A Solenoid and an Amplifier Allow This Raspberry Pi to Sing You a Song While It Works
By picking up electromagnetic interference with the solenoid and amplifying it into audio signals, you too can hear your machine think.
Pseudonymous maker "The Sink God," hereafter simply "Sink," decided to look at what a Raspberry Pi single-board computer was doing in a different way — by capturing electromagnetic interference in a solenoid and turning it to audio.
"I made a simple circuit that allows me to listen to the electromagnetic interference produced by all kinds of electronics," Sink explains of the project, "and in this case thought it would be interesting to use a Raspberry Pi with the device 'listening' to the board."
That simple circuit: a solenoid connected to a Texas Instruments LM386 low-voltage audio power amplifier. As the circuits of the Raspberry Pi do their work, they create electromagnetic interference in the solenoid — interference, which is amplified by the LM386 in order to produce audible sounds.
"I placed the solenoid on top of the board, as close as I could with only a small layer of plastic in between to prevent the solenoid's metal housing from shorting anything out on the Pi," Sink explains. "The output of the LM386 (+ ground) are hooked up to my laptop's microphone jack."
Exactly what you hear depends on what the Raspberry Pi is doing: Sink ran a series of workloads, from simply logging in and running the htop system monitor to the bandwidth-heavy process of downloading software updates via apt and even stressing the CPU with the SysBench benchmark tool.
"Something I want to do at some point is add an adjustable frequency divider and band-pass filter to the circuit," Sink adds, "so I have greater control over the audio output. Might help hone in on specific sounds/components.
Sink's full video is available on YouTube.
