3 pulse generator

Discussion in 'General Electronics Chat' started by Gus_452000, Aug 26, 2011.

  1. Gus_452000

    Thread Starter New Member

    Aug 26, 2011
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    Hi all,
    just wondering if anyone can help me, I am looking for a nice simple circuit, that will allow for example, a simple push to make switch contact produce 3 pulses, that is one contact will produce a stream of 3 contacts.

    Sorry not explaining this very well, but I wish to use this device to connect 2 different amateur radio's together and have a one control that will allow me to control both radios togther, correcting for doppler. The first radio is on 145mhz and the second is on 435mhz ( the doppler will be 3 times as great on the 435mhz radio as on the 145mhz radio). So the circuit will need to allow me to produce 3 pulses in a stream so that the radio is correct correctly for doppler.

    I sure hope someone understand what I am chatting on about, I really just want a very simple circuit that will for a single imput produce a series of 3 contacts maybe .25 - .5 seconds apart.

    regards

    Angus M0IKB
     
  2. iONic

    AAC Fanatic!

    Nov 16, 2007
    1,420
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    Something like this?

    [​IMG]

    If yes, then we need to know what the amplitude of the pulse is? 1V, 5V, 20V??
    And the pulse duration? .1s, .5s, 1s, 2s...?
     
    Last edited: Aug 26, 2011
  3. SgtWookie

    Expert

    Jul 17, 2007
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    What kind of current/voltage do you need to supply with these three contacts?
    [eta]
    The attached is one way to do it. When power is applied, the counter clocks the 4017, and it outputs 3 pulses to the optocoupler (which you can use as an isolated, low-current switch) and then Q2 causes the 555 reset pin to be pulled low.

    Breaking the connection between Q2's collector and the 10k pull-up resistor R5, or momentarily pulling the 4017's MR pin high will start the cycle again.
     
    Last edited: Aug 26, 2011
  4. Gus_452000

    Thread Starter New Member

    Aug 26, 2011
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    Wow thanks for the information guys, very helpful, well to be honest I think SgtWookie, has done the business for me.

    I want to close one switch, which will change the frequency on one radio by 10hz and on the other radio (3x) 30hz, the radios are old Yaesu FT480r and FT780r, and have a simple set of buttons on the fist mic for UP and DOWN freq. control, hence my idea of switching the 145mhz radio and the 435mhz being corrected at the same time, but by 3 x the freq. difference.

    But being old radios and really still in first class condition, I dont want to damage the radios and so decided a simple interface between the UP/DOWN controls on each radio would do the trick. The opto isolated output is rather clever, but may not be needed (if I am wrong please let me know). But I do like that idea SgtWookie

    regards
    Gus M0IKB
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    The optoisolator can only source/sink about 8mA current. I don't know how much current you might need, but it probably is not much.

    Optoisolators will provide a great deal of isolation between your radios and the circuit. More importantly, they are not subject to "contact bounce" like relays and mechanical switches would exhibit. They are also very cheap, likely under $2/each.
     
  6. Gus_452000

    Thread Starter New Member

    Aug 26, 2011
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    Hi,
    once again very many thanks for all the information, have most of the bits needed in my "junk" box, but is it possible to speed up or slow down the pulse rate (this is all trial and error stuff) and I am not 100% sure of how fast or slow I need the pulses?

    regards
    Gus M0IKB
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    I used 1uF for the timing cap C1 because it is a pretty standard value that most people would have.

    Decreasing C1 will decrease the time.

    Decreasing R1 will also decrease the time. It will be easier to change R1. You might consider instead of using a fixed R1 to use a fixed 100k resistor in series with a 200k pot. That way, you will have an adjustment range of roughly 3 pulses in 2.7 seconds to 3 pulses in under 1 second.
     
  8. Gus_452000

    Thread Starter New Member

    Aug 26, 2011
    4
    0
    Hi,
    just one last question in the circuit diagram there is I think a resistor between the 3 dioides and the transistor, what value should this be?
    many thanks again for all the help
    Gus M0IKB
     
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