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Parallel Pin Connections

Discussion in 'General Electronics Discussion' started by Bradley Hamspon, Oct 18, 2014.

  1. Bradley Hamspon

    Bradley Hamspon

    3
    2
    Oct 18, 2014
    Hi All,

    First of all I hope that I'm posting this in the correct place, secondly, I'm just getting into electronics from a hobbyist perspective. Whilst I'm not 100% new to electronics there are some things take a few takes to understand.

    A problem has led me to sign up and join in on this forum....

    I am attempting to get connected to a parallel port and the pinouts are shown below:

    [​IMG]

    I have a 24 Volt supply and I have connected up pins 1 and 2, the device I am connecting to powers up just fine.
    The diagram I am reading states that at various times voltage shall pass through the pins 3-4 & 7 -10 for a short period, it states that they are connected via NPN transistors.
    I'm unable to get any thing from the pins, to be honest I'm not 100% sure how to wire the circuit.
    Help would be very much appreciated,
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    Hi Bradley and welcome to Electronics Point :)

    If pins 3, 4, and 7~10 are driven by NPN transistors and are described as active low, most likely they are "open collector" outputs. Inside the device, each output has an NPN transistor with its emitter connected to the 0V rail (pin 1 of the port connector) and its collector connected to the output pin on the port.

    When the device wants to activate an output, it applies current to the base of the transistor, which makes the transistor conduct from its collector to its emitter, like a switch turning ON. The transistor pulls the output pin to 0V. This is the "active low" state.

    When the device is not activating the output, the transistor's collector just floats, hence the name "open collector". You will not measure any voltage on the pin with a multimeter. Measuring just the pin voltage will not give you any solid indication of whether the output is active or not. Google open collector output for more information.

    A quick test is to connect an LED in series with a resistor of about 2.2~3.3 kΩ, between the +24V rail and an output pin. When the output activates, and the transistor pulls the pin down to 0V, this will apply 24V across the LED+resistor combination, which will make current flow, and the LED will light. When the transistor is not conducting, the LED+resistor will pull the output pin up to near the +24V rail voltage, and no current will flow, so the LED won't light.

    You can use any small LED such as these ones from Radio Shack: http://www.radioshack.com/product/i...ce=CAT&znt_medium=RSCOM&znt_content=CT2032233 (green) and http://www.radioshack.com/product/i...ce=CAT&znt_medium=RSCOM&znt_content=CT2032233 (red). A suitable resistor is http://www.radioshack.com/product/index.jsp?productId=2062326.

    Connect the anode (the longer lead) of the LED to the +24V supply. Connect the other lead of the LED to one end of the resistor. Connect the other end of the resistor to the output pin. The LED should be illuminated while the output is active.

    I suggested Radio Shack because I assume you're in the U.S. If not, please put your location in your profile. Actually, please do that anyway!
     
  3. Bradley Hamspon

    Bradley Hamspon

    3
    2
    Oct 18, 2014
    Thanks Kris, I'll update my information in the next few minutes. Thanks for sharing your knowledge withe me.
    I've been reading through many other posts and can see that your a big contributor to the form - keep up the good work :)

    Thanks once more.
     
    KrisBlueNZ likes this.
  4. Bradley Hamspon

    Bradley Hamspon

    3
    2
    Oct 18, 2014
    Well I feel like a complete numpty for not being able to work that out myself but I just did as you said and surprise - it worked. Thanks a bunch, I'll be sure to try and assist on the forum - not sure what good I'll be though!!
     
    KrisBlueNZ likes this.
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
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