how to control a parallel port with labview

[kev 406]

Hi. I'm trying to control a dc motor with a parallel port using labview. the program has to be able to vary the out put voltage of the computer (0 - 5V) through the parallel port into a circuit which will step up the voltage for the motor. Any help would be greatly appreicated. garreth

[Brian_Vibert]

Do you want to output and varying signal from the parallel port pins? If so you can't do it, the port pins are digital and can only be high or low, not inbetween. You can control the individual lines high or low using the In/Out Port vis in Advanced>>Port I/O. For more help on doing this search the message archives (I know I've answered a few) and NI's site, there is some good info on it out there. Try some of these for starters:
http://zone.ni.com/devzone/conceptd.nsf/2d17d611efb58b22862567a9006ffe76/0989d3d9dafae64e8625680400679736?OpenDocument


http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/f4146c66990c46388625695f00726581?OpenDocument


http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/f3c4ee6ee2c23ef386
25646b007882c8?OpenDocument


http://www.advmeas.com/goodies/parallelport.html

I hope this helps get you started
Brian

[kev 406]

hi brian
sorry i didnt make it clear. you are correct by saying that i am trying to control the voltage by setting various pins high or low, i have a vi writen and it seems to run fine but the voltage from the out put pins in the parallel port is too low, 7 out of the 8 pins read 1V and the other reads 3.8v,when they are all set high. what do you think is wrong? garreth

[Aaron Marks]

Are you checking the pin voltages while they are connected to your circuit? The parallel port is TTL, and are not designed to handle any current draw. If your circuit does not have a high enough resistance, then it might be draining power from the pin and causing the voltage to be lower than expected. Check the pins with nothing attached and test them against their own ground pins (18-25 if I remeber correctly). Incidentally, I think the spec for TTL says that anything under .8 is low and anything over 2.2 V is high, so there might not be much you can do about it.

[faisal]

hi, i'm traying to control the parallel port. I just need to use 2 pins to control 2 switches with labview, but i can't find any program in labview that let me do it. please could you help me.
you can send me an email:
faisulin@yahoo.es

thanks