An ESP32-C3 turns a 3D-printed wheel into a fishing line meter

Difficulty

Intermediate

AI-buildability

4/5

The firmware (pulse counting, OLED display, calibration) is easy for AI tools to write, while the soldering, magnet placement and 3D-printed enclosure still need hands-on work.

Time

A weekend

Cost

$10–25

Estimates based on the original write-up. How AI-buildability is scored. Building with an AI assistant? Connect it to Afterware (free MCP server).

Wrap fishing line once around the side wheel and pull. The wheel spins past six magnets, an A3144E Hall sensor catches each pass, and an ESP32-C3 SuperMini counts the falling edges. Multiply the pulse count by a calibrated distance per pulse and a 0.96-inch OLED shows meters in big digits, with two decimal places.

The build runs on parts most benchmarks already have: the C3, a Hall module, a small SSD1306 screen, magnets and a 3D printer. There's no custom PCB and no pinch roller. The Hall output needs care, though. On this prototype the S line sat at 3.73V with no magnet, so the write-up adds a resistor from S to GND and recommends a BSS138 level shifter if you can't characterize your module.

Worth stealing: the wheel-and-magnet trick is a cheap way to count any rotating thing, and the calibration math (pi times 28mm divided by six) is spelled out so you can redo it for your own line and wheel.