AW: dumbass 555 timer question

[Haible Juergen]

	>I need to build something with parts I have on hand.  What I need
is a
	>device that goes from a short trigger pulse to a long footpedal
stomp.
	>
	>I'm thinking of using a 555 timer in monostable mode.  I'm guessing
I will
	>need a transistor going in to convert the trigger into a negative
going
	>pulse and then another transistor to take the positive pulse out to
short
	>the footpedal input to ground.
	>
	>Since I'll have to solder this point-to-point is there a more
elegant way
	>to do this to avoid inverting both sides??


I'd do this exactly as you described it. Two additional transistors cost
next to nothing.

Anyway, if you *really* want to go minimum part count, you might try a
single transistor solution (no 555):

The emitter goes directly  to gnd. 
The base goes to your input pulse by a resistor Rb
The collector goes to +9V by another resistor Rc,
and to gnd by a capacitor C,
and also to your footpedal switch input.

The idea is that a short pulse will cause the transistor to discharge
the capacitor very fast, and it will only slowly be charged again thru
Rc, so the pulse is prolonged and inverted. (and misshaped)

Just a simple gate to switch trigger circuit with the output bypassed 
by a capacitor.

BUT this will only work if:
* the footpedal switch input has high impedance
* the footpedal switch input has some schmitt trigger or at least
  comparator input circuitry.
You may be lucky and these conditions are fullfilled; then you might find
a combination of Rc and C to get the desired result. (Rb should be
approx. 10k for a start, Rc should be smaller than the footswitch input
impedance, and (Rc * C) should be close to the desired output pulse time.

Hey, I do *not* recommend this as a general diy interface, but it may
actually
work in a specific configuration, and you asked for an elegant, low parts
count solution ... so don't sue me. (;->)

JH.