# Simple Single Pulse Generator

Discussion in 'General Electronics Discussion' started by Lynx, Mar 15, 2012.

1. ### Lynx

1
0
Mar 15, 2012
A real noob here.
OK - I've had a bit of experience building kits and the like but not designing one.

I want a small simple circuit able to produce a single pulse output of varying duration, independant of trigger length. I've played with using a monostable 555 circuit but getting the trigger pulse short enough is catching me out, without resorting to a signal generator for the clock/trigger which kind of defeats the purpose

Requirements -
1: 12 ish V in, 12 ish V out.
2: Trigger = simple push button switch, non latching
3: Output = SIngle pulse, variable width. What do you reckon the range could be? ideally I want around 100 uS up to 1 Sec. for ease a variable resistor or something would be good but if I need to switch components in and out then so be it. I'm happy to play with different component values to alter the time.

It dosent have to be precise. All I want is a single pulse to go from 0V to 12V once when I press a switch, and not even exactly when I press the switch, a delay there is OK too. I guess a cap discharge could do it but not sure where to start with limiting it. I even thought of using a cap to trigger the 555 but I was concerned I was overly complicating what should be a fairly simple process.

Thanks heaps in advance for any ideas !!!

Lynx.

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,501
2,841
Jan 21, 2010
You need to debounce the switch, then convert the (variable length) pulse you get from that into a very brief pulse, then simply use that to trigger a 555 monostable.

You can actually use another 555 to debounce a switch, and even though it's overkill, it means you're (kinda) building two of the same circuit.

You also may need to do some signal inversion. Google for "non-retriggerable 555 monostable" and you'll probably get something

3. ### Sid723

57
1
Jan 28, 2010
If you have the pushbutton switch trigger a flip flop, then the flip flop will take care of the debouncing. Then feed the output of the flip flop to trigger 555 configured as a one shot circuit with a variable pulse duration.

For this, you may have to add another pushbutton so that you can re-arm (reset) the flip flop.

It all depends on how fast you want to trigger a pulse again and again.