The rain and dropping temperatures in San Francisco this weekend reminded me of a project I made in the winter of 2006. This was long before mightyohm.com existed, so I originally documented the project at instructables. I’m not going to repeat everything here, but I wanted to share some pictures and provide a link to the instructable in case anyone else wants to try this at home.
The project involves using a digital programmable thermostat to control an inexpensive space heater. The original motivation for this was that I wanted to lower the temperature of the heater at night, reducing my energy bill, while still being able to wake up to a toasty room in the morning by setting the heater to turn on full blast 30 minutes before I awoke.
Here’s a schematic of the simple circuit I made to interface the thermostat to the space heater. The resistor/diode/capacitor circuit allows the thermostat, which is designed to control an AC load, to switch power to a 24VDC coil relay. A 36VAC
I installed the necessary components inside the case of an old power and telephone line filter, used to protect a fax machine or office copy machine from power surges. The case came with a handy 110V outlet mounted on the front panel which I reused for this project. The digital thermostat mounts to the top cover of the case.
I used a barrier strip as a way to simplify the wiring and mount the few loose components:
I had to adjust the value of C1 to get reasonably clean DC to the relay while not having an annoying turn-off lag when the control line from the thermostat goes low. 100uF works well for the relay I used.
Here’s the finished product installed in my former bedroom:
I haven’t used it since I moved into a house with working central heating, but it sure came in handy during the cold winter I spent in a 100 year old farmhouse in Petaluma. This solved the problem of the sub-50 degree mornings I was having nicely!
instructables.com: Space heater controlled by digital thermostat
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