Last night I got started on a test project to try making a simple circuit for interfacing with the parallel port on a computer. The parallel port is the wide 25-pin, two row plug that was normally used to control printers. The use of this port seems to be on its way out in new printers in favor of the USB port.
The pins in a parallel port are numbered from 1 to 25 from right to left starting with the top row.
To see a very good diagram of the pins on a parallel port, check out the following link:
Parallel Port Diagram.
What I want to accomplish with this is to create a bank of eight LEDs where each one is hooked up to one of the eight DATA output pins on a parallel port. Once the curcuit has been built, I want to find or write a simple program that will allow me to turn each of the LEDs on and off.
To make assembly of the circuit easier I am using a solderless breadboard. This way I can simply plug components into it and I don't have to try to solder each peice in place. At this point I do not have much experience soldering so I want to stick to solderless breadboards until I take time to practice soldering.
For the hookup to the parallel port, I removed the parallel port from an old motherboard. Since I do not yet have a desoldering tool, I used my bench grinder to quickly grind the connections loose from the back of the motherboard. This actually worked pretty well, but would not be acceptable if I needed to salvage the motherboard. In the process of removing the port, I did accidently break one of the pins ( pin 1 to be exact ). Fortunately, I will not be needing that pin for this project.
Once removed from the motherboard, the parallel port had very nice long leads that were easy to stick into the breadboard. Here are some pictures of the port installed in the breadboard:
The next task was to find eight LEDs and install them in the breadboard as well. I have quite a large stock of old computers and other electronics that I have saved from the trash over the years. After digging through these, I was able to salvage the eight LEDs. I stuck these into the breadboard in a line, with plenty of space between them, making sure to put all of the positive leads on the same side to simplify the wiring. LEDs will only work one way. If they are wired backwords, they will not illuminate and they will not allow current to pass. Following is a picture of the curcuit with the LEDs installed.
The final step of building the curcuit was to wire it. This too, was fairly simple. I ran one wire from each of the eight DATA pins to the positive side of each of their respective LEDs. I then ran one wire from one of the ground pins to the negative row of the breadboard. This allowed me to simply hook each of the negative leads of the LEDs to the negative row. Here is a wiring diagram that shows how it was wired:
These are some pictures of what the circuit looks like now that it has been completed.
The next phase of the project will be to write the software program to control the LEDs. I should have another entry ready within the next couple of days covering that portion of the project.