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Old 14th March 2007, 09:25 PM   #1
cowanrg is offline cowanrg  United States
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Default need help with parallel port interface programming

so, with so many people (myself included) using PC's at the center of their systems, there is a need for more features.

for instance, all my amps turn on and off with 12v triggers. my computer acts as my processor and i have no preamp anymore. i need the computer to somehow control 12v triggers. here is my idea...

a little box that plugs into the parallel port on the computer. it has 5v relays which are simply controlled by the native interface of the port. you would have to get a 12v power supply into the board somehow, but that's as easy as a wall-wart, or you could tap into the computer power supply as well.

now, i was thinking about the whole issue of computers turning on and off creating pops and clicks in soundcards. well, if the amps were controlled with a 12v trigger that was software based, the amps wouldnt be on until the computer and software fully booted, therefore, no pops.

the software would just simple turn on or off the relays. i think it would be best to be command-line based. so you could independantly control 4 triggers. something like: command.exe 1 /off 2 /on 3 /on 4 /off.

so you could have the program loaded for different things (music could only trigger 2 of your amps, surround sound, all of them, etc). and the program could be loaded with your front end software or just on startup.

here is the problem, i have NO idea how to do the software for this. i know enough to know its simple, i just dont know how to go about doing it. the hardware is easy. its just a db-25 connector and a few relays.

anyone interested in helping?
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Old 30th March 2007, 12:48 PM   #2
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Jan Axelson has written an excellent book on parallel port programming -- "Parallel Port Complete" --

Windows 2k, WinXP don't like you fooling around with the ports via the command prompt -- you can have a blast with an old 386 which has BASICA available for free. There are a lot of resources available on the web.

You might be best off getting the little controller from USBMicro --
Click the image to open in full size. this device makes working with the USB bus a breeze. It's less than $40 -- there are some canned programs on the USBMicro website, and you can probably get an inexpensive copy of VB.Net off EBay to customize your application.
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Old 31st March 2007, 05:53 AM   #3
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vb express is free and I dont believe the limitations will affect you (

I would go with USB if possible, but it will obviously be more effort.

Anyway, download VB and play around with it, try out some tutorials, and find some sample code on port control. Enjoy
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Old 31st March 2007, 12:49 PM   #4
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If you sit down with a piece of paper, a pencil and eraser and make a schematic of what you want to do you'll find that VB is pretty easy -- the Microsoft Press books are very helpful -- and the best thing is that they keep track of errors and improvements in the programs -- but there are literally walls of books on programming at any Borders or Barnes&Noble.
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