I used the code from
eagerfish to make a simple parallel port control. There's
a BC547 transistor controlling the relay. The LED's are all connected to the parallel
port outputs through a 1K resistor.
This is the basic code I used - it's for linux (I use Ubuntu), there's plenty of windows examples
around though, if that's what you use. I added some code to read a file and output a number
to the parallel port depending on the contents of the file. I'll update the page when it's finished.
I used this code to control this wire forming machine below :
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/io.h>
#include <sys/types.h>
#include <fcntl.h>
#define BASEPORT 0x378 /* lp1 */
int main() {
char c;
int n, tem;
printf("Hit any key to stop\n");
//set permissions to access port
if (ioperm(BASEPORT, 3, 1)) {perror("ioperm"); exit(1);}
tem = fcntl(0, F_GETFL, 0);
fcntl (0, F_SETFL, (tem | O_NDELAY));
//main loop where actual blinking is done
while (1) {
//if some key is pressed, break out from loop
n = read(0, &c, 1);
if (n > 0) break;
//write 'on' bit on all data pins and wait 1/4 second
outb(255, BASEPORT);
usleep(250000);
//write 'off' bit on all data pins and wait 1/4 second
outb(0, BASEPORT);
usleep(250000);
}
fcntl(0, F_SETFL, tem);
outb(0, BASEPORT);
//take away permissions to access port
if (ioperm(BASEPORT, 3, 0)) {perror("ioperm"); exit(1);}
exit(0);
}