Parallel port and voltage for project

kodan50 on 26/9/2008 at 04:34

So, I am working on a project that involves me hooking my VMU to my PC. This is for experimental reasons. Here is my problem:

1: The power output of my computer is too strong for my VMU. I am using my parallel port for this adapter. I used a voltage tester on the pins and ran it through ground to determine the computer runs 4.22 volts. Is this a safe and accurate way to properly test my voltage before I go out and purchase the resistor I need to down the voltage to 3 volts?

2: Also, is there any way to also safely draw 3 volts constant power from the parallel port to power my device? The pins I am using are 2, 3, 4, 5, 10, 11, and 13.

Yellow on 26/9/2008 at 06:35

What's a VMU?

That display of ignorance out of the way, it depends on the electrical characteristics of the thing you are connecting to, in particular the current it can safely source and sink. Most parallel ports use TTL signaling (+5V/0V) and can generally sink/source around 12mA.

If the VMU uses 3.3V TTL then you may probably get away with directly hooking the two devices up. If it uses something like 3.3V CMOS you'll have to do a lot more work with active components.

There is a good section covering this type of stuff in "The Art of Electronics" if you can scounge a copy.

kodan50 on 26/9/2008 at 08:49

I'm not sure what the VMU supports as part of its I/O signaling. VMU is a Visual Memory Unit for Dreamcast. I am using a program called VMU2PC and using the pin guide provided for the program. The hardest part though is the voltage output. Between my laptop and my desktop, I keep getting mixed voltage readings, so it looks like I will have to pick a computer and use that one, unless I build my board with swappable resistors.

But, I think the VMU uses more than 12 mA for power consumption, so it doesn't seems like it could utilize the parallel port for power. Wait, is that total, or per pin? I wonder if I could safely draw energy from unused pins, or if that could damage my PC or my VMU somehow. I think I will stick to my AA batteries.