Matt circuit

Here is a simple thermostat circuit that can be used to control a relay and supply power to a small space heater through the relay contacts. The relay contacts should be rated above the current requirements for the heater. Temperature changes are detected by a (1.7K @ 70F) thermistor placed in series with a 5K potentiometer which produces about 50 millivolts per degree F at the input of the LM339 voltage comparator. The two 1K resistors connected to pin 7 set the reference voltage at half the supply voltage and the hysteresis range to about 3 degrees or 150 millivolts. The hysteresis range (temperature range where the relay engages and disengages) can be adjusted with the 10K resistor between pins 1 and 7. A higher value will narrow the range. Electronic Thermostat and Relay Circuit Diagram In operation, the series resistor is adjusted so that the relay just toggles off at the desired temperature. A three degree drop in temperature should cause the relay to toggle back on and remain on...

The world of IoT for “Smart Home” is growing very fast. There are various areas of interests from security to automated animal care depicted for instance on this page. I’ve tried to look at the things from the practical point of view. What would be interesting enough to be build as a project and at the same time have a real, quantitive value? It happens that I was always interested in limiting the energy consumption at home. One evening when talking to my wife and trying to get her opinion on my adventures into electronics she said that it would be great to have a heating already on before she gets home (and a cosy, warm place ready exactly when she enters). I guess she said it as a kind of a joke. To her surprise I got attracted by the idea. Hey, why not? With the current state of technology it is actually feasible. Maybe a bit challenging at first sight but still. So this is how it has started. Let’s build a intelligent thermostat that would be off when we are not at home and turning...

The WiFi SSR board project changed a bit and I use classical relays instead of SSRs now. The reason is that SSRs tend to get quite hot when switching larger loads, and the 8A relays I last used actually could be used for max 2.5A load switching with no heat sink.  The high quality relays I now use allow 10A load switching and are rather quiet. I also changed the design a bit so that it would fit in a box (DIN rail compatible) for increased safety. [ ]