The Discordant Opposition Journal Issue 10 - File 17
-- PC Interfacing --
Want to do something new and interesting with that old 486 lying in the corner?
This article will teach you how to control simple electronics with your computer, so you can do things like turn on the lights in your house at a certain time, or even launch bottlerockets! (I'm doing a toaster, for more information on this stupid project, go to http://phaxx.hatrick.ie/etoast)
First, a diagram of the parallel port showing the pins.
_____________________________________________
/ ___________________________________________ \
/ / \ \
\ \13 * * * * + + + + + + + + * 1 / /
\ \ 14 / /
\ \25 0 0 0 0 0 0 0 0 * * * * / /
\ \_____________________________________/ /
\_______________________________________/
Hope my ASCII art is clear enough =)
The pins are numbered one to 25, starting at the top right, going left to pin 13, then starting again from 14 at the bottom right, again going left to pin 25.
-- Explanation of the pin functions --
1 * Strobe
2 + Data line 1
3 + Data line 2
4 + Data line 3
5 + Data line 4
6 + Data line 5
7 + Data line 6
8 + Data line 7
9 + Data line 8
10 * Ack
11 * Busy
12 * Paper Out
13 * Select In
14 * Auto Line Feed
15 * Error
16 * Initialise
17 * Select Out
18-25 0 GND
Right so, you can pretty much ignore pin one, and pins ten through 17, (labeled here with asterisks, '*') as they're used for things I won't cover here.
Pins 18 through 25 are all ground, all connected together. (just so you know, the casing of the connector is also ground, as is the computer's case)
The only pins we need to worry about are two to nine, the eight data lines, and of course pin 25.
Right, with the theory out of the way, on to the first practical!
-- Ooh, lookit the little flashing light! --
IMPORTANT!
Before you start doing anything, it would be a VERY good idea to have a parallel port expension card for the controlling computer, so that if you make a big boo-boo, it won't hurt the computer or it's onboard parallel port. Four of the pins on my linux machine don't work anymore, thanks to my screwing about.
Here, you'll be able to control a little LED. (that's Light Emitting Diode)
For this, you should have the following items
- An LED =)
- A bit of thin-ish wire
- Wirestrippers
- A computer running some form of un*x (for the controlling program, see below for the sources)
- A soldering iron
- Solder
But ideally, you should have one of these thingies in addition to the above;
A 25-pin male parallel port connector (If you're in the USA, it's radioshack number 276-1547)
With that assembled, off we go!
Cut two pieces of wire however long you like, I'd recommend a few inches.
Strip a little bit off the wire, and solder each wire onto one of the LED's pins.
Find out which pin on the LED is negative, and solder it's wire onto pin 25 of the parallel port connector, then solder the positive wire onto pin two of the connector. (that's data line one)
Don't worry if you don't know which pin is which, just try it both ways, you can't do any damage.
Plug it into the parallel port, and then compile the code below with
# g++ ppw.cpp -o ppw
Copy & paste this code into ppw.cpp
(This was written on a Slackware Linux 7.0 system)
*** cut here ***
#include <iostream.h>
#include <stdio.h>
#include <unistd.h>
#include <asm/io.h>
#include <sys/io.h>
#include <string>
#include <fstream.h>
#include <time.h>
#include <ctype.h>
#define BASEPORT 0x378
#define BASEPORT2 0x379
void main(int argc, char *argv[]) {
int total;
total=0;
//Check to make sure all the right information was passed to the program
if (argc <= 8) {
cout << "Parallel port writer\n\nYou cannot give less than ";
cout << "eight arguments!\n(in the format 'ppw x x x x x x x x' ";
cout << "where x=[0,1])\n\n";
return 1;
}
if (argc >= 10) {
cout << "Parallel port writer\n\nYou cannot give more than ";
cout << "eight arguments!\n(in the format 'ppw x x x x x x x x' ";
cout << "where x=[0,1])\n\n";
return 1;
}
//If everything is okay, put together the number to be sent to the parallel
//port
if (strcmp(argv[1],"1") == 0) {total=total+1;};
if (strcmp(argv[2],"1") == 0) {total=total+2;};
if (strcmp(argv[3],"1") == 0) {total=total+4;};
if (strcmp(argv[4],"1") == 0) {total=total+8;};
if (strcmp(argv[5],"1") == 0) {total=total+16;};
if (strcmp(argv[6],"1") == 0) {total=total+32;};
if (strcmp(argv[7],"1") == 0) {total=total+64;};
if (strcmp(argv[8],"1") == 0) {total=total+128;};
ioperm(BASEPORT,3,1); //open the parallel port
outb(total, BASEPORT); //write the number to it
ioperm(BASEPORT,3,0); // close the parallel port
return 0;
}
*** cut here ***
Then execute the code with './ppw 1 0 0 0 0 0 0 0'
What this does is turns on line one, and leaves the other seven off.
As soon as that's run, your LED _should_ have turned on, if not, look here for why it may not have.
The pins on the LED are the wrong way, simply switch the wires over (that's remove the wires, and resolder the one that was on pin 25 to pin 2, and vice versa)
The LED is broken, try another one.
The parallel port isn't working.
The controlling software didn't work, ie, didn't compile or for some other reason - if the problem is here, please let me know.
Well there you have it, your first step in PC interfacing. Oooh. =)
You can easily add more LEDs (I made up eight on a piece of biscuitboard)
If youre doing this, connect all their negative pins together and that to pin 25.
If you want to make the LED(s) flash, here's a snippet of perl that will do the job nicely. Note that it needs ppw to be compiled, and you run it in the same directory as ppw.
(this is all one command, just copy & paste and press return)
# perl -e 'while(){system "./ppw 1 0 0 0 0 0 0 0"; sleep 1; system
"./ppw 0 0 0 0 0 0 0 0"; sleep 1;'
It's all one line, and it makes first turns on the LED, waits a second, turns it off, waits a second, and loops like that.
I'll leave you with that, but I'll be back in the next issue with a guide to launching bottlerockets from your computer! (Set up a cron job to launch one at midnight every night, or launch one in the morning to wake you up!)
phaxx
phaxx.hatrick.ie
root@hatrick.ie
#hackers_ireland, #hackerzlair on DALnet (irc.dal.net)
