I’m trying to build a power use monitor, reading infrared pulses emitted by my electricity meter using a phototransistor. I have a working circuit with phototransistor and pull-up resistor that is working well when I test it on breadboard and soldered to experimental board with a short (~1m) cable.
However, my electricity meter is located in a cabinet outside, so I’ve run a cable (unshielded 4x0.2mm, using three of the wires) which is about 10 meters long, and in this setup, I seem to get an unstable signal, with the digital input flickering between HIGH and LOW very quickly. If I send infrared pulses to the phototransistor I can see that they get through, but with so much noise that it’s impossible to use.
Being a bit new to electronics, I imagine I’ve hit some kind of standard problem transferring signals over long cables, so I’m looking for an explanation of what’s happening, and ideas on how to solve the problem?
The phototransistor (LTR3208E) and its pull-up resistor (1MOhm) is at the electricity meter end of the cable, but I’ve also tried having the pull-up at the arduino end with the same result.