how do I delay the start of this circuit?

Discussion in 'The Projects Forum' started by Nashuan, Oct 30, 2009.

  1. Nashuan

    Nashuan Thread Starter New Member

    Joined:
    Oct 28, 2009
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    Hey all. I posted this question in the general discussion area, but it may be better suited here. I'm hoping someone can help me with a small project I've been working on, but can't make progress with. I want to make a decade counter that won't turn on for 17.5 seconds. I'm interested in a design like this:

    http://delabs-circuits.com/cirdir/theory/gates/doc00020.html

    I've rigged 10 sets of 7-segment LED displays to show one digit each (each display will show one digit that is alsways the same - no need to encode/decode) and want to have them flash one at a time in place of the LEDs shown in the circuit: staying on for about 1/2 second each. The circuit will be powered by 5V DC and would be activated by a momentary pushbutton switch and I want the sequences to cycle over and over again until the voltage source is removed.

    I contacted the designer of the above-listed circuit and he was kind enough to suggest that I try:
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    "use chip CD4541 for the 17.5 Sec delay

    http://www.standardics.nxp.com/products/hef/datasheet/hef4541b.pdf

    http://www.fairchildsemi.com/ds/CD%2FCD4541BC.pdf

    See the drive circuit here http://www.acroname.com/robotics/info/articles/drivers/drivers.html

    http://terpconnect.umd.edu/~toh/ElectroSim/relay.html "

    ------------------------------------------


    I've purchased the CD4541 chips he mentioned, but am lost in how to hook one up to the circuit and to set the delay I need. Essentially, what I want is to use this circuit in a "geocache", where an audio recording begins and part-way through it, the sequencing of seven-segment displays give you your next set of longitude/latidude coordinates. For those who don't know what geocaching is, imagine a scavenger hunt where the goal is to find a hidden container using a handheld Global Positioning Device (more info is available at geocaching.com). Some of these geocaches have themes and this one will be related to a Boy Scout Merit Badge Series - the Electronic Merit badge. I am pretty new to the electronic scene, so what seems "obvious" to some people may not be to me, though I do have some background to work with.The person I contacted was nice enough to respond and try to help, but I don't want to keep bothering him. Does anyone want to try to help work this out?

    Thanks,

    Nashuan (Michael)
     
    #1
  2. Bernard

    Bernard Senior Member

    Joined:
    Aug 7, 2008
    3,647
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    If you are using 4017, use a second 555 { or one 556 ] as one shot with output,17.5 sec, connected to 4017 enable. Connect a small cap [ .1 ] to pin 2, 10k resistor pin 2 to +V to give a short delayed trigger at turn on. With a high on enable 4017 will be inhibited for 17.5 sec.
     
    #2
  3. Nashuan

    Nashuan Thread Starter New Member

    Joined:
    Oct 28, 2009
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    Thank you Bernard. I'll give it a try. I have a really basic background in electronics, but a fascination with building little circuits. This is a streatch for my 'current' (no pun intended) abilities, but I've been working on it for months and would like to see it actually work for real sometime soon.
     
    #3
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