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monostable triggering

Discussion in 'Electronic Design' started by petrucci, May 23, 2006.

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  1. petrucci

    petrucci Guest

    hi everyone,

    i would want to realize a monostabile with 555 that triggers both with
    a front of slope that of descent of the input. Is it realizable?

    Thanks, bye
     
  2. Fred Bloggs

    Fred Bloggs Guest

    I have this on file- adjust to suit:
    View in a fixed-width font such as Courier.

    ..
    ..
    .. V+
    .. |
    .. +--------+-------+---------------.
    .. | | | |
    .. | | +--------------+ |
    .. [10k] [100k] |rst |[1M]
    .. | | | | |
    .. | | | | |
    .. >-+---||--[10k]-+---||---+-----+trig thesh|--+
    .. | 0.1u | 0.01u | | |
    .. | | .---|out dis|--+
    .. | | | | | |
    .. | | | +--------------+ |
    .. | |/ | |
    .. '--[100k]---| 2n3904 '---------------------|------>
    .. |> |
    .. | ===
    .. | |0.1u
    .. | |
    .. | |
    .. | |
    .. ---------------+--------------------------------+-----
    .. gnd
    ..
    ..
    ..
    ..
     
  3. petrucci

    petrucci Guest

    Fred Bloggs wrote:

    [CUT]
    I'm sorry Fred but i don't know how must adjust it and as it is it
    doesn't function :(
     
  4. Fred Bloggs

    Fred Bloggs Guest

    Well- how would I know how it should be adjusted when you say nothing
    about the signal levels, input timing like input duration and frequency,
    and 555 output pulsewidth?
    I don't know where that circuit came from, but this works better on low
    frequency square waves:
    View in a fixed-width font such as Courier.

    ..
    ..
    .. 5+
    .. |
    .. +--------+-------+---------------.
    .. | | | |
    .. | | +--------------+ |
    .. [10k] [100k] |rst |[1M]
    .. | | | | |
    .. | | | | |
    .. >-+---||--[1k]--+---||---+-----+trig thesh|--+
    .. | 0.1u | 0.01u | | |
    .. | - .---|out dis|--+
    .. | v 1n914 | | | |
    .. | | | +--------------+ |
    .. | |/ | |
    .. '--[10k]----| 2n3904 '---------------------|------>
    .. |> |
    .. | ===
    .. | |0.1u
    .. | |
    .. | |
    .. | |
    .. ---------------+--------------------------------+-----
    .. gnd
    ..
    ..
    ..
    ..
     
  5. petrucci

    petrucci Guest

    Fred Bloggs wrote:

    [CUT]

    i apologize.. so this are some info about circuit:
    input signal level: 5 V and 0 V
    input duration and frequency: random (in the sense that can stay tall a
    second and lower part one minute as tall two minutes low a second...)
    555 output pulsewidth: can be 2 or 3 seconds.
     
  6. Fred Bloggs

    Fred Bloggs Guest

    Okay- the circuit will operate best if driven by HC type of logic. A
    "tall" input will momentarily turn the transistor on which pulls TRIG
    low and triggers one-shot. All of the capacitors are recharged after
    500us, so that when the input goes low the diode couples through the 10n
    to the TRIG causing another trigger. Output pulsewidth is about 2.5
    seconds.:
    View in a fixed-width font such as Courier.

    ..
    ..
    .. 5+
    .. |
    .. +--------+----------+---------------.
    .. | | | |
    .. | | +--------------+ |
    .. [10k] [10k] |rst |[1M]
    .. | | | | |
    .. 1n914 | | | | |
    .. -----|<|---+---||---+--------+trig thesh|--+
    .. | 10n | | | |
    .. | | ---|out dis|--+
    .. | | | | | |
    .. | | | +--------------+ |
    .. | | | |
    .. | | '---------------------|------>
    .. | | |+
    .. | |/ ===
    .. IN >--+-||---[1k]----+---| 2n3904 |2.2u
    .. 10n | |> |
    .. [10k] | |
    .. | | |
    .. ----------------+-----+--------------------------+-----
    .. gnd
    ..
    ..
    ..
    ..
     
  7. Fred Bloggs

    Fred Bloggs Guest

    One last note is that if the input duration is low or high for less time
    than the output pulsewidth, there will be no double pulse. You *have* to
    make the output pulsewidth less than the shortest input duration if you
    want double pulses, otherwise you get just one pulse. There is such a
    thing as fractional seconds- so maybe make the output pulsewidth 1/4
    second- change the 2.2u to 0.22u.
     
  8. petrucci

    petrucci Guest

    Fred Bloggs wrote:

    [CUT]

    i suppose that the 2 nano capacitors are micro.. right?
    however thanks a lot guy!!!!... ah another thing.. if the input signal
    is represented by a switch (so low level is absence of voltage) the
    circuit can function?
     
  9. Fred Bloggs

    Fred Bloggs Guest

    The "n"= nano = 1/1000th micro= "u", so 10n=0.01u.
    No- it won't function very well with a switch for input. You should then
    do something like this:
    View in a fixed-width font such as Courier.

    ..
    ..
    .. 5V--[10k]-+---------------------.
    .. | |
    .. | +----------+ |
    .. | 5V-|rst | |
    .. | | | |
    .. sw | | | |
    .. .-o/o----------+------+trig thesh|---'
    .. | | |
    .. --- .------|out dis|
    .. gnd | | |
    .. | +----------+
    .. |
    .. |
    .. |
    .. |
    .. |
    .. |
    .. | 5+
    .. | |
    .. | +--------+----------+-----------.
    .. | | | | |
    .. | | | +----------+ |
    .. | [10k] [10k] |rst |[1M]
    .. | | | | | |
    .. | | 1n914 | | | |
    .. +--||---+---|<|--+--------+trig thesh|--+
    .. | 10n | | | |
    .. | | ---|out dis|--+
    .. | | | | | |
    .. | | | +----------+ |
    .. | | | |
    .. | | '-----------------|------>
    .. | | |+
    .. | |/ ===
    .. '--||-[1k]-+---| 2n3904 |2.2u
    .. 10n | |> |
    .. [10k] | |
    .. | | |
    .. ------------+-----+----------------------+-----
    .. gnd
    ..
    ..
    ..
     
  10. Fred Bloggs

    Fred Bloggs Guest

    If it's a cheap switch, you should debounce:
    View in a fixed-width font such as Courier.

    ..
    ..
    .. 5V--[10k]-+---------------------.
    .. | |
    .. | +----------+ |
    .. | 5V-|rst | |
    .. | | | |
    .. sw | | | |
    .. .-o/o-[2.2k]---+------+trig thesh|---'
    .. | +| | |
    .. --- === | |
    .. gnd 10u| | |
    .. --- | |
    .. gnd | |
    .. | |
    .. .------|out dis|
    .. | | |
    .. | +----------+
    .. |
    .. | 5+
    .. | |
    .. | +--------+----------+-----------.
    .. | | | | |
    .. | | | +----------+ |
    .. | [10k] [10k] |rst |[1M]
    .. | | | | | |
    .. | | 1n914 | | | |
    .. +--||---+---|<|--+--------+trig thesh|--+
    .. | 10n | | | |
    .. | | ---|out dis|--+
    .. | | | | | |
    .. | | | +----------+ |
    .. | | | |
    .. | | '-----------------|------>
    .. | | |+
    .. | |/ ===
    .. '--||-[1k]-+---| 2n3904 |2.2u
    .. 10n | |> |
    .. [10k] | |
    .. | | |
    .. ------------+-----+----------------------+-----
    .. gnd
    ..
    ..
    ..
     
  11. Fred Bloggs

    Fred Bloggs Guest

    This will give a better debounce:
    View in a fixed-width font such as Courier.

    ..
    .. .-------------------.
    .. sw | |
    .. .-o/o---------------. | +----------+ |
    .. | | | 5V-|rst | |
    .. --- | | | | |
    .. gnd | | | | |
    .. 5V-[1k]-+-[2.2k]-+----+trig thesh|---'
    .. +| | |
    .. === | |
    .. 10u| | |
    .. --- | |
    .. gnd | |
    .. | |
    .. .-------------------|out dis|
    .. | | |
    .. | +----------+
    .. |
    .. |
    .. | 5+
    .. | |
    .. | +--------+----------+-----------.
    .. | | | | |
    .. | | | +----------+ |
    .. | [10k] [10k] |rst |[1M]
    .. | | | | | |
    .. | | 1n914 | | | |
    .. +--||---+---|<|--+--------+trig thesh|--+
    .. | 10n | | | |
    .. | | ---|out dis|--+
    .. | | | | | |
    .. | | | +----------+ |
    .. | | | |
    .. | | '-----------------|------>
    .. | | |+
    .. | |/ ===
    .. '--||-[1k]-+---| 2n3904 |2.2u
    .. 10n | |> |
    .. [10k] | |
    .. | | |
    .. ------------+-----+----------------------+-----
    .. gnd
    ..
    ..
    ..
     
  12. petrucci

    petrucci Guest

    thanks very much Fred!! bye
     
  13. Fred Bloggs

    Fred Bloggs Guest

    If the switch is some kind of power switch then you can do something
    like this:

    View in a fixed-width font such as Courier.



    ..
    .. sw
    .. V+ >------o/o---+---------------------------> Load
    .. |
    .. |
    .. |
    .. .-----[10K]---'
    .. |
    .. |
    .. |
    .. | 5V-[1k]-+-[2.2k]-+-------------------.
    .. | | | |
    .. | | | +----------+ |
    .. | | | 5V-|rst | |
    .. | |/ | | | |
    .. +---------| 2n3904 | | | |
    .. | |> +----+trig thesh|---'
    .. [10k] | +| | |
    .. | --- === | |
    .. --- gnd 10u| | |
    .. gnd --- | |
    .. gnd | |
    .. | |
    .. .-------------------|out dis|
    .. | | |
    .. | +----------+
    .. |
    .. |
    .. | 5+
    .. | |
    .. | +--------+----------+-----------.
    .. | | | | |
    .. | | | +----------+ |
    .. | [10k] [10k] |rst |[1M]
    .. | | | | | |
    .. | | 1n914 | | | |
    .. +--||---+---|<|--+--------+trig thesh|--+
    .. | 10n | | | |
    .. | | ---|out dis|--+
    .. | | | | | |
    .. | | | +----------+ |
    .. | | | |
    .. | | '-----------------|------>
    .. | | |+
    .. | |/ ===
    .. '--||-[1k]-+---| 2n3904 |2.2u
    .. 10n | |> |
    .. [10k] | |
    .. | | |
    .. ------------+-----+----------------------+-----
    .. gnd
    ..
    ..
    ..
     
  14. Fred Bloggs

    Fred Bloggs Guest

    If you use a bipolar 555, the most common ones, to drive the double edge
    trigger circuit, then it will need a bit of an assist on the high-to-low
    transition triggering. Add a 56K resistor as shown.
    View in a fixed-width font such as Courier.

    .. |
    .. | 5+
    .. | |
    .. | +--------+----------+-----------.
    .. | | | | |
    .. | | | +----------+ |
    .. | [10k] [10k] |rst |[1M]
    .. | | | | | |
    .. | | 1n914 | | | |
    .. +--||---+---|<|--+--------+trig thesh|--+
    .. | 10n | | | | |
    .. | | | ---|out dis|--+
    .. | [56k] | | | | |
    .. | | | | +----------+ |
    .. | --- | | |
    .. | gnd | '-----------------|------>
    .. | | |+
    .. | |/ ===
    .. '--||-[1k]-+---| 2n3904 |2.2u
    .. 10n | |> |
    .. [10k] | |
    .. | | |
    .. ------------+-----+----------------------+-----
    .. gnd
    ..
    ..
    ..
     
  15. petrucci

    petrucci Guest

    Fred about input signal piloted by a switch can i simply use a pull-up
    resistor? in this way look:

    +Vcc
    |
    [1k]
    |
    ---/ -+-------IN
    |
    GND
     
  16. Fred Bloggs

    Fred Bloggs Guest

    It will work "most" of the time:

    View in a fixed-width font such as Courier.

    ..
    .. +5
    .. |
    .. .-------+--------+---+--------+---+-------.
    .. | | | | | | |
    .. | | | | +----------+ |
    .. [1k] [10k] [10k] | |rst V+ |[1M]
    .. | | | | | | |
    .. | | 1n914 | | | | |
    .. +--||---+---|<|--+----------+trig thesh|--+
    .. | 10n | | | | | |
    .. | | | | ---|out dis|--+
    .. | [56k] | | | | gnd | |
    .. | | | | | +----------+ |
    .. | --- | | | | |
    .. | gnd | | '-----------------|------>
    .. | 2n3904| | | |+
    .. sw | |/ | | ===
    .. .-o/o-+--||-[1k]-+---| === | |2.2u
    .. | | 10n | |> 0.1u | |
    .. | | [10k] | | | |
    .. | | | | | | |
    .. '-----+----------+-----+---+-----------+--------+-----
    .. gnd
    ..
    ..
    ..
     
  17. petrucci

    petrucci Guest

    what does it mean "most of the time"?!?!?!?!?
     
  18. Fred Bloggs

    Fred Bloggs Guest

    It depends on the nature of the switch bounce. You can simplify things a
    bit by using the bounce like so:
    View in a fixed-width font such as Courier.

    ..
    ..
    .. +5
    .. |
    .. .--------------+-----+--------+---+-------.
    .. | | | | | |
    .. | | | +----------+ |
    .. [1k] [10k] | |rst V+ |[1M]
    .. | | | | | |
    .. | | | | | |
    .. +------. +------------+trig thesh|--+
    .. | | | | | | |
    .. | |10n | | ---|out dis|--+
    .. | === | | | | gnd | |
    .. | | | | | +----------+ |
    .. o [470] | | | | |
    .. sw / | | | '-----------------|------>
    .. o | 2n3904| | | |+
    .. | | |/ | | ===
    .. +-|>|--+-----| === | |2.2u
    .. |1n914 | |> 0.1u | |
    .. | [10k] | | | |
    .. | | | | | |
    .. '------+-------+-----+-----------+--------+-----
    .. gnd
    ..
    ..
    ..
     
  19. Fred Bloggs

    Fred Bloggs Guest

    Along the same lines of relying on switch bounce to trigger the timer,
    this will also work- omits the transistor:
    View in a fixed-width font such as Courier.

    ..
    .. +5
    .. |
    .. .------+---------+-----+--------+---+-------.
    .. | | | | | | |
    .. o [22k] [470] | +----------+ |
    .. sw / | | | |rst V+ |[1M]
    .. o +---|>|---' | | | |
    .. | | 1n914 | | | |
    .. +--||--+----------------------+trig thesh|--+
    .. | 10n | | | |
    .. | | ---|out dis|--+
    .. | | | | gnd | |
    .. | | | +----------+ |
    .. | | | | |
    .. [1k] | '------------------------>
    .. | | | |+
    .. | | | ===
    .. | === | |2.2u
    .. | 0.1u | |
    .. | | | |
    .. | | | |
    .. '----------------------+-----------+--------+-----
    .. gnd
    ..
    ..
    ..
     
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