Want live multimeter readings on screen during a build video without fighting glare, focus hunt, and awkward camera angles? You can, and the parts list is short: an ANENG AN870 meter (any clone built on the DTM0660 chip works), an RP2040 board to sit inside it, a pair of 433 MHz HC-12 radios, an ESP32-C3 to host the page, and one small comparator board you will make yourself.
YouTuber Bits und Bolts got tired of those filming headaches and built AirMeter, an open-source mod that taps the meter's own LCD signals and redraws the display live in a web browser or as an OBS source. No proprietary app, no cloud account, no soldering to a hidden data port that may not even exist.
Reading a screen that does not want to be read
That last point is where the project gets clever. The AN870 has a hidden UART, but the manufacturer left the processor pin it needs disconnected under a blob of epoxy, so serial access was a dead end. Instead, the RP2040 samples the signals that drive the LCD directly. That display is a 4x15 multiplexed matrix: 60 individual segments controlled through only 19 physical traces. Those lines do not carry clean digital logic, they carry four-level analog waveforms, so a custom board populated with five LM339 comparators squares them into levels a microcontroller can actually read.
