I have made a detector based on NE612 with 4046 oscillator and it works fine.
Here is a simple detector with switching mixer:
**broken link removed**
It uses 74HCU04 inverter as amplifier and oscillator! I modified it to use electret microphone.
I removed the differential transistor pair, connected the microphone to one inverter, after that another inverter to make 180 degrees phase shift.
It runs about 50 hours with two Nimh batteries in series
I am using it to listen at fixed 30kHz frequency the Northern bat which is the most common species in Helsinki.
Here is a simple detector with switching mixer:
**broken link removed**
It uses 74HCU04 inverter as amplifier and oscillator! I modified it to use electret microphone.
I removed the differential transistor pair, connected the microphone to one inverter, after that another inverter to make 180 degrees phase shift.
It runs about 50 hours with two Nimh batteries in series
I am using it to listen at fixed 30kHz frequency the Northern bat which is the most common species in Helsinki.
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