Picture of Computer Controlled Power Switch
Want to toggle a power outlet between on or off with your computer? How about doing it with a remote? Sounds nice - I know. But the best is that you can make it all, and this will tell you how...

"Why would I want to turn a power outlet on or even OFF with my computer...?"

Ever stub your toe getting out of bed to pee in the wee (tehe) hours of the morning? Enjoy mood lighting? Hell, maybe you just want to be a dweeb like me? This will make your life a little more easy, and if it doesn't do that it'll still make you super-swanky.

The great thing about this project is that it's not limited to a light - this is a computer controlled POWER OUTLET. So long as you're using a simple house-hold appliance this project is for you.

What makes this even cooler is that you can control 8 things with your parallel port (there are 8 data pins). So if turning a light on and off isn't enough for you then you can, potentially, turn your room into a TECHNO DANCE BAR!... or not.

You have to understand, before you try any of this, that I'm not responsible if you get injured; if any of your property is damaged, or if you get shocked - lighting your clothes on fire and turning you into a screaming human candle - I'm not responsible. So, please, be careful and pay close attention to any details... it'll save you a lot of annoyance and tribulation.

Mistakes only happen because of the unknown or overlooked... the closer you pay attention to what you're doing the less likely you'll be to make a stupid mistake. I know this because I am the master of stupid mistakes.

You're going to need a few things...
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IOTrav1 year ago

Neat but why not do it from your phone from anywhere in the world like this:


globrite2 years ago
A nice and safe alternative is to use a Wattstopper power unit which is UL approved, has zero voltage switching and as a bonus has DC output at about 150 mA to power your controller. One such unit (B-120 EP) is available from Amazon for about $15. - Enjoy.
manumahajan2 years ago
hello sir, i am test my parallel port power with connect a LED with it . but when i try to off the LED with relais timer ,unable to switch off and on from the software and the LED is always on
Just a little safety info to add on to your really cool instructable. I think it's important to note that with AC power it's a common misconception that there is a positive and negative line. The truth is that AC(Alternating Current) only has a hot and a neutral wire(There should also be a ground wire, but that's really only a safety precaution added in the last 30 years or so. Ground and Neutral are always linked somewhere if only by a very long stretch of earth.) as the current changes polarity from positive to negative and back to positive 60 times per second(60 Hz) in the United States and 50 times per second(50 Hz) for most of the rest of the world as I understand. This next part is important... If you put the relay on the neutral wire, even when the switch is turned off, the hot wire will still have juice, and anyone or anything that is grounded (you'd be surprised at what types of flooring serve as a ground, and yes wood is an electrical conductor if a poor one at that) when it comes into contact with the hot wire will be electrocuted. Unfortunately this is a common mistake with DIY electricians installing new lighting circuits in their homes, and people die every year because someone switched the neutral wire instead of the hot wire. It's another common misconception that if you only touch one wire at a time a hot circuit cannot electrocute you. This is true only with DC circuits. To be electrocuted by an AC circuit you only need to touch the hot wire (and usually be grounded depending on the voltage. High Voltage, like in the lines on those tall steel towers, creates a static field and can electrocute something without a ground. Wow that's more than a little off topic). The point is, there are safety precautions to be observed when working with electricity.
So it would be better if the relay was put in a grounded box?
balbahra4 years ago
Hi. I tried downloading the softwares you used from the page on the last step, but the links seemed to be broken (Parallel Relay Control, and Parallel Relay Controller). Would really appreciate if I can get the files. Thanks for this nice instructable.
User10052734 years ago
I have to say using Rent-A-Coder was genius. The links in this page (Parallel Relay Control, and Parallel Relay Controller) seem to be broken tho, do you have an alternative host?
egriff6 years ago
I'm going to try this with voice activated controls
Stephen_A (author)  egriff6 years ago
Voice activation never works right. You tell your computer to turn the lamp off and your garage opens. I've been using a program called "PuppetMaster" for my Smartphone - connects to my computer via bluetooth. It's very good.
You can use VAC (Voice Activated Command), but if you have Win 7 just use the built in Windows Speech Recognition. Win7's WSR is on par with dragon, and like all of the other Voice control programmes, you will have to train it to your voice. I use it everyday to run most of my house, and once I had gotten 3 to 4 hours of voice training in it performed with about 97% accuracy.
DiCleC4 years ago
So theres a programming language called auto hotkey With that, I can watch a rectangle of pixels, and due to what it sees, it can automatically do keystrokes or mouse clicks.

My question to you, if how quickly the device will respond to your program's controls.

My plan: I have LED Christmas lights set up in my room. If i plug them into this (different strands on different ports) I could *potentially* set up a mic near a speaker and, via auto hotkey, watch the input volume, turning on and off certain strands according to the music volume.

This is all relying upon the fact that the devise reacts in near-real-time. Any recommendations are greatly appreciated.
Hey, Great instructable! heres a question for ya ; could you use the program mentioned to run an appliance for 5 minutes every 2 hours ?? im interested in how complex the cycles can be activated/deactivated and at what rate Thanks!!! good job
rajanpaudel5 years ago
It may be stupid question but as I am not familiar with those stuffs but interested how this works. How can you controll multiple electronics using one relay? I mean I saw just one connection point in the relay you used in project?
DIY Dave7 years ago
AC power is not "positive" and "negative" it is "hot" (power) and "ground".
"Hot", "Neutral" and "Ground"
Stephen_A (author)  DIY Dave7 years ago
You're not pedantic, Dave; you're precise!
Dude you can get that relay for like $10.00 off ebay and 120v will not kill you if you just tap it happened to me lots it will just give you a jerk. @40 will kill you!
 thats why 240 countries have earth wires. 
gophergun5 years ago
Is there any way to do this wirelessly? I'd rather not have wires going out to the living room.
w477s5 years ago
hey! you have same relays i sell! :P opto22 ftw :D
btw i used once and i saw that 3 and 4 (powerup for relay) has destroyed mounts for screwing it xD i soldered cables inside :P
benjgvps6 years ago
What is the closest alternative relay on http://www.digikey.ca/ ?
As well as the cheapest that can run a space heater.
Stephen_A (author)  benjgvps6 years ago
Space heaters typically require a pretty high amp rating, may want to be careful and check all the stuff you look at before you buy anything.
Heh, I actually made this already.


I have not tried the space heater yet. I am using digikey part number 365-1484-ND, which has a 10 AMP rating, is that enough?
Stephen_A (author)  benjgvps6 years ago
It should say on the CE label what your space heater is rated for. 10A sounds promising, but it could fry your relay over time even if it's only a little above the relay's rated specifications. Let me know how it turns out :)
Drat, It seems to be 12.5 AMPs. I may eventually upgrade the relay in it.
cooldog7 years ago
okay great Instructable one question if you hook up pin 1 to the relay which id your return wire
Stephen_A (author)  cooldog6 years ago
I'm not sure offhand, but if you use that german/dutch/whatever software I link to in my instructable... then you can debug which pin it is :)
Flumesoft7 years ago
Are there any relays that can be brought on jaycar.com.au or dse.com.au that could be used for this project. Also what voltage can the project range from?
Stephen_A (author)  Flumesoft6 years ago
Project can be practically any voltage DEPENDING on your relay. I didn't check the sites but I can tell you that you'll have to pick your relay depending on the project. Basically all the relay does it take one circuit (computer, for example) and turn on another when voltage applied. Some relays are designed to withstand minimal voltages on the relay side, others can handle very high voltages. If your project is just a lamp you can check the amp rating on it and buy your relay based on that. The one I listed in my project is pretty heavy duty (which is why I paid $40 for it... smaller ones are only $10!). If you're thrifty you can scrounge working relays from old cars, washers, lots of stuff.
maxpower496 years ago
on the Parallel port conection do you conect 1 or 2 wires and if your computer does not have a pinter port could you use a Parallel Port Adapter like thisto go from usb to parallel
Stephen_A (author)  maxpower496 years ago
Didn't check your link, but if you look up in the comments someone else had the same question about the using a Parallel Port adapter - should be fine. You want to hook ONE of any of the output pins on the parallel port to your relay.
I've been searching and searching for a way to use a USB cable instead of a parallel port cable (mainly because my laptop does not have a parallel port). Is this possible? and if so, how could it be done?
Stephen_A (author)  cgmalantonio6 years ago
You can use a parallel port USB adapter - basically just a parallel port you can plug into your USB port and windows will emulate all the come (parallel) port stuff for you. They're pretty slick in concept but a lot of times the drivers are pretty poorly coded. Check out ebay and stuff, they're really cheap (so no huge loss if the drivers suck on the product you buy). I've been getting a lot of feedback on this project over the last few months. It's really out dated and there are a lot of products on the market now to make this stuff not only more safe but much more flexible - like controlling your entire house with existing power lines. Maybe I'll do an updated Instructable so keep an eye out over the next few months.
awesome! thanks a lot stephen_A that's just the answer i was looking for. Truth is, the experiment i had in mind is starting to become expensive, i am not new to computer programming but i am some-what to hands-on hardware development and circuitry (which is why i figured id start with something simple like this). I've been trying to bridge the gap between computer programming and computer engineering with little success (few modded xbox360's and ps3's, nothing spectacular yet). ANYWAY let me get to my point, this experiment you wrote up is great, i love it, but in my case..i think i am better off buying an adapter from "insteon" instead of investing what little money i have in a project I'll probably find a way to mess up (lol I'm just hatin on myself today).

Again, thanks for your time! I'll be sure to keep up with your posts
Stephen_A (author)  cgmalantonio6 years ago
Any news on your progress? I'm still looking at the Insteon stuff. :)
meauummels6 years ago
i dodnt get it to work ive search evey thing my pin are hoked up correct but it dont works help
Stephen_A (author)  meauummels6 years ago
Where'd you get your relay from? Could be busted. How'd you check your wires? May be miswired.
fkuk6 years ago
can you wire a relay which is powered from the 5v from usb and once the computer turns on the 5v to the usb is there turning on the relay which turns on the power could this work?
Stephen_A (author)  fkuk6 years ago
Yeap, but that'd be boring.
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