JAuto supports parallel port relay controllers. A "parallel port relay controller" is a device that you plug into your PC parallel port, thereby allowing you control of eight small relays. This device may be for you if your immediate (or long term) needs do not include reading of sensors, or, you simply want to control eight relays in addition to your current solution.

There are various parallel port relay controllers available via the inet; do a Google. I did not go the "already put together route"; I bought a kit (click here).


  • Cheap. $40 with shipping.
  • No additional hw to buy.
  • Uses parallel port, so no cards to install.
  • Switches 8 relays.
  • Easy to assemble.


  • Cheap. You're not going to be running 1K lights off the small relays on this board. They could be used to trigger 12VDC to another (heavy) relay though.
  • Uses parallel port, so once you plug this in you aren't going to be plugging anything else into the parallel port.
  • Switches 8 relays. You can't expand this.
  • You have to assemble it.

As you can see, the suitability of this item depends on your needs and POV. I found assembly to be very easy. I fool around with hardware a lot, but, I almost never have to solder anything. If I can solder this thing up, I'm guessing that most of you can too. Practice on some scrap until you can drop shiny dots.

BTW: The tape in the jpg is to provide scale. It's a standard size DDS4 tape.

Some misc tips for assembling the PC parallel port relay board:

1) Use a 25W soldering iron. You don't want to fry the components.

2) When soldering the components: heat up the PCB solder pad, then lean the iron up to the component leg; wait 2-3 seconds then hit it with the solder; let it sit another 2-3 seconds and remove iron. Don't yank the iron away; remove it gently leaving a "hershey kiss". Helps get a nice joint every time. Use nippy-cutters to clip the kiss-tips off after you're done.

3) Solder components that will be closest to the board first (e.g. resistors, diodes). If you attach a taller component (a LED) before all lower ones are in, it will be difficult to hold lower pieces in place before you solder them. Just use common sense here.

4) The PCB marking for the diodes matches the physical diode markings (heavy band at one end).

5) The LED's have a "flat" side that matches a PCB marking (circle with a vertical line near one side; match 'em up). If by chance you don't get flat-sided LED's, the long leg is the positive leg.

6) The capacitor has a marking showing the negative leg (a fat minus sign); the PCB is marked for the positive leg. Put the (marked) negative leg of the cap into the PCB hole without a polarity sign. Or, put the unmarked cap leg into the PCB hole that is marked "+". Same diff.

7) The transistors will only fit one way.

8) Resistors have no polarity. I always line them up the same way, but it's for aesthetic reasons only.

9) The screw terminal blocks will fit either way; make sure you line them up so the terminal holes face *out* from the board. Pay attention here, I almost soldered one in backwards (you have 9 chances to screw this up).

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