Oh you're still here? Good! In this article I'd like to present a project where I did just that. Now I should say right up front that you can just buy these things and they're called Break Out Boards (BOB) and one will set you back anywhere from $25 to say maybe $50 or more depending on the features, or how greedy the seller is etc. My board cost me about $6 to make but I had some of the most expensive components on hand to work with. Namely the barrier terminal strips, which if you're creative you don't even really have to use.
These boards aren't much more than glorified terminal strips anyways but we'll be addressing just exactly what is going on here throughout the article. These are the features of this project:
- Low port micro-ampere current draw
- Reliable known output source or sink current of 24ma
- Simple connection
- Easy construction
OK now I know that doesn't sound like much and it really isn't but that isn't to say that this is trivial or unimportant either. I thought long and hard about the mysteries of the Parallel Port before I built mine and what this board primarily does is remove a lot of the unknowns from the interface. Unknowns such as just how much current can I draw from a Parallel Port? Go out and search I dare you to get a straight answer. Come back when you're as confused as I was and we'll talk about it.
Hook my board up and it is a cut and dried 24ma. If you draw more you're probably only out a 50 cent IC too. That alone HAS to be worth the price of admission! But wait there's more, it slices, it dices, it julians fries ... OK maybe it doesn't do those things. What it does do though is plug into a parallel port and give you convenient buffered connection points.
Like I said they sell these things commercially so it can't be that stupid. It really isn't either.
Step 1: About the Parallel Port
I know today's computers no longer come with parallel ports but that isn't necessarily such a bad thing. First off who wants to put a valuable new computer at risk experimenting on it? I know I don't! Second parallel port cards are still available that will plug into any machine with a PCI slot. These add on cards offer several advantages over a built in parallel port as well so they are worth considering if you plan on trying this project for yourself. An add on Parallel Port Card is what I use. USB to parallel port adapters are outside the scope of this project so I won't be addressing those at all. My board will likely work with those as well within the limits of the USB specification. If you don't know what that means search for USB realtime to see if it applies to you.
The advantages of an add on card include the fact that the add on board isn't built into your PC, so there is less risk of damaging the motherboard connecting to one. These cards are far cheaper than motherboards so if you break one you are out a lot less. Also, the add on boards are often more robust than many built in parallel ports are, so a port card is a bit harder to break to begin with. Now if you have an old PC hanging around and you don't care too much if you break it fooling around then using that is fine too. Old PCs can be cheaper than cheap, free even. While add on parallel ports cards are pretty cheap they're not cheaper than free.
The whole point of this project is really not to break anything at all though. The point being that while yes it is fun to play around with stuff, it is less fun to play around with stuff and break it. The hardware discussed in this project is meant to shield and protect a PC from your external tinkering. Now I cannot guarantee that you still won't break something if you try this. But I can say that if you build this project right you will be able to do a bit more than you normally can with just a plain old parallel port.