Credit: original idea inspired by Marsupial at GIDEONTECH (at least that was the first place I saw in 2003)

HTPC (Home Theatre Personal Computer) has been a rising idea back in 2003. Still today, not many people are investing in HTPC. People think they might have HTPC of their own but I am talking about the real HTPC--one that you can treat it like your DVD, VCR or Home Threatre surround sound system.

What really makes HTPC? There are several components that truly makes an ordinary PC to HTPC. From time to come I will be making complete posts of my HTPC. But the very crutial part of HTPC is to make it completely wireless!

There are wirelss connections (WiFi) and keyboards...but what about a remote power on? The parts sold by many computer companies are too expensive and it takes PCI slots that you may or may not have available. Why? Some HTPC requires to have micro-ATX or sub-ATX motherboards. Every PCI slot counts.

The original idea and the article inspired me to make my own remote "control" to power on my HTPC. This only took a regular wireless doorbell that I purchased from a local hardware store, a reed relay from RadioShack and various parts I wanted from leftover computer parts.

Step 1: Solving the constant power issue

A computer does not remain a constant power supply until the power button is pressed. To solve this issue the majority of motherboards have WOL (Wake On LAN) that constantly powers the NIC in the event of remote request. Luckly this provides good 5 volt supply at all time--even with PC turned off.

I accessed my BIOS and enabled WOL or BOOT POWER - PCI device for some other motherboards. Please refer to your motherboard's manual for complete guide to enabling this portion. *Some motherboards will not start unless this device is actually present. This means, if you enable it before you plug in this WOL to another device, your computer will not start and just hang. If this is the case, enable this option at the END of your steps.

Step 2: Planning ahead

If you are not familiar with circuit boards or soldering please practice before you follow my project guide.

I wanted to create a circuit board that not only require to have wireless power on switch, but a manual override switch. This means I can either use the remote control to power on OR press the power button, physically, and turn my HTPC on. This requires to have two connection that are open circuit until the relay or the button closes the circuit.

The power button to the motherboard is nothing more than a momentary switch (pressing will cause to close the circuit and releasing the button will cause to open the circuit) extending from the motherboard. And as we all know, if you hold the power button for over 5 seconds, your computer will perform a quick shut-down. Which means, my doorbell cannot "ring" for more than 5 seconds.

Step 3: The doorbell

Many doorbells have different options: "ding" "ding-ding" and "melody playing" For my remote control need, I need a straight "ding" that is no more than 5 seconds long. I have found one for $5 that was in the clearance bin. I opened the recever (one with the sound coming out) and checked the operation using my Craftsman voltmeter. I checked to see the continuity and voltage. Again, I was in luck! The doorbell receiver only requires less than 5V and can sustain operation up to 7V.

Step 4: Finding the right relay

Now that I knew my operating voltage (motherboard manual indicates 5V from WOL and doorbell ringing at <5V) finding a relay to operate within 5V was the only hard part left. Reed Relay from RadioShack met this requirement. This relay is SPST (Single Pole Single Tap). This means, when the current is running one direction it causes open "TAP" to be magnetized and taps to the nearest metal--to close the circuit. When the current is not running it returns to the open circuit stage and cuts the connection, to whatever it is connected, off.

Step 5: Circuit board layout

After careful consideration, this is what I came up.



Providing a constant power from WOL to the doorbell receiver, the speaker wires delivers 4V to the reed relay (picture with red box inside--coils). When the current flows through the coil it creates magnetic field which causes "reed" (the open portion on the left) to be attracted to the metal piece and completes the circuit. I then added PINS to connect to the motherboard and to the HTPC power switch. As you can see, I ran 6 pins in parallel formation to keep things simple.

This is the final picture of my remote start receiver.



Step 6: The final count

Complete project is as good as the original intension. If this project somehow short-circuits your motherboard you would have one very expensive mistake to correct. So after completing my project I took my handy voltmeter and checked to see the Continuity and Voltage. I wanted to make sure the contact is made just long enough to turn on the HTPC but not too long to shut itself down. I also wanted to make sure that the connection did not produce ANY voltage. Any current voltage feedback (going back to the motherboard) would surely to fry the motherboard. Because of my planning ahead no currect is flowing at any of those 6 PINS.

When mounting this to your computer case, HTPC case, remember that this may create unwanted current flow. Be sure to mount this on a surface that will not cause any short-circuit.

This took me about 4 hours to build (my soldering technique wasn't as good as before) and inhaled many lead fumes. So be careful when you solder anything The button from the doorbell will be mounted to my wireless keyboard (pictures coming in future posts) and it is working beautifully.

Any questions please feel free to ask. Happy modding!

Very nice in depth tutorial. not used to seeing things like this at Trap17

If I had the skills and the money, I would give this a go
It sounds like good random fun...and I wouldn't have to reach to my pc to turn it on/off

Very nice tutorial

Reminds me of the XBox 360 controllers and the ability to turn on and off wirelessly. Brilliant tutorial and you go into great detail. I would try this but unfortunately I own neither the computer nor the wireless doorbell at my house