Felipe La RottaFor the average Joe, “Controlling stuff using computers” sounds like a very Geeky and boring topic. That is because these systems are usually found on factories or inside complicated equipment, hidden in black boxes. However when computer control jumps to everyday life and works along with industrial design, the result is outrageous!
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In this post we are going to make a very simple version of the system. Of course, forget about wireless and iPhone capabilities!! I’m by no means an electronics expert. But I hope that once you understand the basics, you can easily try more complicated and capable systems (beyond the scope of this blog).
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Ingredients
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Ok, enough Prologe. First ingredient you’ll need is an old computer. I’ve choose a PC running Windows XP.
Check the back panel. The computer should have this connector, it’s called Parallel Port. It was used to connect Printers, Scanners, and similar devices before the USB technology came out. As you can easily guess, is obsolete by today’s standards.
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How does the port work (in layman terms)
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I’ll give you a very simple explanation. The holes (technically called pins) are numbered from 1 to 25. Watch the drawing!
The computer program can turn each pin ON or OFF according to the needs, just like switching a lightbulb.
An external device (an old printer for example) is constantly cheking the port to know what the program wants to do.
Each combination of pins turned ON or OFF means an specific message for the printer, like:
- “Print the H character”
- “Print the I character”
- ”Print the ! character”
The communication is bidirectional, the printer may also send information to the computer using specific pins.
- ” DUDE! I’m out of paper!”
But we’ll talk about that on another post
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Controlling the port
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The port can drive other devices than printers, but Microsoft Word will never allow you to do that:You will need a custom program to turn each pin ON or OFF.
I’ve made my first tests using a great program written in Visual Basic 6.0 by Josh Gaby, here is a link to the code. I know VB is old as hell, you are (obviously) free to use any alternative you want. For example, you can find a C++ alternative on the same website
To see the results on the real world we are going to use a couple of LED’s. Make sure they can withstand 5 volts (attaching a in-series resistor may be a good idea, but in my case it wasn’t necessary).
Snap your LEDs anode (+ leg) into any of the data pins numbered from 2 to 9. The cathode (- leg) can go into any of the ground pins, ranging from 18 to 25.
Turn ON or OFF your desired pin…
Hell Yeah!
Very easy.
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Controlling small devices
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All you have to do now is replacing the LEDs with your microwave oven, dishwasher machine, 10000 watt stereo… NO, WAIT! is kidding. Attaching any significant load to the parallel port will ruin it.
In order to drive any decent load you need to use a transistor
This circuit is very good for flashlight bulbs, toys, and stuff like that. The transistor amplifies the small signal coming from the parallel port, and uses it to turn ON or OFF the device. The load should be connected to the third leg (collector) of the transistor.
Controlling 8 different devices require 8 eight independent circuits, each one connected to its respective Pin (that’s why you can see eight transistors). I’ve added some LED’s to increase the “hi-tech” apparency, but that’s optional
This circuit requires 5 volts from your computer power supply (check the schematic). You can get them easily from any spare molex inside your PC, choose the red wire.
I strongly suggest you to cover the other unused holes (black-black-wellow). You may become distracted and plug the circuit into one of them… not funny
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Controlling mains power
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All the examples shown here are a description of my own project, you are free to use any method you want. Whatever you do, you MUST use proper materials and follow your country’s electric codes. Please check the liability section of this blog.
The transistor described on the previous schematic is used to drive a Relay. Pick the adequate voltage and current rating for your load!
PS: The matches shown on the picture are just for size comparison
I’ve connected my circuit in series with the wall switches.
I’ve (temporarily) mounted the circuit inside an old Playstation case. As you can see, there is plenty of room inside to add the remaining 5 Relays.
I’ll use a proper case when everything is finished. If you have any questions please leave a comment!
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Expansion
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The parallel port can drive 10, 20, 50, or even 100 independent devices using an electronic trick. If I have time I’ll write about that later
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My personal project
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(REMOVED FOR IMPROVEMENTS) I’ll add it later
