MAX30102 $3 Heart Rate Monitor One of those AliExpress impulse buys finally earned its keep: I paired an ESP32-C3 with a MAX30102 and a tiny OLED to build a pocket pulse oximeter. A bit of I2C wiring, a ring-buffered sampler, and the MAX30102 HR/SpO2 algorithm later, the onboard LED is thumping along with my heartbeat and the readings match a commercial unit (~70 BPM, 99% SpO2). It’s a little finicky about finger placement, but for a few bucks it works brilliantly. 15 March 2026