Relay card

An 8 relay card for the parallel port. This is a better type, since it has its own buffer, so you can detach the PC after setting/clearing the relays. Most parallel port relay card do not have a buffer, so they are easy to program, just write a value to the data port.

With the TESTLPT program I discovered this card behaves like a printer:
– set the wanted setting on the data pins
– change the strobe output for a short period
– hear the relays click to the requested state

To really test this nice piece of hardware I wrote a barebones program. It can turn on and off each relay, or all relay on and off with one click.
Ofcourse a real application requires a scheduler with programmable activities. Maybe I will add that later, this is enough to test the device and my skills to program it myself.

The LPT Relay program as Windows installable.

The sources of LPT Relay