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Problem with output voltage range... — Parallax Forums

Problem with output voltage range...

gearmonkeygearmonkey Posts: 2
edited 2005-05-07 02:40 in General Discussion
I am attempting to use a sx28 to communicate with a playstation controller (spec here)but I am having this weird problem where the output Voltage range seems to vary based on the average logic value of my output. It works like this, if the output logic level is mostly High the output seems to range from -5VDC upto 0VDC (where logic High equals 0VDC). On the other hand, if the output logic level is mostly low the output range is the standard 0VDC to 5VDC. To further complcate thing if I output a %50 duty cycle square wave, the voltage varies from -2.5 upto 2.5 (2.5 = Vdd/2 in this setup). This is all happening with the 28 plugged into the demo board with the SX Key used to program and run the chip. this happens with or without the playstation controller plugged in so I don't think it has anything to do with that end of the hardware. Does anybody have any ideas about what would cause such an effect and more importantly, what can be done to correct it so that the output always varies from 0 to 5V (vdd).

thanks

Ben

Comments

  • BeanBean Posts: 8,129
    edited 2005-05-06 23:21
    Do you have a common ground connection between the SX and the controller ?
    I don' t know how you would be negative voltage otherwise.
    Bean.

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  • gearmonkeygearmonkey Posts: 2
    edited 2005-05-07 02:35
    Yeah, the playstation controller spec calls has ground and·Vdd sent across the·cable.· That is how the device is powered as well.··There is a power indicator LED on the controller so I know that those lines are working·in some fashion.· I believe that the ground line I am using on the parralax demo board is electrically connected to the SX itself ( I don't think they wouls isolate it)· but since you mentioned it and I agree that it is a resonable source of such problems, I'll check.··
  • Jon WilliamsJon Williams Posts: 6,491
    edited 2005-05-07 02:40
    You should be able to connect to the PSX controller without problems -- I did it with a BASIC Stamp (I gave away my interface board, otherwise I'd have written SX code by now...). Check under out Nuts & Volts columns to find the article.

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    Jon Williams
    Applications Engineer, Parallax
    Dallas, TX· USA
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