When the Raspberry Pi Pico was announced I wanted to kick off a project to learn more about it, and the Pico announcement coincided with me starting to volunteer for Bats in Churches, a UK citizen science project. So naturally, a Raspberry Pi Pico bat detector just had to be built, and this project started to come together.

Now (July 2023) we are 2 years on, and the design has improved enormously and is in my opinion the highest-quality sub-£150 bat detector / full spectrum recorder on the market, and can be assembled for less than £20 per device when 5 or more devices are built. Here is a soundscape of bat sounds recorded for an art project by a previous-generation version of this device. Awesome or what?

When assembled the unit is a handheld, battery-powered bat detector and ultrasonic recorder, and the feature set includes a unique real-time time expansion mode, allowing you to hear bat calls live, slowed down 16x and transposed down 4 octaves, so that while out bat detecting you will hear sounds like this - not the more typical (and artificial) slapping, popping and clicking sounds generated by the heterodyne process, but the true sounds of bats, beautiful and bird-like.

An ultrasonic microphone and op amp capture and amplify broad-spectrum audio, including the ultrasonic spectrum up to and beyond 160kHz. The audio is sampled by the Pico into digital data, and is either heterodyned down or time-expanded for listening. Wav files of ultrasonic captures can be saved to SD card for subsequent offline analysis, and are saved as 384kHz / 16-bit audio. The system display is a 10 LED spectrum, driven by the Raspberry Pi Pico's hardware PWM system for silky smooth virtual analog display. Speech synthesis feedback is used for more accurate frequency detection. Three push buttons are the command inputs to the system, and an iOS app 'Pipistrelle' can be used to configure the devices. An Android app has also been developed independently, and is available as a free download fro the Google Play store.

The pipistrelle PCB is designed with a snap-off section that is used to build a frame to securely hold together the PCB and solder stencil, firmly and accurately, when applying solder paste, to ensure accurate, smudge-free stencilling.

ORDERING

When ordering PCBs, even if you only intend building 5 devices, buy 10 PCBs. The extra PCBs can be useful, and you will need at least 6 snap-off PCB sections to build the stencil frame and to use as a solder paste squeegee. Also, 5 PCBs costs $5 and yet mysteriously 10 PCBs also costs $10. So just buy 10. Bonus - there's a good possibility that PCBWay will ship you 11.

When ordering PCBs, you will need to order a stencil along with the PCBs. PLEASE do not try to make these devices without using the solder paste stencil, you will not succeed. The stencil costs a mere $10, and must be ordered as NON-FRAMEWORK. This is important - the framework stencil is not suitable for hand-application of paste.

ASSEMBLY

All the information you need to successfully assemble working pipistrelles, including device firmware images, user and assembly manual, and useful command-line tools (supplied as source code and cross-platform node.js executables) is included in the pipistrelle deliverables package, downloadable from here. As of July 2023 this zip is being constantly updated and improved, so grab from here as often as you fancy, there will always be new goodies included.

A DigiKey shopping list for parts to build 5 pipistrelles is here - if you wish to build 10 devices, change the number of assemblies from 1 to 2 - as a sanity check, the price for 5 should be £70 and change + VAT, for 10 it's around £120+VAT.

Check out the website https://www.omenie.com/pipistrelle.html for more details and any news.

If you want to get hold of me, try emailing me at phil dot atkin at omenie dot com. but be aware that I make no money at all - literally zero - from this project. It's all about the bats, and all about giving you people out there the most cost-effective bat detecting and recording equipment, at literally rock-bottom prices. So be patient if it takes me a while to answer, and please don't ask for any new features, I'm busy enough as it is.