Below is the schematic for my home-built bat detector, which is very similar to the Enhanced simple bat detector from Tony Messina, except for the pre-amplifier and the headphone amplifier.
For the pre-amplifier I chose to use two simple transistor stages instead of the two original opamps. For the headphone amplifier I used a LM386, because I want to use low-impedance headphones instead of a high-impedance earpiece.

I also have some experimental, ultra-simple, designs here.

Frequency division detector parts

From the left to the right, it contains:
(Click here for an ugly handdrawn schematic)

The schematic is split up in two parts, the pre-amplifier (left) and the rest of the circuit (right):

Across the supply I connected a 100uF capacitor for noise reduction and power stabilisation (not shown on the picture).
I used 4 1.5V penlite batteries for this circuit. As far as I can remember the circuit draws about 12 mA of current, so it should be able to run over 160 hours on alkaline batteries.
I soldered the circuit on a piece of single solder island perforated board and put it in a case slightly larger than a TV remote control. The batteries take up about half the space.

Future enhancements

This page was last updated Tuesday, December 28, 1999