I just installed a Daikin split system (AC/Heat Pump) and would like to control it remotely. There are similar units available which can be controlled with an IR remote, but mine does not support this option. The only way to control it is to use their thermostat device which uses an unknown protocol to send commands to the indoor and outdoor units.
Here are the model numbers for the components in the system:
Indoor Unit - FCQ18PAVJU
Outdoor Unit - RZQ18PVJU9
Remote Control - BRC1E72
The remote controller is powered and transmits data over the two wire cable that connects it to the indoor unit.
The system supports a second controller as a slave, so the ultimate goal is to create a circuit to act as the secondary controller which will interface with a home automation system.
I have sampled the signal with an oscilloscope to see what's going on, but I'm not sure how to proceed with decoding the format.
The signal has a DC offset which is mirrored by the voltage on the other wire. The sum of the voltages on the two wires is always exactly zero. On the small scale, it is sinusoidal. There are regular fluctuations in amplitude, but I'm not seeing a bit pattern. Maybe it is frequency encoded.
See the full 2.4 second capture here in .csv format: