When the first batch of Lu.i PCBs was delivered in Juli 2022, we were funnily enough spread across the globe and could thus get together only virtually. The PCBs arrived almost fully populated, just the coin cell holder had to be soldered manually.

We had gone all in: Time constraints did not allow for an initial smaller prototype batch, and we had ordered a total of 100 little neurons! Our pre-fabrication verification was thus limited to SPICE simulations. Our limited confidence in those was further reduced by the fact that – with the design being powered by a coin cell – we could only barely honor the specified voltage limits of the used components.

We were super excited when the LEDs immediately lit up – but the circuit appeared somehow broken and reacted unpredictably to us turning the little potentiometers. After some tinkering, we found the first (and only "significant") bug: We had messed up the silkscreen! The markings for the two potentiometers for the membrane timeconstant and the leak potential were swapped🤦 Nothing that we could not fix with a few stickers. One hundred stickers. Well, could have been worse!