Parallel Port Interface Circuit

One of the earliest interfaces to a computer I made was 8 LEDs connected to the parallel port. I wrote a quick QBasic program to do all sorts of patterns like chasing lights, count up or down in binary, alternate flashes, etc. While it wasn't the greatest thing in the world it helped me learn a lot about the parallel port and of course programming.

Today I sat down and gave the full set a programs a run through by making a buffered parallel LED interface. I have posted the schematic for all to take a look at.

http://geeksinside.com/files/CIRCUITS/images/parallel_simple.png

A little explanation for those who are new to hardware. The DB25 connects through two 78244 octal buffers to 12 LEDs, 8 for the data port (pins 2-9) and 4 LEDs for the control port (Pins 1, 14, 16, 17). The buffers are there so you don't fry your parallel port. There is also a 10 pin DIP switch to set the input pins of the status port (Pins 15,13-10). This is a simple setup that anyone can build to get started with hardware. I posted the schematic image and the image from PCB after I exported it, ran sch2pcb, auto routed and squished it down (the PCB image isn't very clear)

To learn more about there parallel port take a look at these URLs. Enjoy!

http://www.geocities.com/nozomsite/parallel.htm
http://www.doc.ic.ac.uk/~ih/doc/par/

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