Introduction
This article is a follow-up of my previous (old) French post “Domotiser une ancienne chaudière mazout : Gestion du thermostat“. That previous built used a custom firmware to control relays, measure water temps and show status on a OLED screen.
Time has past and Tasmota is a very capable and easy to integrate framework. I don’t use much the OLED screen so I decided it was time to get rid of that old custom software.
Obviously, Tasmota supports OLED displays, I might consider going down the docs at Tasmota > Features > Displays. A custom build using USE_DISPLAY_SSD1306 will be required as well as quite some read.
Hardware
This built is similar to Monitoring a boiler using Tasmota on ESP8266 and DS18B20 sensors but adds relays to control the Power and Circulator.
Another option is to use an OpenTherm interface but that’d require changing my physical thermostat. As far as possible I prefer non invasive hacks that are easy to reverse.
The below overview shows the main components such that:
- WeMos D1 Mini ESP8266 is used as the main controller
- 5V relay module is used to control power and circulator (heating)
- DS18B20 are used to measure outgoing and returning water temperatures
- Optional : I2C OLED 0.96 inch display module from my initial build using Homie. This post does not cover its use with Tasmota.
- Optional : DIN Power Supply (5V, 15W) to power the build
- The Zigbee network controlling the radiators valves, this is out of scope for this post:
- Sonoff ZBDongle-P as Zigbee gateway
- Zigbee radiator valves from MOES at each radiator
Overview
Wiring temperature sensors
Wiring relays
Test bed and wall box assembly
Breadboard
Protoboard wiring Front
Protoboard wiring Back
Breadboard and assembly
Test bed on desk
Test bed in wall mount box
Bill Of Materials
The BoM is exactly the same as for the Monitoring a boiler using Tasmota on ESP8266 and DS18B20 sensors except you need one or two relays to control the furnace power / circultor.
| Part | Quantity | Approx. Price |
| Perfboard : Main PCB to put your assembly | 1 | 15€ for a set of 34 |
| PCB 2 pin terminal : Optional direct 5V power input | 1 | 10€ for a set of 50 |
| PCB 3 pin terminal : One per temp sensor | 4 | 14€ for a set of 50 |
| WeMos D1 Mini ESP8266 : The brain | 1 | 5€ |
| DS18B20 : Waterproof temp sensors with 1m wire | 3 | 10€ for a set of 10 |
| Flexible silicone wire rolls : To wire the board | 1 | 12€ for a set of 5 spools of 10 meters |
| Resistors assortment kit : One 4.7Kohm for data bus of DS18B20 | 1 | 5€ for a set of 500 |
| 5V relay module : Use a 2 Way to control power and circulator, 1 Way for circulator alone | 1 | 2€ |
Software
Tasmota
Just connect your WeMos D1 Mini ESP8266 to your computer over USB and install the regular Tasmota image using https://tasmota.github.io/install/.
To configure your board, use Module type = Generic(18) with below settings (adjust based on your actual wiring):
- D5 GPIO14 : Relay_i #1 for Power
- D6 GPIO12 : Relay_i #2 for Circulator
- D7 GPIO13 : DS18x20 #1 – As the DS18B20 uses a bus, a single data pin is required for both sensors (or more!)
Finally configure the MQTT to point to you Home Assistant server.
Home Assistant
In HA, make sure to setup the Tasmota integration, this will detect your Tasmota device over MQTT and setup the entities automatically.
Once entities are present in HA, I included them as shown below.
Here is the YAML configuration
type: vertical-stack
cards:
- cards:
- show_name: true
show_icon: true
entity: switch.tasmota_furnace_relay_power
hold_action:
action: none
tap_action:
action: toggle
type: button
icon: mdi:power
- show_name: true
show_icon: true
entity: switch.tasmota_furnace_relay_circulator
hold_action:
action: none
tap_action:
action: toggle
type: button
icon: mdi:engine
type: horizontal-stack
- type: history-graph
entities:
- entity: switch.tasmota_furnace_relay_circulator
- entity: sensor.tasmota_furnace_ds18b20_1_temperature
- entity: sensor.tasmota_furnace_ds18b20_2_temperature
hours_to_show: 8
refresh_interval: 1
title: Chaudière
Creating a thermostat based on Node-RED
My initial logic was to write a loop and accordingly act within the loop.
This proved to be a big PITA as multiple messages started flowing down the pipe, causing havoc. Concurrent messages interfered with the control logic and the switch was kind of flashing.
I’m now using a much more simple approach : Allow a single message at any given time, killing any undesired control message while already busy. This looks like a critical section and is achieved using a semaphore. The semaphore is a simple flag set early and released when job is done (or skipped).
Here is pseudo code code for this control logic:
- Triggers :
- Every minute (heat/rest are whole minute based) for full automation
- Manual trigger from Node-RED
- When mode is changed from UI
- Check if allowed to send a command using a semaphore gate (“Is it already busy?”)
- Get defined settings (heat/rest durations and auto/manual control)
- Based on thermostat mode
- Manual : Stop automation here for obvious reasons
- Automatic : Run automation with settings defined in UI
- Otherwise : Build message with predefined settings, based on heating strategy
- Run heat/rest magic
- Update UI using new settings (heat/rest durations)
- Heat for specified duration (turn on circulator) and wait
- Rest for specified duration (turn off circulator) and wait
- Clear the semaphore to allow further messages (“I’m done, ready to work”)
Here is the actual flow along with its JSON:
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thermostat mode\nconst heatingModes = new Map([\n [cThermostatModeManuel, { heat: 0, rest: 0, boiler_mode: cBoilerModeManual }],\n [cThermostatModeAutomatique, { heat: 0, rest: 0, boiler_mode: cBoilerModeAuto }],\n [cThermostatModeNormal, { heat: 2, rest: 10, boiler_mode: cBoilerModeAuto }],\n [cThermostatModeBoost, { heat: 10, rest: 1, boiler_mode: cBoilerModeAuto }]\n]);\n\n// Based on Thermostat mode, get active settings\nconst settings = heatingModes.get(thermostatMode);\nmsg.thermostatMode = thermostatMode;\nmsg.duration_heat = settings.heat;\nmsg.duration_rest = settings.rest;\nmsg.boiler_mode = settings.boiler_mode;\n\n// If manual : Clear semaphore and drop message\nif (cBoilerModeManual == msg.boiler_mode) {\n //node.warn(\"Thermostate mode - manual mode, skipping\");\n global.set(\"furnaceControlBusy\", undefined);\n return;\n}\n\n// Overwrite if \"Automatique\" (aka automatic with values from UI)\nif (cThermostatModeAutomatique == thermostatMode) {\n if 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UI"},{"id":"c5cb1b119f3345f7","type":"delay","z":"8fcdcb3d.6fcf08","name":"Heating","pauseType":"delayv","timeout":"3","timeoutUnits":"minutes","rate":"1","nbRateUnits":"1","rateUnits":"second","randomFirst":"1","randomLast":"5","randomUnits":"seconds","drop":false,"allowrate":false,"outputs":1,"x":1240,"y":560,"wires":[["aae85b34d38269a4"]]},{"id":"4d3783b50a776937","type":"delay","z":"8fcdcb3d.6fcf08","name":"Rest","pauseType":"delayv","timeout":"7","timeoutUnits":"minutes","rate":"1","nbRateUnits":"1","rateUnits":"second","randomFirst":"1","randomLast":"5","randomUnits":"seconds","drop":false,"allowrate":false,"outputs":1,"x":1230,"y":620,"wires":[["7ebe38ac487147ad"]]},{"id":"f4fafa0d3b3007c0","type":"api-call-service","z":"8fcdcb3d.6fcf08","name":"Heat","server":"1e5e7dca.395042","version":7,"debugenabled":false,"action":"switch.turn_on","floorId":[],"areaId":[],"deviceId":[],"entityId":["switch.tasmota_furnace_relay_circulator"],"labelId":[],"data":"","dataType":"json","mergeContext":"","mustacheAltTags":false,"outputProperties":[],"queue":"none","blockInputOverrides":false,"domain":"switch","service":"turn_on","x":850,"y":560,"wires":[["47b10d30590d174c"]]},{"id":"aae85b34d38269a4","type":"api-call-service","z":"8fcdcb3d.6fcf08","name":"Rest","server":"1e5e7dca.395042","version":7,"debugenabled":false,"action":"switch.turn_off","floorId":[],"areaId":[],"deviceId":[],"entityId":["switch.tasmota_furnace_relay_circulator"],"labelId":[],"data":"","dataType":"json","mergeContext":"","mustacheAltTags":false,"outputProperties":[],"queue":"none","blockInputOverrides":false,"domain":"switch","service":"turn_off","x":850,"y":620,"wires":[["00e64e5136b06f41"]]},{"id":"47b10d30590d174c","type":"function","z":"8fcdcb3d.6fcf08","name":"Set delay","func":"const globalHomeAssistant = global.get('homeassistant').homeAssistant;\n\n// Get delay from slider\nvar delay = 2; // Default\nif (globalHomeAssistant.isConnected) {\n delay = globalHomeAssistant.states[\"input_number.slider_boiler_heat\"].state;\n}\n\n// Update message\nmsg.delay = Number(delay) * 1000 * 60; // Cast delay to milliseconds\nreturn msg;\n","outputs":1,"timeout":"","noerr":0,"initialize":"","finalize":"","libs":[],"x":1080,"y":560,"wires":[["c5cb1b119f3345f7"]]},{"id":"00e64e5136b06f41","type":"function","z":"8fcdcb3d.6fcf08","name":"Set delay","func":"// Constants\nconst globalHomeAssistant = global.get('homeassistant').homeAssistant;\nconst cMinDelayEco = 10;\n\n// Get delay from slider\nvar delay = 0; // Default\nif (globalHomeAssistant.isConnected) {\n delay = globalHomeAssistant.states[\"input_number.slider_boiler_rest\"].state;\n}\n\n// Check if \"Chauffage éco\" is enabled, limiting max temp for all rooms\nif (\"on\" == globalHomeAssistant.states[\"input_boolean.chauffage_eco\"].state) {\n if (delay < cMinDelayEco) {\n delay = cMinDelayEco;\n }\n}\n/*\n*/\n\n// Update message\nmsg.delay = Number(delay) * 1000 * 60; // Cast delay to milliseconds\nreturn msg;\n","outputs":1,"timeout":"","noerr":0,"initialize":"","finalize":"","libs":[],"x":1080,"y":620,"wires":[["4d3783b50a776937"]]},{"id":"64e5573c0732e7ce","type":"inject","z":"8fcdcb3d.6fcf08","name":"Start thermostat","props":[{"p":"payload"}],"repeat":"","crontab":"","once":false,"onceDelay":"10","topic":"","payload":"","payloadType":"date","x":800,"y":140,"wires":[["baf53ed4484f08a4"]]},{"id":"11c89048274bdefe","type":"api-call-service","z":"8fcdcb3d.6fcf08","name":"Set 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Conclusion
I enjoyed working on this build and it is probably the hardware I use the most for my home automation. The use of Tasmota dramatically simplifies its deployment and maintenance.
However this is only one of three big parts for my heating automation:
- Furnace control : This post
- Radiators control using Zigbee valves : It’s as simple as adding the Sonoff ZBDongle-P and some Zigbee radiator valves from MOES
- Full radiators automation : Home Assistant to control per room valves on a schedule
I still have some work to put on automating the heating itself. I’m currently relying on the physical thermostat and manual circulator control.
