I built a bat detector some time ago but never really got a chance to try as the bats seem to have left.
Fetching the detector from the workshop, I pointed it at the trees, switched on and waited… and waited… and waited… eventually some quick audio bursts were heard and we saw the culprit fly past; doing some rather impressive aerial manoeuvres as it happens whilst catching his dinner.
So, I know the detector works, but the next job is to increase its sensitivity – that’s this weekend’s project.
Once it’s done, I’ll post up the circuit here.
*Update*
The weekend came... the weekend went... as did the summer.
Looks like I'll have to try this again next year.