Decade counter

Discussion in 'The Projects Forum' started by gonks, May 17, 2012.

  1. gonks

    Thread Starter New Member

    Nov 4, 2011
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    0
    I am trying to create a circuit that when turned on will illuminate between 6 and ten Led's and then on an input from a 555 it will turn them off in sequence. It is to simulate a charge going down over time in a sci fi prop. I would like each light to go out after a gap of about 3-5 minutes.

    Any suggestions would be useful.

    Cheers

    Neil
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,093
    3,031
    This is a bargraph-type display, right? And you want a linear (with time) decay, for instance one of ten LEDs goes out every 30 seconds for 5 minutes?

    Should be easy, I just wanted to clarify the goals for the pros here.
     
  3. gonks

    Thread Starter New Member

    Nov 4, 2011
    4
    0
    Yes that's exactly the idea.
     
  4. gonks

    Thread Starter New Member

    Nov 4, 2011
    4
    0
    Sorry I just read your post there and thought I would clarify a bit further. I want the following to happen.

    1. Turn the power on and all ten LED's on a bargraph illuminate.
    2. After a preset time (1-5minutes) the first LED will go out leaving the rest on.
    3. After another 1-5 minutes the second led will go out leaving the rest on.
    4. so on and so forth this cycle continues until all the led's have gone out, then the circuit needs to be reset manually before the cycle starts again.

    Hope this helps to describe the logic.

    I would also prefer to do this without microcontrollers.
     
  5. gonks

    Thread Starter New Member

    Nov 4, 2011
    4
    0
    I think I have made some progress using a 74hc164 and a 555 to charge the lights, then another 555 set up to trigger the register to turn each led off in turn. I'd probably use a 556 for ease of fitting it into a small unit. Once I get the timings right in a simualtor I'll post my schematic for comments.
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,093
    3,031
    Excellent plan.
     
  7. crutschow

    Expert

    Mar 14, 2008
    12,991
    3,226
    I don't understand the reason for the first 555. Just use a power-on-reset circuit (resistor to V+ and capacitor to ground) to reset the register to all zeros, then use one 555 to trigger the register to turn off the lights, one at a time.

    You connect the positive terminal of the LEDs to the V+ and the negative terminal to each register output (through an appropriate resistor) so that an output zero turns the LED on. If you need more than 8mA through the LED you can add a PNP buffer.
     
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