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Question: need two 1-second-pulses 30 seconds after power-on

Discussion in 'Electronic Basics' started by Christoph Ramm, Jan 6, 2004.

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  1. Hello newsgroup!

    Maybe the question is a little confusing, that's why I drew a little

    | ------ ------
    | | | | |
    |-//---------------------- -------- ------//--> output
    | <------- 30s-----><-1s-><-1s-><-1s->
    | <------- T1 -----><-T2-><-T3-><-T4->
    | -----------------------------------------//--> power supply
    | |
    --//--------------------------------------------//--> t

    T1: about 30 s
    T2=T3=T4: about 1 s

    I need a simple circuit, that creates two one-second-signals 30 seconds
    after turning the power on. I tried using the 555 timer IC, but I wasn't
    successfull. Can you help me? Thanks a lot!

    Greets, Christoph

    PS: sorry for that bad english :)
  2. John Fields

    John Fields Guest

  3. not very good, 30 s may be 25..35 s, 1 s may be 0,75..1,25 s
  4. John Fields

    John Fields Guest

  5. Hello John!

    Thank you for your answer. But I have a problem: I can't read the group
    "alt.binaries.schematics.electronic". Maybe you can send the content of
    your answer to my private mail?

    Thank you, Christoph
  6. John Fields

    John Fields Guest

  7. Anand Dhuru

    Anand Dhuru Guest

    You could use a small 8 pin PIC, the software would not be very
    complex. Plus, you could change the pulse durations, nos etc. anytime
    in the future if the requirements change.


    Anand Dhuru
  8. Method 1: 4 x 555 (attached)

    I was pleased to get this working, despite its unimaginative approach.

    Method 2: 4017 (attached)

    This is my preferred approach, as it requires only two simple,
    independent adjustments: the 29.5s mono period and the 1s astable.
    That odd duration of 29.5s was chosen because the clock won't
    necessarily be closely synchronised with the mono outputs. That could
    give rise to an extra delay of up to 1s. Circuit should ensure delay
    between power up and first 1s pulse is between 29.5 and 30.5s,
    'averaging' 30.0s.

    If a slightly inferior output was acceptable, the OR gate could be
    made from a couple of diodes and a resistor, and the half 4001 used to
    make the monostable, eliminating the 555.
  9. Fred Bartoli

    Fred Bartoli Guest

    Hi Terry,
    I'm sure that you can achieve much lower part count (and BTW avoid the 2
    adjustments problem).

    Hint : use only 1x555, 1x74(HC)93.

  10. Hello John,

    thanks a lot, I'll try this!

    Greets, Christoph
  11. Hello Anand,

    I've thought about this solution, it would be the most simple. But I had
    to learn how to program PIS in assembler, I don't know how long this
    would takt. I program C167-uC's in C, I don't know the traps of PICs...

    But thank you anyway!

  12. John Fields

    John Fields Guest

    You're welcome.

    As Terry has suggested, the adjustments might be a little tricky, but an
    easy way to stay out of trouble would be to start with R3 at maximum
    resistance, then adjust R4 (the pot) for the 30s delay from power-on to
    the beginning of the first pulse. After that, adjust R3 until the
    number of output pulses decreases to 2.
  13. fpd

    fpd Guest

    "Fred Bartoli"
    Nice drawings. What application do you use?
  14. "Terry Pinnell" <> a écrit dans le
    Thank you. CircuitMaker.
  15. "Fred Bartoli"
    Never heard any more from you on that Fred...

    I eventually succeeded, but as I said it took a much *higher* part
    count! Here's a breakdown:

    1 x 74LS93 16-state binary counter (didn't have HC type)

    2 x 4001 NOR gates for clock with 2s period and 50% duty cycle

    15 x 4001/4011 gates to detect 3 states 13, 14 and 15 and deliver them
    with appropriate polarities for subsequent logic

    2 x NOR gates to OR states 13, 14 for required 1s output pulses

    2 x NOR gates for bistable used to gate the clock (enabled at PU,
    disabled on final state, 15)

    I had a couple of spare gates left, but in total used 7 ICs.

    So my 4017 approach at
    which uses only 3 ICs remains my recommended solution.
  16. Thank you everybody!

    I decidet to use a cheap PIC, programmable with BASIC. It's the simplest
    application (only few extra parts), simple to program, flexible if I
    need other pulses. Of course, a little overdone... Maybe I'll need
    thousands of circuits some day (and I get rich and famous...), then I'll
    take a look at a simpler, cheaper circuit. In this case, send me your
    bench account, so I'll let you share with my euros :))

    Greetings, Christoph
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