Heater Flow

As promised, I am going to present the flow used for the thermostat node. This flow has a nice dashboard, so it can be controlled from my phone, or from the thermostat, or any other flow input.

The flow:

We can start from the center, the "Check Thermostat" function node. This function take inputs from the heater/state, sunroom/thermostat and sunroom/temperature MQTT topics. The heater/state is published by the nodeMCU attached to the heater, and the payload is either "on" or "off" depending on the state of the heater. The sunroom/thermostat and sunroom/temperature topics are from the thermostat nodeMCU from the last post. The sunroom/temperature payload is a number indicating the temperature measured by the DHT-22 sensor converted to degrees Fahrenheit. The sunroom/thermostat payload is a number representing the setting the thermostat was last set to.

 // if temp is less than thermostat turn on heater.
flow.temp = flow.temp || 0.0;
flow.therm = flow.therm || 70.0;
 if (msg.topic === 'sunroom/thermostat') {
  flow.therm = parseFloat(msg.payload);
} else if (msg.topic === 'sunroom/temperature') {
  flow.temp = parseFloat(msg.payload);
} else if (msg.topic === 'heater/state') {
    flow.state = msg.payload;
}
// add a dead band, if on turn off 1 degree late
if (flow.temp < flow.therm) {
    // msg.payload = "on " + flow.therm + " " + flow.temp;
    msg.payload = "on"
} else if ((flow.temp > flow.therm) &&
           (flow.state === 'on')) {
    //msg.payload = "off " + flow.therm + " " + flow.temp;
    msg.payload = "off";
}
return msg;

There is only one thing output from this, and it indicates if this wants the heater "on" or "off". The output of this is determined if the temperature is less than the thermostat (flow.therm) the payload is sent as "on". If the temperature is greater than the the thermostat setting, and the heater is currently on (flow.state from the heater/state topic) then the payload is set to off. If the temperature matches, it does nothing.

Sometimes the sensor is right on the edge 72degrees/73degrees and it jumps back and forth, so the heater turns on and off frequently. Leaving the sensor to not do anything if the temperature matches the thermostat setting allows the heater to have some hysteresis, and take maybe a minute to change states.

The output of the check thermostat goes to the heater/gas topic, listened to by the nodeMCU connected to the heater itself. There is also a debug output and it is handy to have while debugging things. The function code allows additional information in the payload to see what the current temperature and thermometer settings are when changing state, but that will only work with the debug turned on.

The blue boxes are for the dashboard. The current temperature is a gauge_ui element, and is at the top.

The slider under the gauge is the current thermostat. This is a pass through UI element. It will adjust based on messages heard on the "sunroom/thermostat" MQTT topic, and will send values through to the heater thermostat topic.

The settings look like:

There is also a text output that will show the current thermostat setting. The UI is a relative bar, and no other indicators. I typically add the text items so I know what the slider is pointing at.

I have two switches, both pass through. The current heater state is indicated by values coming in on the heater/state MQTT topic. Clicking this button on or off will output the state to the heater/gas MQTT topic turning the heater on or off (manually). The light on/off is similar sending on the heater/light topic and indicating the debug on/off buttons.

There is a filler UI element. Without the filler the UI sometimes randomly wrapped funny.

That is something to play with to get the widgets. to align properly.



A keen eye might notice a connector widget in the middle of the flow that I didn't mention. This is for the voice input. Yes, from my phone, a Google assistant or other device I can control my house by voice. That is for a future post.