UPDATED: RF Remote Control Power Button

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Building this simple mod is a few hours of work, below are the schematics for the receiver and transmitter. The project does, however, require some soldering so gain access to an iron and brush up on some soldering skills. The transmitter is easiest to build so start with that one first. I also used 8-SOC sockets for the encoder and decoder ships since my soldering skills are a bit rusty.





The Transmitter

The RF transmitter is the easiest so begin with that part of the project first. The generic PCB I used has a run of two copper lines down the center, I used one for power and another for reference ground. This makes it a bit easier to manipulate the components around and have easy access to psuedo – power bus. I chose bit 3 (pin D3) as the defining digital line, you can choose any digital pin on the encoder you want, when it comes time to build the receiver ensure you connect up the base of the transistor (see receiver schematic) to the same labeled pin. I start by connecting all the grounds and pull down resistors using the 8 pin socket, all pins must have the pull down resistor, these are simple chips and the digital pins will float to unknown voltage and give you sporadic signals at the receiver. All digital pins must have the 100k Ohm pull down resistor, including the digital pin you choose to definite your relay switch. I then wire up the transmitter to the digital out of the encoder.

Finally, I pull all the power (+5 VDC) pins to the momentary push button switch. This is done intentionally since the transmitter will be powered by battery, there is not point in applying constant power to the entire constantly, this configuration will only power the circuit when a transmitted button press is desired and extends the battery life of the device. The last component is the antenna, which if you plan to operate > 10-15 feet is a necessity, if not then the antenna can be skipped. Since my particular application requires 20 or 30 feet through a floor and a wall, I used approximately 6 inches of wire and tucked it away around the PCB.

Powering the transmitter can be a bit tricky, the transmitter itself is able to handle a large voltage range (2 to 12 VDC) but the encoder can only handle 5 +/- 0.5 VDC, this drove the choice to use a 3 AAA battery pack, one could use a 9 VDC battery (making the build a bit more compact) but this would increase the costs as a 5 VDC voltage regulator would be needed for the encoder. Three AAA batteries provide plenty of power, albiet on the low side of the voltage spec, and the circuit is low power enough that is will last months if not years on the same batteries.

The receiver

The receiver is a bit more complicated, again using the same generic PCB, the center two runs of copper are used as power and ground busses, the decoder and receiver were wired to power and ground first. Unlike the transmitter, the receiver needs constant power in order to listen for the ‘button pressed’ event. Again, unlike the transmitter, the only digital pin that needs to be connected is D3 (bit 3) or what ever digital pin you used above in the transmitter, the remaining digital pins are not connected. The schematic should be straight forward, the data out pin of the receiver is wired to the digital in of the decoder. The digital pin in use is then wired through a 10k Ohm resistor to the base of the switching transistor, while the emitter is wired to ground. The collector of the transistor is wired to the coils of the mechanical relay, which is in parallel with a diode (to prevent fly back).

Finally, use a DVM or relay diagram to determine which pins to common of the relay is normally open, this should be wired to a 2 pin through hole male header, I used 4 pins total one for the power button of the case and one for the SPDIF cable that will basically connect from the receiver to the power switch header on the motherboard. This enables powering up using either the remote control or the power button on the case. Like the transmitter, I also installed a 6 inch antenna and wrapped it compactly around the PCB.

Powering the receiver is easy as well, but requires a bit of work. The ATX 1.1 and higher specification provides for a constant 5 VDC line with 1 A minimum (2 A recommended) capabilities. This 5 VDC stand by line (purple wire on any standard ATX 24 pin cable) is used to power the motherboard components even when the computer is powered down. This is the perfect situation, since the PSU can provide all the constant power to the receiver that it needs. The actual receiver consumes much less than 1 A (less the 0.1 A in actual use) and typical motherboards do not pull much more than 0.5 A on this line. Finishing up the project, I soldered in a male header for typical 12 VDC case fans to the receiver and modded an extension cable by cutting off one end and splicing it to the purple (+5V DC) and a black (GND) wire from a ATX 24 pin extension.





Finishing up

The final results are not too impressive really, the PCBs themselves are slightly larger than a credit card and a bit unsightly, but either could be cut down if needed. One could creatively find a way to mount the press button and transmitter, the receiver can easily be mounted with some spare stand offs inside the case near the edge of the motherboard or, as I have found easy enough, using velcro sticky tape — ensuring that I do not short out the circuit on the back.





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