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Cheap Thermostat

Discussion in 'Controls' started by Releep, Jan 19, 2013.

  1. Releep

    Releep Elite Member

    First thing is first this is a build for people that are experenced with electronics, or at least comfortable with soldering and tinkering with electronics.


    The components in these plans can at any time be at mains potential.

    Now that all that is out of the way I have been searching for a soulution to temperature control I've looked at all the commercially avalible products out there and didnt like them for one reason or another. Most contain relays and im not a big fan of relays. Which led me to searching for a design on the internet with little luck, untill I found this site, Charles' Cozy Project the plans on his site most likly work for most people. The design has about a 3 deg swing on it and I wanted somthing that was a little more responsive.

    The changes I made. I added a PTC thermistor to increase the rate of change to maintain a more constant temperature.
    I also changed the value of R5 to one more commenly avalible, changed R2 to a higher value to bring the temperature range down a little, the 300k in the original plans will work quite well for a breeder rack setup where the probe will be on the outside of the tubs.

    The total cost of building one was about 15.00 (I already had some of the componets so that is a educated guess.)

    I purchased the dimmer switch from home depot for about 6.00, that contains the 250k pot, triac, the two capasitors, and the rf choke. The rest of the parts I had on hand or purchased from Digi Key.

    Triac Dimmer Thermostat.jpg

    On a side note the thermistors need to be placed in the same location to sense the temperature corectly.
    It's hard to see but both thermistors are inside of the shrink tube.

    I also have the schematic in Eagle CAD files that the uploader wont let me upload, pm me with your email address and ill send you the .sch and .brd files if you want them.

    I forgot to take pictures before I assembled the test box when I move the components from the test box to a final enclosure I'll take some pics and post them.
  2. Releep

    Releep Elite Member

    The board is small enough to fit inside a single gange outdoor light box.
    I placed a piece of plastic shelf liner under the board to protect against a short circuit.

    The dial switch is the one from the Home Depot dimmer.
    A little hot glue works well to insulate the solder joints on the bottom of the switch.

    All closed up.

    I taped the sensor right on top of the heating element.
    The tub will slide right up to the probe.

    When I build the next one I'll make sure to take detailed step by step pictures of the build.

    Attached Files:

  3. kriminaal

    kriminaal HH Block Leader Staff Member Premium Member

    Very interesting, but beyond my scope of electrical.

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