Monday, January 7, 2013

Temperature Controller

I spoke previously on here about adding a temperature controller to my Black Garlic Oven design, and appreciated CubeConvict's recommendation of the STC-1000. I found this general use controller intuitive in ways, though the software interface is somewhat erratic in its utilization of its buttons.

To illustrate this, consider the hardware connections on the rear of the unit. The connections are all screw terminals, with pairs for power, sensors, cold and hot, in that order. I found this configuration straightforward and appropriate the the application. The software interface, however, offers challenges. The power button is labeled with a standby symbol, which alone is confusing. Furthermore, consider the way to change temperature. On the main screen, one holds the "S" key for 3 seconds, selects a menu item using "S" and then adjusts the setting by holding "S" and pressing "Up" or "Down". When the desired setting has been reached, one presses the Standby/Power button to commit the change.

Thankfully, the unit required very little adjustment. For housing, I purchased a PVC box (As pictured in this MakeProjects post) and added a power outlet and binding posts for the sensors. After splitting the plugs on the power outlet, the unit allows me to simply plug the oven into the "heat" plug.

The binding posts and banana jacks purchased from RadioShack, with the binding posts being advertised as "insulated" (though it would take a far stretch of the imagination to consider these meaningfully insulated). The binding posts are screw-on, and I drilled holes to attach the power outlet. The STC-1000 has mounting brackets included that secure it to the lid. I used disconnect terminals inside to attach the power cord to the controller and the outlet (the electrical tape wrapped bit connection the end of the power cord's sheathing), and spade terminals to provide power to the outlet.

Everything fits easily inside the 4"x4" PVC box that I purchased from my local hardware store. To secure the power cord inside the box, I put two zip ties on the cord and heat shrink wrapped them with a glob of glue inside the tube.

Part of the beauty of this controller is that, in an arrangement such as this one, it can be used to control both heating elements and cooling systems (such as an AC or a chest freezer), allowing it to be used for any application between -50°~90°C. I will likely use the STC-1000 for many other fermentation chambers in the future.

Update (2013-01-07) - Circuit Diagram:
A barebones illustration of the circuit with a heating incandescent and cooling appliance plugged in.

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