Digital Frequency Division Bat Detector: Construction and testing


The circuit is very simple with few components and can be built on a small piece of Veroboard (stripboard).  Don't solder anything in until the components are all in place!

This is the top view of the veroboard (stripboard) layout.  All tracks under ICs are to be broken as shown here (top right of this figure).
You will need to cut and file the veroboard to fit into your case - ours measured only 104mm * 62 mm.

  • Start by placing the IC sockets - don't solder them in yet, just dot two corner pins with solder to hold them in place. Make the breaks in the track under the IC's using a small drill bit. Check carefully that there is no connection across the break.
  • Then place the straight wire links.  These can be made with tinned copper wire of about 24SWG.  Pull it until it stretches a bit before using it - that way you will get nice straight bits of wire.
  • Next the resistors and capacitors can be added.  Bend the legs to hold them in place.
  • By now the board should be almost complete.  Compare it with the diagram to make sure the positions are correct, and that nothing has been left out.
  • It has!  Now place the off-board connector pins marked x, and the single bent wire link. This needs to be an insulated wire as it lies across a link.
  • Wire up the battery connector and jack socket. Ours included switch contacts to turn on the detector when the phones were plugged in. (see photo)
  • Now you can solder all the components in place, and trim the wire ends off.   Check for any solder bridges or dry joints.


Now power the circuit up, and check the current drain.  There shouldn't be much - no IC's in place yet! Remove the power.

Connect the off-board components, using short lengths of twisted wire. Plug a set of headphones into the jack. Put the LM386 in and connect the battery.  You should hear a slight hiss in the phones, and maybe some hum if you touch pin 3 with a piece of wire.  The current drain will increase. 

Disconnect the battery and place the other two IC's.  Reconnect the battery and test the detector with some ultrasound.

Haven't got a tame bat?  Rubbing your hands together, snapping your fingers, jangling keys or rubbing a nylon jacket all make sounds your detector should pick up.  Now that it's working, fit it into its case, and look forward to lots of late nights as you use your detector in the field!

The finished detector should look like this:

finished detector

Pin configuration of IC's, and parts list

Hex Inverter


Audio amplifier


4069: never leave CMOS gate inputs unconnected as static charge can blow up the IC.  Pin 13 is connected to +Vdd



4024: RESET (active high) needs to be connected to 0V to allow counter operation



LM386: The supply needs to be decoupled with a capacitor (C6) wired closely to the supply pins.

Parts list for Digital Bat Detector
Resistors: all 0.25W Value Capacitors Value MISC
R1 10k C1 1000pF Piezo Sensor      SN35610
R2 10M C2 470pF Stereo Jack socket 3.5mm
R3 22k C3 6200pF Vero board
R4 220k C4 10n PP3 battery connector
R5 270k C5 47u 9V battery size PP3
R6 2M7 C6 100u 2m of 24SWG  tinned copper wire
R7 47k C7 10n flexible insulated wire for off-board
R8 2k2     Vero pins
R9 1k0     2 * 14 pin IC socket
    IC1 HEF4069UBP  case
        stereo headphones or earbuds
IC2 4024 IC3 LM386N3  


Next page: some preamplifier designs to give better sensitivity