pull up resistors on parallel port?

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26 Oct 2010 18:38 #4881 by jtbarclay
I'm just messing with motors and my driver boards and getting everything running with emc before I build any hardware,

I'm using easydriver v3 boards. The problem is the 1.7v signal from my parallel port isn't enough to set the direction pin high. Just messing around I put in a 100ohm resistor between the dir pin and v+ (12v for my motors) and both directions worked. Although it got very hot, running 1.44W through a 1/4W resistor usually doesn't end up working. So I tried 100k and then a 10k resistor, neither worked.

I need to go home and search for a 1k resistor still. What is the maximum current I can sink through the low parallel pin? Or is this a bad solution, does anyone have a recommendation?

Thanks,
Jon

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26 Oct 2010 19:47 - 26 Oct 2010 19:51 #4885 by andypugh
They will normally sink about 15mA, but some will only source 3mA.
1.7V seems broken, is it that low with nothing connected?

I would be more inclined to pull up to 5V (you can source 5V with the same 0V reference from a USB socket)

What is it connected to? It the inputs are opto-isolators then they might work best with +5V to the + of the Opto, and your P-Port connected to the -ve side. That is certainly the way my drives expect to be connected, and they include the right resistor to make that work.
Last edit: 26 Oct 2010 19:51 by andypugh.

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27 Oct 2010 22:55 - 31 Oct 2010 01:29 #4916 by jtbarclay
Opto isolator! Thank you, I don't know why I didn't think of that before. Currently I just have the drivers connected directly to the p-port.

edit: searched my 'tronix stash and found a tube with 39 4n36's inside. Will make new post with my circuit.
Last edit: 31 Oct 2010 01:29 by jtbarclay.

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