Based on a number of excellent suggestions I got in previous thread, I have decided to convert all my smart home devices over to ZigBee. I have about 50 switches and sensors on-order at the moment.
One thing I can't seem to find is a controller for my pellet stove. My stove is installed in my workshop, and during the winter, I usually have to run out to the shop in the morning, turn the stove on, then wait for a hour or two for it to warm up.
I'm thinking that I'll most likely need to build a controller for the stove. I had some issues with the mainboard in the stove last year, so I'm fairly familiar with how it works. There area few sensors and relays.
- An on/off sensor for the lid.
- A safety sensor for the hopper (makes sure flames aren't feeding back into the hopper).
- A pressure sensor to detect if the door is open.
- An external temperature probe.
- An internal temperature probe.
- A relay for the igniter.
- A relay for the motor that rotates the hopper.
- A relay for the induction fan.
- A relay for the fan that blows warm air out from the stove.
- A potentiometer that switches the stove on and controls the temperature set point.
I have built a number of custom PCBs in the past, and I'm confident that I could build a replacement for the mainboard that includes a ZigBee radio. This requires a significant amount of design work for the PCB, programming for the microcontroller, etc. I'm also just now learning about how the ZigBee protocol works, so there would be a fair amount of research involved.
My other idea was to build a PCB that essentially acts as a programmable potentiometer, replace the pellet stove's pot with this PCB, and leave the mainboard as-is.
Has anyone here tried integrating a pellet stove into your home automation? How did you do it?
UPDATE: This was actually very easy. The potentiometer that controls my stove acts as a voltage divider. At 5V, it signals the stove to shut off, and at 0V, it's fully on. I just leave the potentiometer in the "off" position, and I added a zigbee relay in normally-closed mode in series with the wire feeding from the center. When the relay is "off," the stove sees 5V and does its normal shutdown routine. With the relay "on," the stove starts up. HA switches it based on temperature from a temperature sensor in the room. Depending on your stove, you might need a pull-down resistor (if it expects GND instead of an open), but it works perfectly for me.
Do you need to control the temperature remotely, or just switch it on? If the latter, could you just leave the existing potentiometer / power switch always in the on position and add a new zigbee relay to cut power to the whole works on & off?
The problem with this is that the induction fan is the same fan that blows the smoke out from the exhaust vent; pellet stoves don't exhaust out a chimney like a fireplace. They require forced induction. When you turn off the pellet stove with the potentiometer, the fan continues running until whatever pellets remain in the combustion chamber stop burning. Simply removing power means that the pellets continue burning, but the smoke and exhaust gases have nowhere to go. They will fill up the stove and start leaking out.
Would it help, to add a switch in the potentiometer path? When you disconnect ground from the potentiometer, will the stove shutdown gracefully?
That could be a simple way..
I think that's the solution I'm going to go for. While my idea of building a custom mainboard does sound like a lot of fun, my main concern is with the code. The factory mainboard has set points where it turns the hopper, disables/enables the blower, etc. I could probably get it close in my own code, but I'm sure there are edge cases the factory engineers found that I would miss. I don't much enjoy the idea of going out to my shop and finding it full of smoke or my stove jammed full of pellets, or worse the whole thing on fire.