BCD to 7 segment, NO OUTPUT

Discussion in 'The Projects Forum' started by CaptainPrice, Oct 1, 2011.

  1. CaptainPrice

    Thread Starter Active Member

    Aug 12, 2009
    49
    0
    Im using the 74LS47 chip, bought from jameco,
    http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_47790_-1

    I can't get an output on the a-e pins that go to the 7 segment cathode display. The most I get is 0.07 V when low and 0.14 V when suppose to be high. I tried a few combinations with the LT , BI/RIO , RBI pins without getting an output voltage on my voltmeter.
    [testing the chip i have 5v going to Vcc and 0 to ground, inputs A-> D i play with putting from 5v to 0v. I moitor the outputs of pins a-e and get .07 to .14 V]

    (just noticed the output might be open collector, what does that mean for me?)

    Datasheets
    http://www.jameco.com/Jameco/Products/ProdDS/47790TI.pdf
    http://www.jameco.com/Jameco/Products/ProdDS/47790.pdf
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    "Open collector" means that it can sink current, but cannot source current.

    In order to see the output voltage change, you will need to use a resistor between the output and the supply voltage.
     
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