monostable triggering

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 . . . .

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 . . . .

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...)

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

. . . 5+ . | . +--------+----------+---------------. . | | | | . | | +--------------+ | . [10k] [10k] |rst |[1M] . | | | | | . 1n914 | | | | | . -----|

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.

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?

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 | | | | . +--||---+---| | . [10k] | | . | | | . ------------+-----+----------------------+----- . gnd . . .

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 | | | | . +--||---+---| | . [10k] | | . | | | . ------------+-----+----------------------+----- . gnd . . .

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 | | | | . +--||---+---| | . [10k] | | . | | | . ------------+-----+----------------------+----- . gnd . . .

thanks very much Fred!! bye

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 | | | | . +--||---+---| | . [10k] | | . | | | . ------------+-----+----------------------+----- . gnd . . .

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 | | | | . +--||---+---| | . [10k] | | . | | | . ------------+-----+----------------------+----- . gnd . . .

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

It will work "most" of the time:

View in a fixed-width font such as Courier.

. . +5 . | . .-------+--------+---+--------+---+-------. . | | | | | | | . | | | | +----------+ | . [1k] [10k] [10k] | |rst V+ |[1M] . | | | | | | | . | | 1n914 | | | | | . +--||---+---|

what does it mean "most of the time"?!?!?!?!?

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 . . .

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 . . .