555 timer used for 5 minute delay

Discussion in 'General Electronics Chat' started by Lundwall_Paul, Mar 14, 2012.

  1. Lundwall_Paul

    Thread Starter Member

    Oct 18, 2011
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    I am looking for a 555/556 circuit that runs a 5 minute delay then produces a single 3 second negative pulse (pull-down). Would I use two separate timers and if so how would I interface the two?
     
  2. jimkeith

    Active Member

    Oct 26, 2011
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    How do you want to initiate the 5min timer? Power on? Circuit closure? pulse?
     
  3. Lundwall_Paul

    Thread Starter Member

    Oct 18, 2011
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    Circuit closure
     
  4. russ_hensel

    Well-Known Member

    Jan 11, 2009
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    This will not be easy. It requires a large resistor and capacitor and the leakage of the cap needs to be small. I would use a micro controller ( very often my advice ).
     
  5. Potato Pudding

    Well-Known Member

    Jun 11, 2010
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    If you wanted Astable you could use a 470uF capacitor, with 820kohm and 15kohm resistors.

    If you wanted one shot, then a 556 with 220uF and an 1200kohm resistor triggering to a 4.7uF and 1000k resistor should do it
     
  6. Potato Pudding

    Well-Known Member

    Jun 11, 2010
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    I would suggest counters or a programmable timer.

    The warning Russ gave about the large capacitors needing to be low leakage is important.

    The CD4541 is very useful once you understand the added functionality it offers.
     
  7. KJ6EAD

    Senior Member

    Apr 30, 2011
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    Using a different device as suggested is probably your best option but if you really want to use a 555 or 556 and avoid the capacitor leakage problem, you can use large value ceramic capacitors and multiple timing stages.
     
  8. #12

    Expert

    Nov 30, 2010
    16,257
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    According to the datasheets on capacitors, this can't be done because electrolytic capacitors leak too much. It isn't true. I've done it.

    There is also a CMOS version of the 555 that makes this easier. It has better input specs.
    Warm up that soldering iron and get to experimenting!
     
  9. Lundwall_Paul

    Thread Starter Member

    Oct 18, 2011
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    I was thinking more on the lines of a 5 miniute timer start a 3 second timer on time out of the 5 min.
     
  10. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    A CD4541 has an oscillator and a divider allowing a small reasonable cap to be used to set very long time intervals. You may even be able to get the 3 sec delay out of it too by playing with the output and reset lines.

    The CD4541 is one of those oddball chips that don't quite fit any category but turn out to be damn useful.
     
  11. Wendy

    Moderator

    Mar 24, 2008
    20,765
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    The capacitor leakage problem is overstated in a major sort of way. I have used a 555's for timers that lasted for hours using large caps. You can see what is happening by putting a simple DVM across the cap and watching the voltage over time.

    For an inverted signal such as the OP suggests a transistor will likely also be needed.
     
  12. russ_hensel

    Well-Known Member

    Jan 11, 2009
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    The problem is not just getting the values but getting in the right values and stable over time. As often happens an Arduino is a fairly easy solution that typically gives great accuracy and flexibility. Not very expensive when you consider price per hour of entertainment, in fact for one off projects on all but the leanest budgets is an easy decision to defend. At some point you pretty much have to learn microcontrollers.
     
  13. MrChips

    Moderator

    Oct 2, 2009
    12,421
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    Now is a good time as any to learn how to use a microcontroller.
    You can solve this with a simple 8-pin chip and no other external components.
     
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