Computer-Controlled Woodstove

I built this stove and controller in about 1985. It uses a Sotz barrel stove kit with home-made legs, a Sotz catalytic convertor (now defunct), and a Radio Shack Color Computer (COCO) to control the draft.

There's a home-made Interface Box that amplifies the signals from a thermocouple in the stack and a thermistor to get them to the 0-5 volt range for the COCO's joystick ports. It uses a quad Op-Amp and other components from Radio Shack. There's a 24VDC power supply to operate the solenoid draft control, indirectly from the cassette relay in the computer.

You can see the front of the stove with the custom door latch and draft control. A closeup side view of the draft control shows the 2 aluminum heat shields and the damper plate (a 1-quart paint can lid). A closeup of the rear shows the thermocouples inserted into the stack. The lower one is used for control, the upper one was used to tell when the catalytic convertor lit off. The catalyst has died, and Sotz is no longer in business, so we don't use it these days.

The COCO sits on a stand nearly 20 feet from the stove, with a 12" TV for a monitor. It's nearly never turned on, as I seldom have to touch the controls, and I know the keystrokes by heart anyway. It's running a BASIC program that I wrote that's probably 80 lines long.

Here's a page with a very complete description of the stove and its operation, including the actual operating program.

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