Bat Detector with adjustable gain

Bat Detector

While I stumbled upon Tony Messina’s Simple Bat Detector pages long time ago,I really decided to build one only when I saw that Bre Pettis could .

So I barely used Tony’s schematics and instructions, but spiced the circuit a bit by adding a gain adjustement potentionmeter, a on/off switch driven by the volume potentiometer, and a LED witness light.

It’s pretty easy to build : thru-hole components, some wires, …. You can use the eagle schematics included below to build yours. The latest version is single sided, and doesn’t need the flying wire on the top side like mine.

The most difficult part is to find the right compononents for the switch capable potentiometer (I choosed a push/push type : push to turn on, push again to turn off) and the box.

The push/push 10kΩ potentiometer used is a tyco Electronics 17PCSA103MC19P. You can grab it at Farnell.
The other potentionmeter is just a standard 10kΩ one, like the Tyco Electronics 23ESA103MMF50NF
The enclosure is a Boss Enclosure, model BIM RETEX 551 (Betabox Series), also available at Farnell.

What I didn’t find at Farnell is the piezo-ceramic earplug. Unfortunately, I don’t remember if I got the high (E10P) or low (S83) impedance earplug.

Grab the schematic and board here :

BatDetector Schematic

BatDetector Board

On the board, there is no connector to plug the potentiometer push/push switch. So you’ll have to wire one pin of the switch to the battery clip, and the other pin to the ‘+’ connector on the board. For ground, just wire directly.

To test your detector, if you don’t have a bat under your hand, just open a water tap and aim the detector at it : it should make lots of noise. If not, try to adjust the gain settings. If nothing works, well… something is wrong

Now, just make it and go out listen for the bats. They’re pretty easy to find in semi-urban area : bats love city lights (well, they love the insects that love the city lights), especially  mercury vapor bulbs (white lights), which attract more insects. Unfortunately, most towns are now installing high pressure sodium lamps (orange), which insects doesn’t like as much. The most common bats, Pipistrelle, emit two kind of calls :

• echolocation for hunt, around 48KHz, you’ll hear those with the detector
• social calls, around 20KHz; you can hear them without any device if you’re lucky enough (or young enough)

Finally, but you probably already know that : do not wake up hinernating bats. If you do so, they have to fly, waste energy and even if they come back to sleep again, they will get hungry too early in the season. They will have to wake up to hunt, but too early means no insects, and the bat will probably die by waking too early.

Have fun !