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1,2,3,4,5.. LEDs

Discussion in 'LEDs and Optoelectronics' started by mbs, Jan 10, 2015.

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  1. mbs


    Jan 10, 2015
    I'd like to create a circuit with 9 LEDs and light up just one of them.
    Then, after pulsing a switch, having it light one additional LED so that now two are lit. And then after pulsing the switch again, having it light up one additional so that three are lit. And so on until all 9 are lit.

    I'm new to electronics so I'm not sure how to do this and am looking for some advice. I'd like it to be as simple a circuit as possible ideally because that will simplify the actual construction of it down the line.

    At first I thought i needed something like an adafruit trinket and a custom-programmed microcontroller but I've been reading about the 4017 decade counter and was thinking that that might be what I need ( ? )
    But with the counter, I suppose I can envisage different lights lighting up each time, but can't imagine yet how to get an increasing number of lights lit this way.

    Could I ask for your advice please?

    And also.. regarding sending pulses to a counter, do I need a special type of switch for that? If so, is there a name for that type of pulsing switch?

  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    Hi there and welcome to Electronics Point :)

    The CD4017 only activates one output at a time. You can use logic to combine outputs, but a simpler solution is a device called a shift register. The CD4015 is an example. It contains two 4-bit shift registers that can be cascaded to form an 8-bit shift register. If your first LED will always be ON, then an 8-bit shift register is enough.

    To send pulses to the clock input of the shift register, you need a pushbutton that has been debounced. When a pushbutton's contacts connect together, they don't connect cleanly - they generate a burst of noise. Logic ICs are fast enough to respond to this noise, so a single press will cause the IC to advance several steps, sometimes dozens, depending on the type of switch. A debouncing circuit "cleans up" the signal from the pushbutton.

    I designed a similar circuit for someone else, and you can adapt it with only minor changes. See
    Gryd3 likes this.
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