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What it is: An Arduino-based light-sensitive switch for turning on a desktop computer.

Why its cool: Use a Sonic Screwdriver to turn on your computer!

Story: This project started, as I'm sure a lot of them do, as a result of boredom and the thought "Wouldn't it be cool if...". I am a fan of Dr. Who. Enough of a fan, I suppose, to spend money on a plastic replica of the good Doctor's Sonic Screwdriver (http://www.thinkgeek.com/geektoys/cubegoodies/8cff/). It was cheap, and it lights up and makes noise _ As a fan of the show (and a CPE/EE), I simply had to have it.

While pondering what to do with my time off, having recently graduated, and while playing with the Sonic Screwdriver, I had one of those "...Duuuuude, Awesome!" moments. And an hour or so and a transistor or two later, I have a device that allows me to do what you see in the video below:


Step 1: The Nitty Gritty

Now we'll get into the technical stuff.

In a nutshell: The photocell is connected in a voltage divider circuit, resulting in a voltage between 0-5V applied to the analog input pin of the Boarduino depending on the amount of light detected. The on-board ADC gives a numerical value based on this voltage. If that value crosses a certain threshold, the digital pin connected to the Base of the transistor is set high, the motherboard power switch circuit is completed, and the computer turns on (or off).

Yes, the circuit can be triggered by any bright enough light source. Like a normal flashlight or, oh I don't know, a camera flash. But its just so much cooler to whip out a Sonic Screwdriver and be all like the Doctor and stuff...Right? Thought so _

A Note: The USB ports on my computer are powered as long as the power supply is on (even if the computer is not running). This provided the power needed for the Boarduino and allowed the circuit to function. I was able to run the USB cable out the back of the case and into a free USB port. Not the best way to power the circuit, I'll admit. I hope to have an updated version of this circuit that provides the same functionality in a more discrete manner. More on that later.

Step 2: The In-Line Transistor Circuit

A relatively simple circuit. Simple enough, even, to unceremoniously slap together and wrap up with a bit of electrical tape. I took off the tape for this picture. You've seen in the previous slide how it looked when finished. The inside of my computer is a rat's nest of wire already. Why not add some more? hehe.

I've said it was a simple circuit. But notice how I totally got the collector and emitter backwards. Yeah. Funny story about me a transistors. For part of my senior design project, we built a giant PVC pipe binary clock. It had 19 LED light clusters, each one needing to be toggled at the appropriate time by a micro-controller. We chose to use a similar transistor circuit that would turn on the light when the pin on the micro-controller was set high. Easy enough. Worked great in prototyping. Worked great all the time, actually. Even as a final product. But one day, our adviser comes in to have a look at the circuit. He asks me to take a look at the "orientation of the transistors."......*facepalm*. Every single one was backwards. But because the current draw of the lights was so low, the circuit functioned fine with the transistors reversed, which is why it never occurred to me during construction. As an electrical engineer, it was a very humbling experience. I told myself I would never make the same mistake again. mmmBahaha. We see how well that went...

(P.S. I hope to have another Instructable up eventually detailing the construction of that clock. Stay Tuned!)

Step 3: The (Bo)arduino Program

So short, It'll fit here. Based on one of the sample programs in the arduino library. Note that the '< 20' bit can be changed to make the circuit more or less sensitive. Having taken the thing apart for this Instructable, I can't, for the life of me, remember which direction results in higher sensitivity (i.e. whether a higher or lower number makes it more sensitive). My apologies. When I throw the circuit back together, I'll update accordingly.

//Sonic Switch Code
int analogPin = 0; //pin a0 on the board
int ledPin = 10; //pin 10 on the board
int analogValue = 0; //value from the ADC

void setup()
{
pinMode(ledPin, OUTPUT);
}

void loop()
{
// read analog input, divide by 4 to make the range 0-255:
analogValue = analogRead(analogPin);
analogValue = analogValue / 4;
if (analogValue < 20){
digitalWrite(ledPin, HIGH);
}
else {
digitalWrite(ledPin, LOW);
}
delay(10);
}

Step 4: (not So) Final Thoughts

Looking at it, it seems like a bit of overkill to use the ATMega168-powered Boarduino for such a simple circuit. I had toyed with the idea of trying a purely analog (no micro-controller) circuit to give the same functionality. I suppose it could be done, given the right component values and configuration. But I wanted to have the "Only On or Off" capabilities that a transistor triggered by a digital output pin offered. And I had a micro-controller lying around not doing anything and knew it would be easy to use it to get the desired effect. But I'd definitely be interested to see if anyone has any thoughts on a way to do this using just discrete components. Analog circuit design wasn't my strongest area of study (go figure, huh? hehe).

But I loves me some AVR chips (apparently). I recently purchased a USBtinyISP programmer from Adafruit Industries (http://www.ladyada.net/make/usbtinyisp/) and a couple of ATTiny25 chips from DigiKey. I've got a few projects lined up that might benefit from the tiny yet powerful ATTiny. I'd love to retool the Sonic Switch to use this chip. It certainly would take up less space and not add as much to the clutter already present in my computer. I'll be sure to detail the project in full once it gets underway.

If you've made it this far, thanks for reading through my first Instructable! I welcome any comments, questions, and constructive criticisms.
<p>I usually use sleep mode instead of turnoff so i can turn my computer on by clicking on my mouse. Could i maybe hook it up into my mouse or something?</p>
<p>does it work with the towerless iMacs made in 2011? I forgot to get the upgradable Mac Pro tower</p><p> so I can't really do this easily :P.</p>
Possibly, but not without taking the thing apart. I've never cracked one open so I'm not sure how easy it would be.
Hello fellow whovian. Could this be used to turn on a phone or tablet? Thanks! I will DEFINITLEY be using this if I go to the comic con in my town.
Does this work on computers without plexi-glass sides?
Now that I think about it, sunlight would turn it on too...
Can you not just put in a UV receptor? Do those even exist?
why disable the switch? you could just wire in the borduino in parallel with the switch <br>
I would never turn my computer on another way. That would never, ever get old. Brilliant, now I know what my next project will be.
wow use the aurdino controol on a door and open doors around your house
I would SOOOO do that.
ok thanks now how to do it
Instead of USB power it through the nearest outlet to your door. Then on the hinge side of your door drill out a hole. Stick the photocell in the hole and put a plastic cover on either side (like a window). Then you hook that photocell up to an electric lock on the door.
well that works good job wait what if someone has a flashlight hmm
Put it on an internal door that doesn't matter and only use it for show. (Or use some sort of voice activation and hope noone can make a sonic screwdriver sound)
Reminds me of something, look up blue box on wikipedia, people could get free phone calls by whistling. Steve Wozinack managed to prank-call the Pope doing it.
you never know
Or mod your Sonic Screwdriver to give off an enormous amount of light and make the photocell not very sensitive.
This is brilliant! I have an IR port on my laptop, and I am going to order 2 sonic screwdrivers, one to keep and one to mod, then I will find a way to make my laptop react to an IR LED in the screwdriver.
You mod the computer, not the screwdriver.
The sonic screwdriver doesn't have any IR, its UV light, to get it to interact using the IR port you would need to mod the screwdriver.
Perhaps, you could add an IR LED in parallel with the UV LED. I don't know if it will fit or not, but if it does, you could still get the blue light as well as the infrared. I might try it once I get one. Right now, I only have the Eleventh Doctor's screwdriver.
ok, I want to do this with RFID chips for all electronics in my house.
The problem with this is that it will start up with any bright source of light like a flash light, camera flash and who knows..........light from the sky(i.e. thunderbolt). So what you should do is replace the light in the screwdriver with an infrared led and the photocell with an infrared photoresistor (or phototransister). That way very few things (like the remote of your tv) can turn it on.....!!!!!
Very awesome! Just got into Doctor Who, and this is a killer project. I would love to see code for ATTiny25. Have a project lined up soon that uses one and would to get my hands on some other fun things to do with that chip.
Would this work for a laptop?&nbsp;
I don't see why not. You might have to do some clever soldering/de-soldering to fix the switch wires and the power connection to the right spot, but yeah, you could do it. <br />
Cool thanks!&nbsp;
I wonder if one could build a function switch into this beauty for dual use. One function being the IR tool and the other being the laser burner described in the instructable link below.<br /> <br /> <a href="https://www.instructables.com/id/Cheapy-Laser-Lighter-Burner/" rel="nofollow">www.instructables.com/id/Cheapy-Laser-Lighter-Burner/</a>
Very nice, I congratulate you- you made a toy that much like the real thing! (now let's see you drive a screw with it! lol)
has anyone seen this?<br/><a rel="nofollow" href="http://www.indymogul.com/post/9066/wesleys-weekly-presents-the-sonic-screwdriver">http://www.indymogul.com/post/9066/wesleys-weekly-presents-the-sonic-screwdriver</a><br/><br/>granted, it's labeled sonic screwdriver, but looks more like a laser screwdriver. yet it's still very cool and simple.<br/>
You know what you could do. Is mod the computer case with a hole that the end of the sonic screwdriver would fit into. Now this hole would have a little door that would add additional insurance on there being an accidental activation of the switch. it would kind of be like the "port" the Doctor put his screwdriver into at the library.
Don't they make a magnetic-sensitive reed switch large enough to sub in for the case's power switch? Seems like that would be the simplest approach... Just a thought.
But....But then you wouldn't need to press the button and make it light up and make noise...... hehe. An idea, true. Maybe not for this project, but now that the existence of such devices has been brought to my attention, perhaps I could use them in some other project. hmm... *makes mental note*
I wonder how small you can make an electromagnet and have it trigger the reed switch. Shouldn't be too tricky since all an electromagnet is is coiled wires anyway, right? (I'm pretty sure, but not 100%) Then it could be on only when you've got the light going. Maybe even work a delay into the electromagnet part so the screwdriver's sounds can mostly finish before the computer reacts for maximum effect. Might also be a fun way to rig an electric lock to a room too... just have a backup way in caase it fails of course... :)
sounds like great fun :P I'm just trying to decide what to do for my GCSE electronics project & i think you may have just solved part of the problem
this is great you should join the <a rel="nofollow" href="https://www.instructables.com/group/The%20Whovians/">whovians</a> group<br/>
I like. L
I was slightly hoping you'd added some kind of IR remote control to your Screwdriver which turned the computer on, but this is also good. What happens when the lighting level in your room changes, though? Can the sun come out and suddenly turn your computer off? (Not that this would be a bad thing, could even be a feature for some people I know :P) I also have no idea how complex it would be to implement the IR receiver, but probably more complicated than this circuit.
From reply above: "As for the accidental triggering, it hasn't been a problem. The activation threshold in the code can be set to a level such that bright, direct light is required. Combined with where it is positioned in the case, there's no risk of accidental activation if, say, the sun is out and my blinds are open. Granted if direct sunlight fell onto the case, it might trigger it. But the way I have it set up, I don't have to worry about that." The IR sensor is an idea. But then I'd possibly have to worry about my TV remote accidentally triggering the switch, hehe.
lol love it!! a friend of mine made a replica, scale TARDIS computer case, it looks fantastic! lol i'll have to show him this. there are tons of ideas to use only your sonic screwdriver to turn it on, instead of a stray camra flash; but i think the simplest would be to use a timer, the light has to be on for over a certain amount of time before it turns on, or off. that, or add in a small IR LED and use a IR sensor...
Haha, TARDIS computer = awesome. I absolutely give the inclusion of the Sonic Switch into the TARDIS case my blessing, hehe.<br/><br/>As for the accidental triggering, it hasn't been a problem. The activation threshold in the code can be set to a level such that bright, direct light is required. Combined with where it is positioned in the case, there's no risk of accidental activation if, say, the sun is out and my blinds are open. Granted if direct sunlight fell onto the case, it might trigger it. But the way I have it set up, I don't have to worry about that. <br/><br/>Hmm, requiring both the Photocell and the IR sensor to be triggered might remove the 'camera flash' problem. I'll consider that, though I would like to avoid taking apart the Sonic Screwdriver if possible, hehe. Thanks for the suggestion!<br/>
I like it as well... Another option might be to listen to the sound of the screwdriver, i.e. the microcontroller listens for a certain frequency. No accidental start/stops and the screwdriver acts like a key.
Great XD
HAHAHA! This is awesome! I love it!

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