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PC Parallel port to led

Discussion in 'Microcontrollers, Programming and IoT' started by GaryK4, Apr 25, 2015.

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  1. GaryK4


    Apr 25, 2015
    I am playing with a project to display statuses using the computer parallel port and 5v leds. First let me say that I am a programmer and weak at electronics. I have a number of demo programs that read and write to the parallel port.
    When I put a meter to one of the ground pins and check the (8) data pins, I don't get the expected results. Pins 2-4 (bit 0-2) always have power even when I read the port and it has a zero value. If I set the value to 255, then all of the data bit are on. If I set the value to 128 then pin 5 bit 3 goes on. Using values between 128 - 255, it appears that I can set pins 5-9 (bits 3-7), just not pins 2-4. Any ideas what is happening? Once (if) I get this resolved, I will need help with LEDs and resisters.

    Update: I need to do some more research. It appears that the pins are reversed. Pin 2 is on the top left versus the diagram that I have has it on the top right. Female diagram,male pins.
    Last edited: Apr 25, 2015
  2. Tarjei


    Apr 14, 2015
    Found this diagram while googling this.
    seems like there is only a few of the pins that is able to give 5v.
  3. GaryK4


    Apr 25, 2015
    Yes, I do know that (8) pins have 5v. Electronics is not my thing, but I don't think that all LEDs have the same power specs. I have seen 380 ohms and a guy on You Tube that connected directly to the pins without a resistor. I just don't want to damage my parallel port. I will have spare LED's, so I'm not worried about them.
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