Playing with an eBay thermostat module. New data in description!

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• published: 06 Oct 2015
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You can now buy me cake and things to take apart at:- https://www.patreon.com/bigclive Programming info and unbricking info down below. This is a very common and cheap module on ebay. As long as any temperature critical application has a secondary protection against overheating or overcooling then it should actually be usable. The module runs on a 12V DC supply and draws about 20mA or 70mA when the relay is energised. The relay has a set of volt-free contacts optimistically rated for 20A at 125V AC. Probably better used at much lower current and voltage for longevity. Here's the programming info:- A brief press of SET enters the main temperature adjustment mode with the current set temperature flashing. This can be adjusted with the up/down buttons, and holding them will make them auto-repeat. When finished adjusting, the unit will store your new setting and revert back to normal operation after several seconds. Holding down SET for about 5 seconds will enter programming mode. You can step through the program parameters from P0 to P6 with the up/down buttons and use SET to select them. P0 Selects cooling mode or heating mode. In cooling mode (C) the relay will energise and close the contacts when the probe temperature is above the set temperature. In heating mode (H) the relay will energise and close the contacts when the probe temperature is below the set temperature. P1 Allows you to set a hysteresis value between 0.1 to 15 degrees. The hysteresis value is to prevent the relay chattering on and off when the probe is wavering around the set temperature point. For instance, with hysteresis set to the default of 2 degrees, when in cooling mode and the temperature is set to 25 degrees, the relay will activate as soon as that temperature is reached, but not deactivate until the temperature is brought down to 23 degrees (25 degrees minus a hysteresis value of 2 degrees) When in heating mode the relay would activate as soon as the temperature fell to 25 degrees, but would remain on until it reached 27 degrees. (25 degrees plus a hysteresis value of 2 degrees.) P2 Highest temperature limit. Set to 110 degrees by default. This is used to limit the upper temperature than can be set. P3 Lowest temperature limit. Set to -50 degrees by default. This sets the lowest temperature than can be set. P4 Probe correction. Very neat. Allows you to calibrate the temperature the probe is sensing by +7.0 to -7.0 in tenth of a degree increments. P5 Relay energisation delay of between 0 to 10 minutes to limit fast cycling of equipment like compressors. After setting this function the unit must be powered off and on again for the change to take effect. When I tested this it switched after about 35 seconds with a delay of "1" and about 1:40 with a delay of "2". P6. This is an over-temperature limit that turns off the relay and displays a row of dashes on the display. Unfortunately it seems to take priority over menu access, so if you inadvertently set it below your room temperature you can effectively brick your unit. But this is recoverable in two ways. Either unplug the probe to make the unit think the temperature is very low (It displays LLL) and that will give access to the menu again, or use the factory reset function which involves holding down the plus and minus buttons while you turn the unit on. The display will do a self-test showing 888 and the unit will revert back to its default settings.