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

    Oct 28, 2009
    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:

    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:
    "use chip CD4541 for the 17.5 Sec delay

    See the drive circuit here "


    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 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?


    Nashuan (Michael)
  2. Bernard

    Bernard Senior Member

    Aug 7, 2008
    Tucson AZ USA
    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.
  3. Nashuan

    Nashuan Thread Starter New Member

    Oct 28, 2009
    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.
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