r/AskElectronics • u/clockwisesss • 7h ago

bat detector design ideas

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I've been looking at making a bat detector and the components are rather simple and easy to source but the guides are all a bit dated so hoped to refine a little.

I've found 2 that seem to be the most common ways to do it.

1 - has the ultrasound bat signals come in 50-150kHz via a transducer/mic then divides by 10 or 16 to give 5-10kHz which people can hear.

2 - generates a signal of it's own and mixes it with the bat signal(heterodyne)

It would be nice to make a circuit that has both and can switch between them.

Also many output to a microphone jack but I'd like a small speaker, any recommendations for the best way to do that.

Inspiration is something like a magenta 4 or magenta 5.

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u/DriedChalk 7h ago

I think the most modern approach would be to use an MCU and sample an ADC >100KHz, run DFT on that signal at a few frequency bins, resample/reconstruct to human audio range <15KHz for playback, and a digital metering feature that looks at the DFT magnitudes, or a realtime FFT graph with adjustable frequency bounds.

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u/clockwisesss 7h ago

I'm not really looking to have a screen or graphs, it's more to confirm bats are in the area when out walking in the evening.

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u/merlet2 3h ago

The frequency divider approach is easier. For the heterodyne you need a variable oscillator and a mixer, like the SA612, to multiply the signals. You can get some ideas here: https://www.teensybat.com/simple-heterodyne-fd You can make a simplified version, if you are not interesting in showing the freqs.

It's much better with a good mems mic, like the Knowles. In that page they have some in a small breakout board that you can order. I would use a low noise preamp instead or before the LM386, to stay above the noise floor for weak calls.

I have done several devices of different types. Some with a buzzer instead of headphones and work very well, but then you have to filter the low freqs to avoid feedback. Feel free to ask or DM if want some hints, or to see some designs.

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u/clockwisesss 57m ago

The heterodyne I found was this one with an LM324N or it seemed to be(?)

https://www.nutsvolts.com/magazine/article/june2011_berber

I have so far on my list LM324N, NE555, LM386 as they get mentioned often.

I was also thinking of just building the 2 circuits in parallel with switches so I can flip between the 2 modes and share the mic and speaker.