Jake writes “When the temperature controller on my $50 garage-sale hot tub failed I balked at springing for another electro-mechanical thermostat so I built this one using junk box parts with the help of that classic: The Engineer’s Mini Notebook – Op-Amp Projects from Radio Shack.” Link.

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Do you think this will work with a water bed (desired temp around 90 degrees F)? How close does it hold the temperature?
It holds the temp to one degree or better, the thermometer in the tub just doesn’t move. I’m sure it would work with a waterbed.
It holds the temp to one degree or better, the thermometer in the tub just doesn’t move. I’m sure it would work with a waterbed.
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Make: School’s Out! Summer Fun Guide
This Summer Fun Guide is brimming with over 50 projects for kids of all ages. You’ll also find inspiring young maker profiles, as well as tool reviews written for and by kids! Plus, it’s our 3D issue, complete with 3D glasses and tons of super-cool 3D photos!
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