Electronic – Microphone peak detector circuit no signal response


I have built a peak detector circuit using op-amps/comparators to amplify the signal from an electret microphone, hold the peak signal and create a sharp logic edge when a peak is detected to be sent to a microcontroller.

I have built the circuit as follows setting up OA1 as a non inverting amplifier with a gain of 1000, but the voltage out from the OA1 remains fixed at about 4.5V no matter how much noise I make into the microphone. The comparator part of the circuit is outputting approximately 2V low and 5V high depending on how I set the potentiometer. All the components appear to be working.


simulate this circuit – Schematic created using CircuitLab

Best Answer

The LM1458 is an op amp, and is not designed to be used as a comparator. The Texas Instruments datasheet specifies a minimum voltage of 6V. The datasheet also says that, when powered from +/-15V, the output can only typically reach +/-14V. The device does not have a rail-to-rail output. In your application, it is doing all it can, but there is not enough supply voltage for it to function properly. Same for the amplifier stage.

Also note that only the top half of the AC waveform generated by your microphone is getting through the op amp. Since there is no negative supply, the op-amp output saturates at its minimum output voltage for any negative input signal. That does not matter much for this type of circuit, but it is something to be aware of.

Some things to try are:

  • use an op amp that is rated to run from a +5V single supply

  • increase your supply voltage

  • use a comparator instead of an op-amp for the output