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Low frequency timer / flasher

  1. Nov 12, 2012 #1
    I want to build a low frequency, uneven cycle flasher somewhere around 10 seconds on, 5 seconds off. I planned on using a 555 timer and a MOSFET to drive my load, a small DC motor. Are there any other suggestions for something at low frequency? I'm just concerned at the R and C values needed for such low frequency as I might be able to buy a cheaper timer already assembled.

    Thanks.
     
  2. jcsd
  3. Nov 13, 2012 #2

    Bobbywhy

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    Gold Member

    Do you expect that since you need such timing control for your 555 that "the R and C values needed" will be expensive? What is the cost of one resistor and one capacitor combined?

    A cheaper timer might be constructed by placing a gerbil on a rotary treadmill. You could mount a contactor near the circumference to energise a microswitch each revolution. You'd need to teach the gerbil the correct timing, and also feed him or her, so it might be cheaper to stick with the 555 timer.

    Cheers,
    Bobbywhy
     
  4. Nov 13, 2012 #3
    I believe what bobbywhy is saying, is that one R and C probably aren't going to cost you that much.

    Use Mouser.com to find some L and C with $ values.
    http://www.mouser.com/Passive-Components/Capacitors/_/N-5g7r/ [Broken]
    http://www.mouser.com/Passive-Components/Inductors/_/N-5gb4/ [Broken]


    Also, you could try using an oscillator. I would suggest a Wien bridge oscillator.
    http://en.wikipedia.org/wiki/Wien_bridge_oscillator

    That way, you would buy 2 R and 2C instead of one C and one L

    You would have to change the duty cycle of the Wien Bridge oscillator. Im trying to find the circuit for that....
     
    Last edited by a moderator: May 6, 2017
  5. Nov 13, 2012 #4
    Well, I didn't think they would, but I think the original documentation and formulas I had misled me. Originally, I looked at the calculations and thought that even with R values in the 100 kohm ranges I would need very large $5+ capacitors to make the high time what I needed. I see now that even with 7.5k and a 1mF cap I'll be in the range I need.
     
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