1 second pulse, 30 second delay with repeat

Discussion in 'The Projects Forum' started by Christopher7565, May 14, 2008.

  1. Christopher7565

    Thread Starter New Member

    May 14, 2008
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    Hello. My name is Christopher, and I am with Flathead County Search and Rescue. I am on the K9 team, and one of the problems we face is knowing exactly where our dogs are when we are out in the bush searching for people/victims. We use Garmin Rino radios that have peer to peer GPS polling capabilities. I would like to strap one on our dogs so we can monitor their exact location. The problem is, you can only transmit this info one every 30 seconds (FCC Regulation). So I need to build a timer that will send out a pulse (pos or neg) for one second, every 30 seconds. I was thinking of using a 555 or a 556. All of the info I find is one a continuous pulse output. (Which will not work for this application) Can anyone help me out with the needed components to accomplish this task?

    Thanks so much!
     
  2. nomurphy

    AAC Fanatic!

    Aug 8, 2005
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    Hunters have been using GPS collars on hunting dogs for over a decade, look for a website that handles such devices.
     
  3. Christopher7565

    Thread Starter New Member

    May 14, 2008
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    Yes, you are correct. And they are very expensive. ($400 for the cheapest, and you need a collar for each dog that costs around $20 each) Our unit is all volunteer. So this is money we come up with out of our own pockets.
     
  4. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
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    You probably need both a 555 and a 556 (or three 555's).

    The 555 in one-shot mode for a 1 sec pulse (see monostable operation).

    You'll probably need to cascade the two halves of the 556 to get a pulse every 30 seconds, and trigger the 555 for a 1 sec output.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    See the attached.
    It's a 555 timer with components selected to give a 33-second ON time and a 1-second OFF time. To ensure that you are in compliance with FCC regulations, you should use slightly less than 65K for R2, and slightly more than 2.055 megs for R1.

    Note that there are no bypass capacitors shown between pins 1 and 8. You should use both a 0.1uF ceramic or tantalum and a 10uF electrolytic, as 555 timers make quite a voltage spike when they switch output states.

    Note also that the first "on" cycle will be significantly longer than subsequent cycles, because C1 needs an initial charge time.

    C1 must be pretty accurate; if not, it will throw the timing way off.

    I haven't built this circuit with the components as shown. Your mileage may vary.

    If you need the output OFF for 33 seconds and ON for 1 second instead, get a 2N2222 transistor, and:
    1) Connect the emitter of the transistor to ground.
    2) Connect the output of the 555 (pin 3) to the base of the transistor using a 4.7k Ohm resistor.
    3) Connect the collector of the transistor to Vcc using a 1k Ohm resistor.
    Your 33-second OFF, 1-second ON output will be on the collector of the transistor.
     
    Last edited: May 14, 2008
  6. slegha

    New Member

    Nov 23, 2016
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    I am aware that this is a very old thread...

    I was trying to mess with those 555 timers to get a 1 sec pulse every 30 sec exactly for several purposes... The 555 is not really stable and would not compile as required. I've tried it several setups and the best I was able to have is about 1.3sec pulse every 33 sec time (+/-). The time accuracy of the 555 is terrible. I ended up by using a complicated PLC. The time error is not that big but the manipulation is faster.

    I was also thinking about using a Raspberry Pi. The cost will still logical.

    Regards.
     
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