Simple Computer->Relay Controlled Light Circuits

Thread Starter


Joined Nov 1, 2007
Hey, I'd just like to preface the description of my idea for a project with this statement: I am very new to circuitry. I would also like to say that I LOVE a challenging project and am very eager to learn whatever I need to in order to build my idea. I've started reading the tutorials on the homepage of this website, started being the keyword.

Moving on, here is exactly what I'm trying to do:

I've had the idea of making a series of computer controlled strobe lights or other types of lights that one would find at a party for about two weeks now. I've known that I can easily do the programming for such a project, but the actual hardware aspect is currently beyond me (My high school offers nothing in the way of electronics courses or even an adequate programming course, so I'm left to learn everything on my own).

After seeing an article on Digg entitled "How to make a computer controlled light show for less than 40$" ( I thought to myself, "Wow, I would love to do that!" So, I read the steps of the project and thought that it was all very doable and that the programming won't be a problem at all. That is, until I realized that the relay board that the author of the article used was controlled by a parallel port. My problem is that house only has Apple computers which have no parallel ports.

I then began to search for USB controlled relays, but I don't really know what I am looking at. I do know that I would like to have the ability to turn on and off a series of 120 volt strobe lights within a split second based on messages sent from a computer to a controller board. Ideally I would like to be able to have 8 individually controllable relays which I can turn on and off at least 20 times per second (If that is possible!).

Any suggestions, links, or step by step tutorials with images would be awesome!


Joined Jul 10, 2007
Mostly I just browse this website with nothing to say, but every now and then, something comes up that I have a hint of a clue about. This happens to be something that I have done a tiny bit of.
I was given a parallel port relay card very similar to yours- I wrote my program in Visual Basic and used a 3rd party dll file to do the hard part, then when it came to the sequencing couldn't be bothered working out any simple databases to go with it. Ultimately, I wrote it in Microsoft Excel 03 VBA (a slightly cut down version of visual basic built into the excel file). I put my sequencing into the excel table, which the macro then read and sent to the card via the 3rd party dll.

1: parallel port is very easy to program.

2: USB is very hard to program and/or decode to the relays (to the best of my very limited knowledge)

3: I know you can get USB to serial port converters out there. I have seen them, in the odd electronics shops for ~$20AUD. I have just found a USB to parallel port converters online though. Not hugely common. You want the DB25 parallel, not the 36 pin centronics printer parallel. Here is a link to a site to get one for $9.99 (AUD??)

4: You can get kits that do the same thing as the parallel port cards with serial.

I have had a look at the serial port communications, and I think it would be impossible to directly convert a serial port signal to a parallel port one. Serial only seems to have 3 outputs, and they don't work the same way as parallel.

So: I can help you a little if you use parallel port or a converting lead. If you get a serial port kit of the same relay output device, and use a USB to Serial cable (or have a serial port on your machine), then that may work as well.
For $59AUD, Altronics have a suitable serial kit, but you will need to stick your own relays in (not hard).

So basically, get the $9.99 adapter cable and then do whatever you would otherwise do with an ordinary back of machine parallel port. Including attach a really old printer.
And I hope it works on Mac!! :confused:



Joined Mar 8, 2007
I could not find any parallel port card for the Apple in the links provided.
Many of the projects with parallel ports work differently from the way the parallel ports work with the printer. And, this means, that a converter (from USB or Serial) most likely may not work with the project, as the converter is meant to transmit the data to the printer.
Better option is to look for a serial port relays, if available (and, if your Apple supports it!)