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4015 shift register

Discussion in 'General Electronics Discussion' started by martyn, Jul 14, 2011.

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  1. martyn


    Jul 14, 2011
    having made my 4015 dual 4 bit shift register act as a ring counter, the problem i have now and need to solve so i can multiplex my led array,is ,how do i make only one output active at a time. ive tried all sorts of AND, NAND ,SR flip flops in all sorts of combinations,making, some very nice patterns but just cant get only led on at time and look like its a chase.
    i cant use a 4017 and this chip in cascade mode acts as a divide by 10 functions.
    i need to have one output for 100 leds.
    can any one help?
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    The problem with using a shift register like this is that you need to ensure that there's only a single '1' bit circulating through it.

    Once you have more than that, there is no way to have just 1 LED illuminated.

    The simple solution is to use a small PIC (or PICaxe) to control the reset, clock, and to inject the first '1' bit into the loop.

    The programming is trivial, you just have to be a little tricky with how you connect the ring so that the PIC can override the bit fed back from the other end of the loop. A couple of diodes and a resistor could do it, but with a little programming magic, you *could* do it with a single resistor.

    Did you mean :D? place a : then a D and it will appear. :)
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