Repeat Cycle Timer Using Binary Counters

Discussion in 'General Electronics Chat' started by smartyram, Aug 6, 2010.

  1. smartyram

    Thread Starter Member

    Aug 5, 2010
    17
    2
    Hi everybody, I have come up with my own circuit for a repeat cycle timer that switches a motor ON for 1 minute and OFF for 4 minutes and repeats this forever.

    The NAND gate oscillator generates a 1 Hertz clock pulse which is fed to both the counters.

    The first counter counts till 60 pulses (i.e. 60 seconds = 1 minute) and then directs the clock pulses to the second counter. The second counter counts till 240 pulses (i.e. 240 seconds = 4 minutes) and resets both the counters. This causes the first counter to start counting again.

    The relay is activated using the first counter using a relay driver transistor 2N5089TF (with hFE 400). I read on the internet to use a transistor that provides at least 5 times the required current gain (375). The relay draws 75mA and since the NAND gate supplies about 1mA so the required current gain is 5 X (75/1) = 375.

    The circuit will be powered by a 12v sealed lead acid battery to run a 12v water pump.

    I am looking for any comments / suggestions from the experts to improve this circuit. Thank you in advance for your valuable time and inputs.
     
  2. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    I did something similar using a 555 to drive a binary counter. The selected output of the counter representing the amount of off time then triggered a second 555 (actually the other 1/2 of a 556) which was configured as a one-shot. It was set for the duration of the desired on time. Been working for over a year to circulate water in our hot tub. Runs about 10 minutes about every hour. I like your idea better!
     
  3. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    684
    92
    I think you could have two 4541 programmable timers do the same thing.

    I would need to check the datasheets to see why you wouldn't.

    They are cheap too.
     
    Last edited: Aug 6, 2010
  4. smartyram

    Thread Starter Member

    Aug 5, 2010
    17
    2
    Glad you liked it! It is my very first circuit design! :)
     
    Last edited: Aug 7, 2010
  5. smartyram

    Thread Starter Member

    Aug 5, 2010
    17
    2
    These timers divide the clock by fixed counts like 256, 1024, 8192, etc. not sure how I can use them for my one minute (60 pulses) and four minute (240 pulses)?
     
  6. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    684
    92
    You set the frequency to around 275Hz and divide by 65536.
    That will give you about 4 Minutes.

    Rt I would use a 22k Resistor and a 33k trimpot.
    Ct I would use a 25nF.

    The second 4541 is set for around 1100 Hz divide by 65536.
    That will give you about 1 Minute.

    Rt I would use another 22k Resistor and 33k Trimpot.
    Ct I would use a 10nF.

    Look at the logic table and set them up for single cycle and taking turns triggering each other - possibly confusing is you have to set them up to start the other 4541 with the end of each IC's timing cycle, but as long as you are looking out for it there are several ways to do it. Keep in mind that you can set them to pulse low or pulse high depending on if you want them to sink or source.

    What would work as well for your particular timing is to run the first IC as 2 minutes on and 2 minutes off oscillator and have it trigger the mode pin of the 1 minute duration 4541 with that IC set up as a single cycle.
     
  7. smartyram

    Thread Starter Member

    Aug 5, 2010
    17
    2
    Thank you.
     
  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
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    Great job, smartyram!
    You can save a lot of parts if you are willing to change the clock frequency to 1.0667Hz (64/60). See attachment.
    If you want to stick to 1Hz, you can still connect both your decoders to the same counter.
    EDIT: Corrected error in attached schematic.
     
    Last edited: Aug 9, 2010
  9. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Oops! I brought out the wrong pin for the transistor driver. See the edited schematic in my previous post.
     
  10. smartyram

    Thread Starter Member

    Aug 5, 2010
    17
    2
    Ron that was fantastic! I always wanted to get the timer going using only one counter. But never got around to get it working. I was approaching the problem from the front i.e. I started with one minute ON followed by four minutes OFF. Going backwards i.e. four minutes OFF and one minute ON solves the problem elegantly!

    Converting the frequency to 1.0667 gets rid of all that decoding logic. I am down to two ICs from six! Makes is so much simpler to build and test.

    Thank you for showing me the light!
     
  11. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    657
    Excellent! Glad I could help.
     
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