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By rudy
#80987 At work we use 10" LCD panels in a product. The LCD package includes a 12 volt adapter but we don't use it. I decided to remove the power supply and use the enclosure as a ESP-12 based relay.

I have included a red led on the front as a status indicator. The cheapy 5 volt power supply I used in the project has more than enough capacity for the ESP8266 so I also decided to put on a 1 watt white led. I have the 1 watt led glued into the enclosure and I have an aluminum strip behind it as a heatsink. If I had to make this over again I would like to have put the led soldered to the back of the board, using the pcb as the heatsink. That would have eliminated the wires I now use between the led and the pcb. I was in a bit of a rush and didn't have much time to spend on this design. The red status led is soldered onto the back of the pcb.

The relay is a relatively small size, has a low power coil, but still has a 5 amp current rating. I was more interested in lower power consumption over high current capacity. At 5 volts it only uses 40mA. The unusual thing about this relay is that the coil is polarity sensitive. Connect power the wrong way to the coil will not cause it to switch on.

Mostly I will be using it for led lighting, although I have the same relay (in a different enclosure) for switching the power to the block heater of my car.

I also have a microwave motion detection board that I have used to signal the ESP to turn on the 1 watt led. I have a 15 second retriggerable countdown timer to hold the light on. I don't have the microwave sensor board in the pictures. I put it above the AC power output connector. I have it covered in heat shrink tubing.

I have some header pins of extra I/O and power. On some of these modules I will drive some external 5 volt color led strings.

I had laid out the board to include a solder in 1/2 amp fuse in line with the power supply but the initial turn on surge kept blowing it. I then decided to add a 12 Ohm 1/2 watt resistor in place of the fuse. This reduces the turn on surge but doesn't have any significant effect during normal operation. The resistor I used is an old style of resistor that used to be common many many years ago. It is a carbon composition type, rather than carbon film or metal film. The carbon composition type can handle surges a lot better than the more modern types. The specifications lists the turn on surge for this supply at 12 amps. That's pretty hard on the capacitor so I hope the added resistor might increase the life of the power supply components.

I have 10 of these now. I ordered a 100mm x 100mm 10 pieces prototype order from JLC PCB for $2usd plus shipping. This was one of the boards I had on the panel.

Click the images if you want to see a larger image.




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