[sci.electronics] How could I make a delayed one-shot?

cyamamot@nunki.usc.edu (Cliff Yamamoto) (08/09/89)

Greetings,

I'd like to thank everyone for their replies on lighting bulbs with TTL.  Now
that I know how to calculate all that stuff, my little circuit is quite happy
(myself included)!

Now I'm trying to whip up something a little different.  What chips would you
use to make a delayed one-shot like this :

normally high input (+12 volts)
-----------+		  ______________	 ______________
	   | goes low	 |		|	|	       |	pulse
(0 volts)  +------------>| .1 to 1 sec. |------>| .5 sec pulse |------> output
			 |______________|	|______________|
			 wait after input	triggering the one
			 goes low before...	shot to generate its pulse

(Note : when the one-shot generates its pulse, the input to the delay circuit
	will go from low back up to high.  The one-shot pulses a solenoid, the
	input is from a microswitch )

I'll probably use a 555 for the one-shot (since it can sink/source 200mA) but
the delay circuit is a different matter.  The timing is not too critical.  I
don't really want to clock any kind of divide-by-n gizmo unless it's all on a
chip or relatively simple to wire.  I'd rather have some simple RC delay and a
multi-turn pot to get some granularity for setting the delay.

Any pointers (especially on any chips that can do this in one package) would be
appreciated.

Thanks again to all you friendly hobbyists!

Cliff Yamamoto

sukenick@ccnysci.UUCP (SYG) (08/12/89)

>use to make a delayed one-shot like this :
>[12 volt pulse that triggers on falling edge: 1st one shot .1 to 1 sec;
> then activates 2nd shot for .5 sec]
>(Note : when the one-shot generates its pulse, the input to the delay circuit
>	will go from low back up to high.  The one-shot pulses a solenoid, the
>	input is from a microswitch )

why not.....take the 12v pulse throgh a resistor to a 5 v zener;
then into a 74LS221 (or 74ls123) dual monostables (and the output
to a transistor to drive the solenoid). You've got one chip
with both timing elements, you can select the type
of edge triggered response (falling or rising)(one has a schmitt trigger
very stable timing without some of the flakeyness of using the
555 as a one shot.