555 timer delay

Discussion in 'The Projects Forum' started by Didgitalpunk, Sep 5, 2014.

  1. Didgitalpunk

    Thread Starter New Member

    Sep 5, 2014
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    Hello, I'm new to this forum so I'd like to do a quick presentation of my motifs for being here.
    I'm a 19 year old student interested in electronics since a couple years. I also practice airsoft, which drives most of my circuit building (for making props among other things).

    So, a couple days ago I started on a project of making a bomb prop for my airsoft team. I got the beeping all figured out (555 multivibrator with diode taken from here ).
    Now all I need is a timer to turn te bomb on at the start of the game (by means of pressing a button) and have the output of said timer turn on or off after a preset amount of time (planning on having 5-15-30-45 minute presets from which you can choose).
    I found this page while looking for such a diagram, but unfortunately, it doesn't work for me, and the page is written in an unknown language which resemble chinglish (that Chinese-English mix we have on our gun's manuals)
    it is pretty much exactly what I want, except the delays are not correct for me, and there is no formula given to calculate the delay...
    And so I come here asking for help! does anyone know how to fix the diagram I found on there and know the formula to calculate R2-3-4-5?
     
  2. wayneh

    Expert

    Sep 9, 2010
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    The timing of a 555 monostable (one shot) timer is set by the timing components, the R and the C, and you can find many calculators to help you choose values, as well as the formula those calculators use if you want to make your own in Excel for instance. 45 minutes is quite long for a 555 - you'll need a big capacitor and a high ohms resistor.
     
  3. wayneh

    Expert

    Sep 9, 2010
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    Do you mean that you tried the circuit and it didn't work?

    Which 555 are you using? And the capacitor? Things like leakage from the capacitor can be a problem with very long times. There are work-arounds.
     
  4. Didgitalpunk

    Thread Starter New Member

    Sep 5, 2014
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    I tried this circuit with an NE555N, and an electrolytic cap for C2
     
  5. wayneh

    Expert

    Sep 9, 2010
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    And what happened? Did you watch the voltage on C2 (the big cap)? It should gradually rise until the 555 triggers. Were you using a 9V battery as shown?

    Try using a smaller value resistor to speed up your testing, so that you get a timing of just a few seconds or so. This will allow faster tests. If that works, then you know you may have a leakage problem.
     
  6. Didgitalpunk

    Thread Starter New Member

    Sep 5, 2014
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    I tried this circuit with an NE555N, and an electrolitic cap for C2
    I didn't watch the value rise, but I did try using a smaller value resistor, and nothing happened. I was using a 9v battery.The buzzer goes off as long as the button is pressed, but nothing happens after you realease it. Going to keep looking for monostable circuits calculators
     
  7. wayneh

    Expert

    Sep 9, 2010
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    Trying tying pin 4 (reset) to Vcc. That seems more commonly used in one-shot circuits than the arrangement you used. Take a look here, for instance.
     
  8. Didgitalpunk

    Thread Starter New Member

    Sep 5, 2014
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    haha, well, I was looking in the right direction! Found the same page as you. didn't see your reply right away, was actually making that circuit on a proto-board. trying it out right now.
     
  9. Didgitalpunk

    Thread Starter New Member

    Sep 5, 2014
    5
    0
    Yup! Tis working wonderfully! Thanks for the help Wayneh :D
     
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