This project allows you to control upto eight lights, or other electrical equipment, via your computers printer port. It should be noted, however that this project will not work with serial to parrallel adaptors or usb to parrallel adaptors. Similarly it should be noted that users of windows XP and Vista may find the programs that are recommended will not communicate with the parrallel port. It may be beneficial to resurect an old PC running windows 98.
First of all it is worth knowing a bit about what a parrallel port can offer the electronics experimentor apart from printing stuff.
The parrallel port has 8 useful output lines these are pins 2 to 9 and pin 18 is used as ground or 0v, each output can supply upto 12mA but it strongly recommened not to run anything more than an LED via the pins on there own.
To make the ouput lines useful they must be isolated or buffered from the computer so as not to damage the port from stray voltages. This can be done in two ways, firstly you can use optoisolators or optotriacs, or secondly you can buffer the output using discrete ICs.
The latter method is utilised in this project and will be described in this article
To actually communicate with the outside world you first need to get a program to control the parrallel port manually, one such program may be downloaded HERE. You may also need an additional driver to be able to control the printer port directly, you can get it HERE
FIRST EXPERIMENTS
The first thing to do is make an adaptor for your computer, I used a parrallel port through connector so I could see what was going on at the computer end of the setup, basically a 10 LED bargraph display was cut into the top of the case and connected to the output lines so that it was 'piggy backing' the output lines (the end two LEDs were left inconnected). The picture below shows the internal and external views.
"HITTING THE BUFFERS"
To buffer the outputs from the port two non-inverting 4050 buffer ICs were utilised, these provide 6 buffered lines per IC. A diagram of the connections are detailed below
The diagram above shows the connections for port 4, this setup needs to be repeated for all eight channels.
As is shown in the diagram an NPN transistor is connected to the output of the 4050 and can then be used to switch a relay, it should be noted that the diagram doesn't show a reversed diode connected across the relay coil.
The circuit can then be mounted on a suitable PCB or stripboard, the prototype shown below was constructed as seperate modules with the buffer and transisitor board seperate from the relays.
The connections on the top of the board are the outputs to the relays and the connections on the bottom of the board are from the printer port, I made a 25pin to 9 pin adaptor lead to allow for easy connection to the chosen case.
The relay board was made from 8 surplus 12v relay modules, they were all mounted on a plain board base and were wired back to a 12-way molex header at one end of the board, at the other end I mounted an old type LED dot matrix display and each LED was connected to an individual relay to give an indication of relay state. The completed relay board can be seen below;
When all of the boards are complete they need to be fitted into a suitable case, bearing in mind that there will possibly be eight mains cables connecting to the relays so plenty of room is needed.
The final case that was chosen for the prototype was the second choice as the previous case was too small. Aswell as having plenty of room for connections the second choice of case already had a transformer and PSU fitted so was an ideal choice to power the buffer and relay board. The assembled controller can be seen below;
To achieve automation there are two programs that I would recommend, they are Discolitez which is a plug-in for Winamp that makes the outputs change to the beat of the music. Alternatively a fully programable utility is icicle which allows you to create 'scenes' and dancing light effects.
Additional Disclaimer: www.lightsalive.co.uk and it's affiliates cannot be held responsible for any damage to computer equipment that this project is connected to, your attention is drawn to the disclaimers page
