As I mentioned a few days ago, I am trying to build an ultrasonic “bat detector”, with the aim of using a Raspberry Pi to record and transpose the inaudible noises given off by bats as they fly around the night sky. I researched the different types of microphones and eventually ordered a pair of Panasonic WM62A electrets.

They arrived yesterday, and caused me some confusion. I picked up a padded bag and saw who it was from, so I excitedly opened it. I yanked out the folded paper invoice and reached into the bag, to find … nothing. I even looked inside just to make sure. There were no microphones there. Surely the supplier would not send just the invoice in a padded bag? When I unfolded the invoice, there, nestled in the creases was a small silvery plastic pack, about the size of those silica gel packs you often find, or perhaps the size of the little packs of screws you get with a new hard drive. Inside it were the two tiniest microphones I have ever seen. Just 6mm in diameter. Some microphones really are “micro”!

Now, though, I have to work out how to solder some wires to them, and what kind of circuit I might need to get the output signal into some sort of shape for feeding in to my raspberry Pi.

It’s not just microphones that are getting smaller, either. The Freescale KL02 is a complete ARM 32-bit “system on a chip” with 32K flash, 4K RAM, analog and digital IO, which measures about 2mm square. Yikes!