Sending current through a parallel port

[DemonMade]

Ok here is the scenario. Say you have an AA battery running to a switch then to an LED then back to the battery. Simple stuff. What I want to do is replace the switch with a computer. Run from a power source into a parallel (or serial) port, then back out to a device (LED) so when the user clicks a button on the screen, the corresponding LED turns on.

Dose anyone have any experience with this type of thing? ANY help at all would be appreciated.

DemonMade

[gigemboy]

I dont think so, It is my understanding that only data can be sent through parallel cables, no power. I would think you would need some kind of chip or circuitry in the switch to interpret the data, then seperate circuity to turn the switch on and off... then again... I only had a couple electronics classes back in the day, and failed miserably before I switched from being an engineer to an official computer nerd

EDIT - The more I think about it, the more I am moved to think you can't do it. Take printers, for instance. If you would be able to do that, I would think that you would have more printers having some sort of "shutdown" option in order for you to turn your printer off from your computer, yet, I haven't seen a printer yet that can do that (of course, I am not around printers that often... just the ones I use..)

[wossname]

I think you can draw a maximum of 5 volts from the LPT port. Not sure about the amperage. You can easily run 8 LEDS simultaneously. I once made a gadget that displayed the parallel ports line status by linking an LED to each of the data pins. Do a search on VBF, someone else did it a couple of months ago.

You can easily damage the motherboard if you don't know what you are doing though, so be warned.

[campster]

Not sure about the current drain available on the parallel port but you can give this a shot. Tie the anode of the LED to one bit on the port and the cathode to another. You will need to provide a current limiting resistor so that you do not destroy the LED. Within your code, hold both bits either high or low to turn the LED off and toggle one or the other to turn the LED on.

I have no clue how to control the parallel port via VB though.

[DemonMade]

I guess to clarify I don’t NEED power to be moved through the port, but the computer NEEDS to be the switch somehow. I’m looking at streams to see if that is the rout to take...

[Shaggy Hiker]

Search the ClassicVB forum, and the hardware forum. There was a fairly lengthy thread on this subject a few months or a year ago. The one thing I remember clearly was that somebody said that you should go to some second-hand computer place to get a test computer for working on this kind of thing, because the chance of doing major damage was significant.

[DanielS1324]

Dont try to use the parallel port as the current source, your just asking to burn it out if you do that.

Use the port to control a transistor, which will in turn switch the LED on and off.