LEDs not displaying byte sent

Discussion in 'The Projects Forum' started by shocking1, Jan 11, 2011.

  1. shocking1

    Thread Starter New Member

    May 10, 2010
    I made a multiplexer (8 channel) from a 74HC4051N. It uses 3 lines (pins 9-11) to select the channel to use on the parallel port (378) to control the mux by sending a byte out on pins 2-9 (the digital data register) to select the channel and wrote a program to do this. The program prints the byte so I believe it is correct. I connected 3 LED anodes one to each pin 2-4 of the port. the cathodes were connected to a 1k resistor to ground.
    I expected the 3 LEDs to to display binary 0-7 but all 3 just glow regardless of the byte sent.
    Should I have connected separate resistors between cathodes and ground? or why do I not get the binary signal sent from the port displayed by those 3 LEDs?
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    Are you sure they are not just switching so fast, they all just appear on?

    How fast are you clocking it?