How has this Daikin control signal been encoded?

Question

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.

Partial Zoom (One Wire)

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:

Answer 1

As Marko answered, it is the Daikin proprietary P1P2 protocol. At the lowest level it is a 9600 Baud serial-like interface based on the Japanese Home Bus System (HBS, ET-2101). Technical details of this standard can be found in chapter 4 of the Echonet specification. HBS uses a variation of bipolar encoding (alternate mark inversion, https://en.wikipedia.org/wiki/Bipolar_encoding), but the pulses only take half of the bit time. So every falling edge in the signal represents a 0, and every "missing" falling edge represents a 1. Every byte is coded as a start bit (0), 8 data bits (LSB first), 1 parity bit (even), and 1 stop bit (1). Oscilloscope pictures which show the signal are made by another user and published on http://www.grix.it/forum/forum_thread.php?ftpage=1&id_forum=1&id_thread=519140&tbackto=/forum/forum_discussioni.php?id_forum=1. As it is a two-wire interface, devices should not write on the bus if any other device is writing. The HBS standard has an advanced collision detection and priority mechanism. Daikin does not follow the HBS packet format or HBS timing specification. In a 2-device set up of a Daikin heat pump and a thermostat, the devices seem to simply alternate turns in writing to the bus.

A power feed for the thermostat is also added to this signal: the average potential difference between the two wires is 15V DC.

More documentation and how to read and decode the data yourself is available on github: P1P2Serial.

Answer 2

The best you can do is to teardown the remote controller and post picture. The remote will certainly have a standard transceiver chip, like PLC, LON, CAN ...some protocol for building automation.

Probably is coupled/decoupled by some transformer or capacitors, since only two wires are for power supply + communication.

Little googling: it is Daikin Proprietary P1P2 protocol.