Basic electronic - Parallel port input

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Original post by Hedos Basically, all I want to do is create a small device which contains a few buttons ( maybe 4 to 6 buttons ) and read when the buttons are pressed via the COM port, with an application I would create myself.

I take it you mean the serial port. It'll be a bit complicated to accomplish what you want to do initially because the serial port is designed to take input serially -- one bit at a time. Also, using the serial port is a bit more complex because it is usually accessed with a protocol and IIRC, the voltage levels are quite different from standard TTL 5V logic.

I'd recommend using the parallel port which is essentially a "raw" interface to your computer and is much easier to deal with electrically.

Alright, as I said, I'm a begineer to electronic.
Yes, I was talking about the serial port.
What is a parallel port, I never heard of that, but it looks like it might be what I'm looking for.

edit: The parallel port is the one used for most printers?

For the COM port you probably want to get a RS232 driver ic. Google will give you a few hundred thousand pages worth of info.

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Original post by Hedos Alright, as I said, I'm a begineer to electronic. Yes, I was talking about the serial port. What is a parallel port, I never heard of that, but it looks like it might be what I'm looking for.

The parallel port has 25 lines (DB25 connector) -- many are ground lines. There are 8 data lines (outputs), some control lines, and some status lines usable for input. TTL logic is used where ~0-1V is a logic 0 and 3.5-5V is logic 1.

Over the years the parallel port has evolved to support different protocols for communicating with devices. The standard parallel port mode (SPP) is what you'll want to use initially. The various bi-directional and enchanced modes which allow you to use the 8 data lines as inputs require that a hardware protocol be used (as opposed to implementing one in software.)

The parallel port has 3 programmable 8-bit registers:

BASE_ADDR + 0: Data outputs (D7-D0 lines.)
BASE_ADDR + 1: Status port (used to read in the status lines.)
BASE_ADDR + 2: Control port (control lines and configuration bits.)

The base address will be something like 0x378 -- it depends on your system. It can be obtained from the BIOS data area if you're writing DOS code.

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edit: The parallel port is the one used for most printers?

Yes, it's the printer port.

I'm going to write it for Linux.
Thanks for all these info, it will help me getting started.

Anon Mike: I'll take a look at this RS232 driver, but if the COM port is more complex than the parallel port, I'll certainly go with the parallel port.

Another way is to buy a cheap gamepad and hack the PCB inside so that your buttons make the gamepad send button events. That way you can just use direct input or something similar to read the input.

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Original post by GameCat Another way is to buy a cheap gamepad and hack the PCB inside so that your buttons make the gamepad send button events. That way you can just use direct input or something similar to read the input.

That would be an idea, but I'd prefer to make my own so I can learn and understand what's going on.

A little up, in case someone knowing well the subject would see this.