Can I buy a pre-assembled device?
Unfortunately you can't buy a device assembled. I have not yet found a manufacturer who meets my rather inflexible criteria - lowest consumer price possible, and taking over all software support - so until the right manufacturer appears you will need to either make one yourself, or club together with bat / electronics enthusiasts to collaborate and build a number of them. There have already been many "Build your own bat detector" workshops around the world, typically in Maker Spaces, so contact your local Maker Space and see if it would be of interest to them.
Can I download the schematics / Gerbers and make my own PCBs? I'd rather not use PCBWay.
Once the schematics or Gerbers leave my hands there is nothing to stop unscrupulous people from manufacturing these, making a lot of money and offering no support at all, leaving me in an unsustainable situation with a massive support burden. So no, you can't, just order the number you need from PCBWay, it's extremely cost-effective and their PCBs are consistently good quality.
Can I download the source code? Is it an open source project?
See "Can I download the Gerbers ..." - no and no, for the same reasons.
Can I use pippyg for non-ultrasound projects? Can I reduce the sample rate and use it to capture birds?
Right now, no / maybe. This may change in the future, but the sample rate in particular will be difficult to change, there are assumptions about the sample rate and about the devices being ultrasonic buried deep in the code. So for now, the sample rate will stay at 384kHz, and I will see what I can do to modify the software that triggers recordings to enable "trigger on non-ultrasound".
I'm not in the UK and would like to change the set of species frequencies for manual heterodyning - is that possible?
Yes, the "interesting frequencies" can be changed by modifying the configuration string and reflashing your devices - look at the software tools section of the deliverables zip file for more details on how to do this.
Is it normal for pipistrelle to enter heterodyne mode when I trigger a recording?
It is. The available memory on the Raspberry Pi Pico is small, and there simply isn't enough to allow simultaneous recording and time expansion, so the device must enter heterodyne mode when recording. Similarly, the device must be in heterodyne mode when the pipistrelle chirp app is used to configure the real-time clock.
Can I use a FAT formatted SD card?
Can I use <enter name here> SD card?
Can I use <enter size here> SD card rather than 32GB?
No, your cards must be formatted ExFAT. I can't test them all, so try your own card and see. I recommend SandDisk Extreme 32GB, they are the best I have tested.
Can I use a hot air gun rather than a hotplate to make these devices?
Honestly, I don't see why not - I don't have a hot air gun so have never tried it, so feel free to try.
My pipistrelle can't see the SD card - it was fine yesterday but now it flashes green and fast on power-up.
Check your batteries. The SD circuit is powered by an LDO which will fail at a higher voltage than the Pico - so if your batteries are down to under 2.8V or so, the Pico and the analog circuitry will be fine, but the SD card interface won't work. So first port of call, try fresh batteries.