed into an micro, where I will scan through the gains to find the most relevant range. Later on I intend to add an analog multiplexer so i can sample multiple microphones, but I don’t think that will make much of a difference to this part of the circuit.
I’m currently using a single power rail and I aim to make the most of my ADC hence a rectifier. My other reason for using a rectifier was to avoid problems of instability only using a single supply. But that might be worthy as most of the resolution comes from the gain control?
Here are the things I have tried and the problems found
In simulation a combination of an inverting amp and super diode worked, but only with a negative supply. In this case using a 9v battery; in practice the voltage follower didn’t work (using LM324), it gave +3.92v while the voltage divider was altered to -.35&8.76 vs 4.5&-4.5 without being connected. Showing final signal below
.
I half tried the two batteries in series trick, hence a battery grounded on the high side. The backwards battery quickly heated up the op amp! I don’t see how a second battery on the positive side would make a difference. could add MAX232 but they are expensive. Creating negative voltages
Probably the most successful circuit I tried was the following, even though it half works for all the wrong reasons. Practically the signal ended up being a little in the negatives, I assume this is because i’m using the op amps outside of their intended use. Trying to see the ADC readings over serial I saw a wave form, but the scope was a mess from the serial communication, I lost sight of any waveform .The output didn’t change when i turned the input signal off, which is never a good sign.
I don’t have a lot of experience with op amps, so any advice is welcome. Hopefully I can get through this before mid semester break is over. Thanks
I am working on an op amp circuit, for high resolution decibel measurement. But I have been having some trouble getting the wanted behavior.
I want to use digi pots to control the gains on the cascading op amps and to measure the amplitude. The final signal will be feed into an micro, where I will scan through the gains to find the most relevant range. Later on I intend to add an analog multiplexer so i can sample multiple microphones, but I don’t think that will make much of a difference to this part of the circuit.
I’m currently using a single power rail and I aim to make the most of my ADC hence a rectifier. My other reason for using a rectifier was to avoid problems of instability only using a single supply. But that might be worthy as most of the resolution comes from the gain control?
Here are the things I have tried and the problems found
- I couldn't put the super diode before any amplification, because even super diodes need to saturate i suppose
- It didn't work when I did it the other way around; the output static and a square wave after the first amp. I tried to follow the circuit suggested here, maybe its just the specific amp?
In simulation a combination of an inverting amp and super diode worked, but only with a negative supply. In this case using a 9v battery; in practice the voltage follower didn’t work (using LM324), it gave +3.92v while the voltage divider was altered to -.35&8.76 vs 4.5&-4.5 without being connected. Showing final signal below
I half tried the two batteries in series trick, hence a battery grounded on the high side. The backwards battery quickly heated up the op amp! I don’t see how a second battery on the positive side would make a difference. could add MAX232 but they are expensive. Creating negative voltages
Probably the most successful circuit I tried was the following, even though it half works for all the wrong reasons. Practically the signal ended up being a little in the negatives, I assume this is because i’m using the op amps outside of their intended use. Trying to see the ADC readings over serial I saw a wave form, but the scope was a mess from the serial communication, I lost sight of any waveform .The output didn’t change when i turned the input signal off, which is never a good sign.
I don’t have a lot of experience with op amps, so any advice is welcome. Hopefully I can get through this before mid semester break is over. Thanks