Tuesday, 4 August 2015

Bat Detector Overhaul: Portable Field Unit

Sooner or later I'm going to have to accept that the bats are not coming to me, so I need to get out and find them!

I could do that now just using the hand-held bat detector. But I'm thinking it would be nice to test the whole automatic design illustrated in an earlier post.

So I've put together a rough outline schematic and started collecting bits & pieces.

There is very little here that I've not already done before.

The 2 box portable bat detector

By having a two box design, linked together via a (say) 2m screened cable, I can wave the small detector around in the air while either putting the main box on the ground or safe inside a jacket pocket. A 3 pole, 3.5mm jack would connect 9V, signal and common (0V) between the two boxes.

If I could get 2-3hr operation out of 6 rechargeable AAA batteries that would be plenty. Otherwise I'd have to use the slightly bulkier AA variety.

The Picaxe power controller is a re-hash of my birdbox design. Except that a push button would cause the Picaxe to power the Pi, blocking all further button operations for (say) 2 minutes. Pushing the button again after 2 minutes would instruct the Picaxe to notify the Pi to shutdown, with power removed from the Pi after a further 30 seconds.

The battery voltage needs to be greater than 6.5V for the 78B5.0 voltage regulator to provide a stable 5V to the Pi. So the Picaxe can monitor the voltage and shutdown the system if the voltage drops below 7Volts, keeping the system off until fresh batteries were fitted.

For headphone only operation, I probably would not need an audio amplifier. The second push-button would allow the last/most recent recordings to be played back (through headphones or speaker). This would give me something to do while waiting for the next fly-pass.

The time problem

If the time of recordings was important, a real-time clock would be necessary. However, it may be enough just to note the time that the unit was switched on and mentally apply a time offset when interpreting system time-stamps.

The other time problem is that I don't have any spare at the moment (come on! It's summer) so I can't see this project getting much attention this side of Guy Fawkes night.


  1. Detecting bats will be tricky alongside fireworks... I remember vaguely thinking about doing something like this a while ago, but that's as far as I got... Nice to see that others have similar ideas :)

  2. Hey, what about a Mobile Bat Detector?

    I was thinking of clamping a detector to the roof bars of our Ford Fusion!