Introduction

This is a small ESP8266 and ESP32 compatible program to make your Mitsubishi HVAC speak Modbus.

For additional resources, consult the following resources

• https://nicegear.nz/blog/hacking-a-mitsubishi-heat-pump-air-conditioner/
• https://github.com/SwiCago/HeatPump/
• https://github.com/rjdekker/MHI2MQTT/blob/master/README.md

I'm personally using dev version of ESP8266, which can power using 5V directly. No issues so far.

For dummies, this the connection:

• HVAC DC 12V (unconnected)
• HVAC DC 5V <-> ESP 5V
• HVAC GND <-> ESP GND
• HVAC TX <-> ESP RX
• HVAC RX <-> ESP TX

The CN105 cable I bought from usastore.revolectrix.com.

Getting started

1. Rename secrets.h.example to secrets.h. Replace with Wifi credentials
2. Check constants.h and modify settings accordingly
3. Upload SPIFFS / File System Image
4. Upload code

Remote upload works as well, uncomment relevant lines in platformio.ini.

Operation

The programs kicks off a Modbus TCP server. In addition, it acts as Modbus client, writing the data to predefined Modbus server every ~1s. In my experience, at least with ESP 8266 the Modbus client is more reliable method of integration. You can enable/disable Modbus features in constants.h. Currently client is necessary to control the heatpump via Modbus.

The ON/OFF command is read from the remote Modbus server, and heatpump is commanded accordingly.

Please find the definition of Modbus data in main.cpp comments.

The ESP logs its operatoin via UDP. You can use wireshark or tcpdump to listen for the data. Example: tcpdump -nnASs 1514 src 192.168.1.167 and port 514

The program also opens up a simple web server for controlling the heatpump. With ESP8266 this is quite unreliable in practice.