A Raspberry Pi Pico based bat echolocation synthesizer.

NOTE - the PCB and 3D print files were updated on the 4th June 2025. Connections for +5, +3.3 and a pair of GPIOs have been brought out to solderable pads, so that external circuitry can trigger bat calls.

Here's the DigiKey shopping list : https://www.digikey.co.uk/en/mylists/list/4NDKM2PQQG

In addition to this shopping list, each Bat Synth requires an LTK5128 Power Amp module, which is surface-mounted to the Bat Synth PCB. The module can be found on Amazon UK here, and eBay as well - https://www.amazon.co.uk/DollaTek-Class-Digital-Amplifier-Board/dp/B09CGW3M4F/ref=sr_1_19 - but do shop around for these, they can be found VERY cheaply on eBay (e.g here : https://www.ebay.co.uk/itm/356670287815) and literally pennies on AliExpress.

Firmware with 8 UK bat species : https://drive.google.com/file/d/1d3VLmw3UvsXdXn6b2KHH74an4kNRdKfs/view?usp=share_link Note that I am working on a system to allow users to program their own bat calls and bat passes, but it’s not ready yet. Watch this space for updates.

NOTE that you MUST provide adequate power over USB. The circuit demands over 1A, and to avoid audio distortion the USB 5V supply must be stable and not droop at this current level. A USB-C to micro USB cable is best and will result in highest quality audio. The circuit contains bleed resistors to allow USB power banks to be used without keep-alive circuits, which have been seen to adversely affect audio quality and current delivery. If you only use a quality wall supply you could omit these (the 4 resistors to the right of the Pico, under the speaker).

The device really needs to be weighed down to be mechanically stable. What works well is to jam 3 pennies (UK pennies) into the 3D print case. The top coin is tight against the 3D print, and friction keeps the pile of 3 coins in place, and results in a stable setup. To make sure they don't fall out I hot glue mine in place with tiny blobs of glue.

UNDER NO CIRCUMSTANCES MAY ANY DEVICES BUILT BE EITHER RESOLD, OR OFFERED FOR SALE.

THIS PROJECT IS SUPPLIED ON A STRICTLY NON-COMMERCIAL BASIS. I MAKE NO MONEY FROM THIS PROJECT, AND IN RETURN, BY BUYING PCBS HERE, YOU COMMIT TO MAKE NO MONEY FROM THIS PROJECT.

BE NICE, OK?