Simen E. Sørensen Brings That Record-Scratch Moment to Your Favorite Badge — with an RP2040
"This SAO is kind of ridiculous," its creator admits — "closer to a badge than it has to any other SAO I've ever designed."
Maker Simen E. Sørensen is bringing the classic record-scratch moment to a new medium: the Simple-Add On, with a Raspberry Pi RP2040-powered SAO bringing an interactive version of the familiar "wicka-wicka" sound to any compatible electronic badge.
"This SAO is kind of ridiculous," Sørensen writes. "I'll be the first to admit that the feature list […] grew a bit out of hand. The SAO has ended up closer to a badge than it has to any other SAO I've ever designed. But in my opinion 'the SAO' (as a concept) is at its strongest when you can give it away to someone, they can plug it in, and it will start doing its thing."
"Its thing," in this instance, is playing the classic "record scratch" sound — not in response to a button press, but in response to the user's motion across four capacitive touch-sensitive pads arranged around a PCB shaped like a miniature vinyl record. Despite its diminutive size, the add-on includes both a Raspberry Pi RP2040 microcontroller and 4MB of external flash, an Analog Devices MAX98357A I2S amplifier connected to a "teeny-weeny speaker," an addressable RGB LED, a physical on-off switch, a USB Type-C port, and a debug header.
On the firmware front, Sørensen ran into a few problems with reversing audio playback — and, facing a deadline to get the device ready, decided the quickest fix was to create a custom fork of CircuitPython. "The result is honestly really bad," Sørensen warns, "but it works, and since adjusting the playback direction of a Note doesn't really make a lot of sense in the upstream version of CircuitPython, I'll just keep my broken code in a fork that does nothing other than this one specific modification."
Sørensen has documented the build on Hackaday.io, with more information in this Mastodon thread.