There is not much detail available for these modules and as I wanted to do something a little different, I needed to know a bit more.
To that end I traced out the circuit from a module so I could adapt it for my use. Here is the circuit in case anyone else wants to know.
There are several different ones available, but all appear to use LM393 and are very similar circuit wise.
This particular one is the Jaycar XC4438 which is widely available.
The main difference I have found are:
- some do not provide an analogue output
- some do not use the second part of the LM393 and drive the output LED from pin 1 along with the digital output (LED connected to ground)
- some have a 50k pot (not 100k)
- some have a small capacitor across the power rails (this one does not, but should have).
The output of the LM393 is open collector with R1 providing the pull-up. The output is HIGH until an input above the threshold is reached, when it goes LOW. It is only LOW for the duration that this input signal remains above the threshold - if it is fed with a steady tone, then the output pulses at that same frequency.
The analogue output is raw signal from the microphone with a DC bias - no amplification and no buffering.
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