Simple heterodyne detector

Last year I buit heterodyne detectors with the kids at school. This was a lot of fun, but like with al starters projects we were missing a proper frequency readout.

I made some frequency counter using a project I found on the internet but is was quite complex to build, so I made myself a new circuitboard so all can be mounted as SMT parts in a modern factory. Most parts are mounted already, only a switch, two control wheels, some and wires for battery, microphones and speaker need to be soldered as wel as the tiny LED display.


The TeensyBat detector is quite complex "expensive" and more for the advanced user. I hope these simple heterodyne detectors can be the starters detector. Still quite useful but much quicker to build and less money involved.

(The performance however can not be compared to the TeensyBat detector. It is easy to miss a bat because of tuning to the wrong frequency where the Teensybat simply translates all bat sounds to audible frequencies)


Below you can see the new circuit board plans.

The design is based on the Batlistener IV by Laurens Wolfden

And the counter is based on "simpelest frequency meter with avr" by Danyk


The heterodyne tuning range is about 15-85kHz but effectiveness of the ultrasonic transducers is highest near their resonant frequencies of 25 and 40kHz


Manual for simple Heterodyne detector
PDF – 290,4 KB 1 download
Manual for simple Frequency division detector
PDF – 269,7 KB 0 downloads

The FD detector is something I sell on "Marktplaats" I will add  more information soon. 


This image below, is not the final design. I made some minor adjustments to lower unwanted digital signals.


The enclosure is 103x63x26  which makes it a nice compact unit, on the new design we also have an extra ultrasonic transducer (for lower frequencies) the first ones only had 40kHz transducer and there also is a headphone connector. (The headpones connector probably is not in the most convenient place but as you can see the board gets a bit crowded.


This is the heterodyne receiver part.

This is the frequency readout.

Attiny 2313 Counter hexfile
Archive – 1,1 KB 134 downloads

How to use.

This can be a very short manual.

Place a 9V battery in the battery compartment, please be aware the lid is tiny and it is not hard to damage. The small latch needs to be at the bottom.

Turn on the detector with the slide switch in the right.

Adjust the frequency with the left tuning wheel (the frequency is shown on the display, since the actual frequency is measured there is a little lag because time that is needed to measure.

Adjust the right wheel for the volume, if the volume is too loud you can experience feedback "whisteling sounds" from the speaker.

Battery Low, there is no low battery warning, so it might be wise to bring a fresh battery with you when you head outdoors. The detector however can work on a very low battery though.

There is a trick to know if the battery is full or low. Check  the maximum frequency or your detector with a full battery. If this for example is 89kHz, it will be around 84kHz when the battery is low. (Not all detectors have the exact same range, so test  and write down your low battery frequency)



Bouwbeschrijving (building manul, dutch only for now)

Single PCB files

Bouwinstructie Heterodyne 040922
PDF – 551,7 KB 159 downloads

These Gerber bom and cpl files are for ordering a single PCB, or multiple single PCB's

If you need more PCB and want to get them populated by the manufacturer, the 6-board panels are much more effective. I used JLC PCB, the quality is reasonable and they have good price for small numbers  5-10 pcs. Please note that I did not test this actual version of the PCB, please let me know if you find something that can be made better.

Batlistner 4 gerber Singleboard
Archive – 225,0 KB 120 downloads
Batlistner 4 Schematics And Layout Images
Archive – 491,6 KB 130 downloads
Kemo G01B enclosure dimensions
PDF – 110,5 KB 131 downloads

The following files are small panels of 6 boards

The 6-panel boards allow for better build price and lager numbers, for a 5 pcs (5x6 is a total of 30 boards) the price per board is much better

Batlistner 4 gerber Panel 6pcs 3x2
Archive – 959,2 KB 104 downloads
Batlistner 4 Panel 6pcs 3x2 Bom And Cpl
Archive – 5,8 KB 104 downloads