Introduction: How to Remotely Turn on Any Device E.g. a Computer (with a Cellphone)

About: I love solar powered projects, electronics (µCs) and most recently 3D printing.

In this instructable I'll show you how to turn an old cellphone into a remote power switch for your Computer. For other devices see last step.
This is almost free, if you have an old cellphone and a SIM-Card.

What you'll need:
- Old Mobile Phone (will be, most likly, unusable after this)
- photointerrupter (found in many devices*) or opto-isolator
- A little wire
- Solder iron

The schematic is very easy (see first picture).
You take the vibration-alert power to power a LED, that LED makes a photo sensor conductive, which is the same as you press a button. So you put the photo sensor paralell to the "normal" power switch.

I tried to use a transistor first, but it turned out, that it is way harder that the resistance is big enough if the telephone doesn't ring, but is low enough to turn on the computer if it does. So I used the photo sensor.

mpozzo94 had the problem, that the Computer would constantly turn on and off. My reply to that was:
"You try to emulate a switch, so when there is no input you want it to be non-conducting. Test this. Actually the light sensor only increases the resistance, when there is no light. Maybe the resistance is just too low.
You can try different optos/photoelectric switches/transistors. [...] As well you can buy [...] all of these pretty cheap (few cents).
Using a transistor will require a small curcuit like [ ] (or just search for "transistor as switch"). If this still does not work, you'll need to use a relay (with a pre-amplifying transistor. If it comes to this, you can ask me again how to do that."
His solution was: "[...] I added a few resistors (3K Ohm total) to the circuit shown in the instructable and it works great! Finding the right amount of Ohm was trial and error. Too much never powered on the PC and too little powered on the PC constantly.[...]"

I want to emphasize that this is kinda a quick-and-dirty-solution. But it works and the risk of harming your computer (or other device) is quite small. There are also software-only solutions to this, like wake-on-LAN or teamviewer. These work fine, but require some annoying configuration (and internet-access).

I'm not responsible for any damage or harm done resulting by following this instructalbes.
Using an iron or any other tool can harm you. Warranty of all involved devices will most likly void. Also all involved devices can, as usual, break during this process.

* E.g. CD-/DVD-Drives, printers, casette-players, etc. Mostly in those with mechanical components. But I reccommend just buying a optoinsulator for a few cents.

Step 1: Step 1

We first solder the wires going from the light sensor to the computer/mainboard.
Many computers have something like the thing shown in the image on the mainboard. If yours does, just solder your wires to the PWR/POWER SW/POWER (or similar) and the GRD/GROUND/(-) (or similar) pin.
If your computer doesn't have somthing like that, you can direkly solder to the main board (you'll lose guarantee and you can damage your computer) or you can strip of the isolation of the wires from the normal power switch and solder it there. If you want to be very careful you can also use needles, solder this wire to them an put them into the cables from the switch.
You can test your setup: If you put together the end of the wire, the computer should boot. If it doesn't contact me.

Step 2: Step 2: the Opto

Now take your opto-isolator or photointerupter and solder two wires to the LED (normaly the -|>|- Symbol) and on the other side solder the ends from the power switch.
Mark the wire on the minus-side of the LED/cathode ( this -|>|- not this).

Step 3: Step 3: the Cellphone

Next, we have to solder the wires from the LED to the vibration alert motor.

To do this, open the cellphone. Only screw the screws and don't destroy the cellphone by (e.g.) trying to open the antenna. After removing the screws (remember which was where) use e.g. credit card to open it.
Then find the little vibration motor. Solder your wires to the contacts (if the vibration motor is soldered to the board you have to remove it first). Here it is important to look for plus and minus (you take a voltmeter or just give it a try, you hava a 50/50 and if it doesn't work change the polarity), thus LEDs have fixed plus- and minus-pins.

Close up the cellphone again, put in the battery and turn it on. Then switch of ringtones and choose vibration alert as continous.

Step 4: Step 4: Final Step

Put the pins on the little white thing (step 1) and put this one the mainboard.

Then only put the cahrging cable into the cellphone. If you call your phone, the LED should turn on, reducing the resistance in the light sensor, thus emulating the pressing of a switch and therefore turn on the computer.

Now you can install Teamviewer to remotly controll your computer (put it in autostart and use the "Remote access to unattended computers"-options).

Just some final words on the SIM-Card: SIM-Cards are very cheap (on ebay for 1-5€), but if you don't add credits they usually will stop working after a year. So buy every year a new one or add some credits from time to time.

Have fun with this setup!
If you have any questions/suggestion/critc etc; Contact me!

P.S.: Sorry for any mistakes; My english is a little rusty since I had a really bad teacher in school :D
And I know, this instucables is not very good - maybe I will make it a little nice if I have some more time - but I hope it helps :)

Step 5: Other Devices

If you want to use this instructables on any other device check the flowchart.
In case of the Toggle-Switch you'll have to replace the switch by the circuit and add an pushbutton parallel to the cellphones opto.
See in the "schematic" above.

If you want to do that, and lacking knowledge, let me know.
If you made it, let me know :) (And if you have, send me the schematics, please :)

> Flip-flop-Circuit
> Switch types
> Flowchart: