Hello!
I've been playing lately with picaxe chips, and for a first project desided to go for a boiler controller.
The boiler in question is an wood fired underburning type. You fill the hopper manually with firewood. The boiler is used to heat up a 4000 l of water reservoir, heating of the boiler is required once per day during winter. The boiler is like this one pictured here:
![](http://www.otherpower.com/images/scimages/8104/underburn1.jpg)
The principle for control is, that i control the primary air intake, and the secondary hatch is open all at all times. Because of the rather large reservoir, i only need to make sure, that it's burning with good enough draft for it to burn cleanly, but not so hot as to be wasteful. So i control the draft based on the fumes temperature.
For controlling the hatch, I have an old stepper motor stolen from a broken scanner. The stepper motor drive circuit is also stolen from the same scanner. The whole system looks like this:
![](http://www.otherpower.com/images/scimages/8104/controllerandstepper.JPG)
For measuring the fumes temperature i use a PT-100 resistive sensor. It should be good withstanding for up to 600 degrees C
![](http://www.otherpower.com/images/scimages/8104/pt100.JPG)
The "brains" of the project is the picaxe-18x chip. I assembled it and the small amount of other components required on a veroboard. The cool looking green pcb is the scanner controller board, but I'm just only using the L6219 stepper control IC of it... The L6219 requires several aux components to work, so i decided it was easier to just broke the original control lines, and solder the control lines from the picaxe to the pins directly.
![](http://www.otherpower.com/images/scimages/8104/insides.JPG)
The circuit schematic can be found behind the link, it's too large to display here so I put it behind a link.
http://www.anotherpower.com/gallery/My-electonics-stuff/kytkis?full=1
The basic code for the picaxe can be found in my files under the name "stepper.bas"
So far the controller is working fine, holding the temperature around 270degrees C- It's a bit on the slow side in the response time, but usually not very fast adjusting of the draft is not needed anyway.