MitsubishiSC

Smart controller for Mitsubishi Electric HVAC systems.

Usage

The platformio.ini defines the list of build environments. Each board configuration comes in debug and release builds.

Build

To compile the firmware, use the pio run command with the designated build environment.

pio run --environment mitsubishisc_v1_release

Flash

To flash the build artifact to the board, connect the board and run the pio run command with the upload target.

pio run --target upload --environment mitsubishisc_v1_release

Concepts

Protocol

The CN105 connector exposes the UART interface via the RX and TX pins. As discovered by Hadley Rich, this uses 5V TTL 2400 8-E-1.

Since the ESP32/STM32 runs on 3.3V while the UART runs on 5V, there is a need to use a logic level shifter. BSS138 is a N-channel MOSFET with a low $V_{GS(th)}$, which makes it more ideal than other NMOS components.

For more information about the packets, refer to mUART Protocol Reference.

Hardware

MCU

As part of the project goals, we want to build a device that leverages on the Matter standard for maximum compatibility and Thread for low-power, low-latency performance. The selected microcontroller should have the following features:

• Support for WiFi and Thread
• Support for Matter over WiFi/Thread

Manufacturer	MPN	Type	Price
Espressif Systems	ESP32-C6FH4	SoC
Espressif Systems	ESP32-C6-MINI-1	SoC
STMicroelectronics	STM32WB55CGU6	SoC	US$3.48
STMicroelectronics	STM32WB5MMG	SoC
Nordic Semiconductor	NRF52840-QIAA-R	SoC	US$3.41

NOTE: The SKUs from LCSC Popular Products are preferred to ensure good price and supply.

Connector

The Mitsubishi Electric air conditioner has a CN105 port that appears to be a JST PA connector. To fit this, we should use PAP-05V-S housing with SPHD-001T-P0.5/SPHD-002T-P0.5 contacts.

DigiKey stocks the APALPA22K305/APAPA22K305 pre-crimped cables in 22 AWG, 12" cables.

According to the LCSC team, the HCTL HC-PA-5Y and HC-PA-T are equivalent replacements for this part.

Power Supply

The STM32/ESP32 runs on 3.3V but the CN105 connector only exposes 12V and 5V power rails.

To power the MCU, we use a low-dropout linear regulator to regulate 5V to 3.3V. MCP1700 is chosen for its low quiescent current ($I_Q$) but any modern LDO should work.

License

MIT