>"Peter L. Peres" writes:
>>You cannot use a pullup, you have to use a pulldown (1k should work). Do
>>get the LM324 data sheet if you do not have it.

Sorry for being cryptic. The LM324 will not pull the output down to GND
(it cannot sink current when this happens). Therefore a hysteresis
positive feedback resistor cannot be used when the input is only 65mV
unless a pulldown is used at the output of the LM324. With the pulldown
the output will go down to 0V and so you can use a hysteresis resistor. If
you look in the datasheet you will see that it can only sink a few uA at
200mV Vo and 15V supply. If you look at the internal schematic you will
see immediately why this is so. It is probably better if you make your
circuit work without hysteresis.

You need about 60dB gain and the amp will be suitable up to about 1kHz,
with a 1k pulldown and 500k hysteresis resistor I think. If you do not use
hysteresis then forget about the pulldown too.

Peter

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