So, first here is my general setup:
Multiple DS18B20 temp sensors sending data in metric.
One ESP8266 gateway that is using the MQTT protocol.
A mosquitto broker running on an RPi
Node-red running on the same RPi that re-broadcasts the MySensors topics (mygateway1-out/blah) on the Domoticz required one (domoticz/in/MyQTT/blah).
The same RPi with latest 4.97 Domoticz install listening on their MQTT topics. Domoticz is set to use imperial units of measure.
All is working as it should.
Last night I installed HomeAssistant (not HASS.io) on my laptop and set it up to use the MySensors protocol and to listen in on the mygateway1-out/# topics. And, of course, I set the HA temp units to imperial. Messed around a bit and decided that enough was done for the night (could not get it to talk to my smart TV).
I then checked my Domoticz dashboard and saw that, well, my house was turning into an oven! The 2 sensor nodes are now reporting temps of 170F! I look at the Domoticz log and it isn't a transient event. I then look at node-red in debug and see that the mygateway1-out is sending out F values instead of C values and Domoticz is converting the values from C to F...but the numbers are already F - so, yay, I get massive wonkiness!
I go back into HA (fire it up again) and change the units system from imperial to metric and, next sensor report cycle, the values are back to being sent in as C. What the ever loving hell? Let's dig into the code a bit.
In the nodes there is this bit:
// Fetch and round temperature to one decimal
float temperature = static_cast<float>(static_cast<int>((getControllerConfig().isMetric?sensors.getTempCByIndex(i):sensors.getTempFByIndex(i)) * 10.)) / 10.;
Okay, so it asks the controller what it should report in.
But, why did this change with the HA settings change?
If HA was just listening on the MQTT topic what the hell is it doing communicating back to the node to tell it use imperial? Can I turn this off and have HA report the correct value (in C) and unit (convert to F)?
If Domoticz is just listening on the the MQTT topic why is it not telling the gateway to use imperial?
I am very confused by this. If I decide to have my nodes report in F how the hell is Domoticz going to handle that? Do I then have to change Domoticz settings to C to get the real number but have incorrect units assigned?
I really don't think the HA settings - unit change should have any impact whatsoever on the actual number sent from a node. It is purely presentation layer not data layer. There should be a method to tell HA that "values sent are in metric" and if the front end unit is set to imperial it should convert the raw number on HA's side - not change the settings on the gateway.