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.
Once the RP2040 has clean signals, it decodes each digit, decimal point, and unit icon, then sends the reading over a low-power HC-12 link at 433 MHz to the ESP32-C3 receiver. The ESP32-C3 serves a tiny web page that faithfully rebuilds the meter's LCD in any browser on your network.
The part you would repeat for your own meter
The tedious step is mapping the matrix. Bits und Bolts probed every common (COM) and segment (SEG) line with an oscilloscope and a test jig, matching each trace to the digit or icon it lights. Do that once and the firmware knows where every reading lives. Because the same DTM0660 chip hides inside a lot of budget meters, the method ports to more than just the AN870, you just re-map the segments. Schematics, board files, and firmware are on the build page: https://www.hackster.io/news/this-modded-multimeter-streams-its-screen-straight-to-your-browser-c46d844be09b
Originally published on blog.circuit.rocks.
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