Heatmiser-v3-MQTT

Python Code to interact with the Heatmiser v3 Thermostats and interface with an MQTT Broker

After finding limitations on various implementations of code and home automation systems interacting with the Heatmiser v3 Thermostats, I decided to coble together my own variation and building on the work done by various folk and borrowing various pieces of code (and therefore recognition to the following is needed for the inspiration):

• Neil Trimboy
• Andy Lockran
• Flatsheep

I have finally come up with a small Python bit of code to interact with the Heatmiser v3 Thermostats using an IP to RS485 converter and to use an MQTT Broker to act as the external interface, which in my case I will be connecting up to my Openhab installation, but you could use it for any purpose really..

I will confess that I am only a hobbyist and therefore the code may not be optimal but it works for what I require.

Heatmiser Serial Interface

To connect the Heatmiser Thermostats to the network, I have used the GC-ATC-1000 TCP/IP to RS232/422/485 Converter. There are others on the market however, the more you spend the more features you get with them, preference is yours. Originally I had been using this with my Openhab set up and the Heatmiser Binding quite happily so I knew it worked, but limitations on the Openhab Binding drove me to this route. Configuration setup used on my GC-ATC-1000 is :

GC-ATC-1000

Configuration setup used on my GC-ATC-1000 is :

TCP Mode

Telnet Server/Client          	Server
Port number			1023		(anything you like really)
Remote Server IP Address	0.0.0.0		(not sure this makes a difference in normal mode)
Client mode inactive timeout	20 minute
Server mode protect timeout	2 minute

UDP Mode

  Status			Disable
  Local Port			21

UART

  Mode				RS485
  Baudrate			4800
  Character Bits		8
  Parity Type			none
  Stop Bit			1
  Hardware Flow Control		none
  Delimiter			none set

Hardware Connections

  GC-ATC-1000			Heatmiser Wiring Centre
  Pin 1 - RS485 +		Touchpad 'Y'
  Pin 2 - RS485 -		Touchpad 'B'
  Pin 3 - Not used		-
  Pin 4 - Not used		-
  Pin 5 - Vin			-
  Pin 6 - GND			-

Raspberry Pi

For the actual running of the scripts I have just used a Raspberry PI Model B. It does not have to be that powerful for this lot. As it happens I have been using one for monitoring my boiler, so it was just as easy to use that.

In theory when running the scripts and assuming that you have set the right IP addresses and port numbers, then this should just all fire up and off you go. However, I did have quite a few teething problems when starting off. Trial and error with a lot of this and a good dose of WireShark.

MQTT Broker

For my installation I have used the Moquitto MQTT Broker installed on a second Raspberry Pi which sits on the Openhab server. Again it should not really matter what broker you want to use. If you go for a hosted MQTT Broker then you will probably have to modify the MQTT Broker connect functions in 'heatmiser.py' and 'mqtt.py'

The Code Blocks

There are four main code blocks:

constants.py

Used to store all the static global variables used by all the various utilities

mqtt.py

This utility quite simply monitors the MQTT Broker for those topics which are required, as defined within the thermostat array from 'constants.py' and places any updates received into a queue for processing within 'heatmiser.py'. As the interface with the Thermostats was only ever desiged as a serial process interface with a single master, I needed to use a single script to control the comms with the thermostats

logger.py

Just really used to log any messages generated from 'heatmiser.py' and 'MQTT.py'.

heatmiser.py

This is the main engine of the whole thing. However to simplify this a bit:

• The script polls the thermostats on a regular basis and posts any updates needed to the MQTT Broker
• Only changes are sent to the MQTT Broker not all updates from each poll cycle
• Inbetween each poll the script sees if there is anything to process from the MQTT Broker and processes 1 message every poll cycle
• Every hour the script updates everything to the MQTT Broker, just in-case
• Every day at 03:00, the script updates the time of every Thermostat

That's it..

Installation

Mostly the installation is easy, just place the python files in a directory you want to run this from, update the constants file with your own local settings and off you go. However, you will need the following to run:

Paho MQTT Client

• pip install paho-mqtt

Future Plans

For the future I plan to create a web interface to this utility such that I can interact a bit more with the Thermostats, especially for functions like controlling centrally the On/Off timers, where a home automation system may not be that ideal for this and gives you the ability to run the heating off-line.

Also I intend to integrate the boiler monitoring scripts such that I can better control and monitor this. My specific set-up is a Biomass Boiler, so needs a little more TLC than just a bog standard wall-hung gas or oil boiler.