[sdiy] D Flip Flip start-up state

[Dave Magnuson]

Hi List,

I'm currently designing a circuit that uses a momentary puch button to
create an A/B switch.  The design is simple, and I'm sure most of you have
seen or used it before:

A momentary push button is debounced and shaped to create a clean logic
pulse.  This pulse is then sent to a D flip-flop (basically a divide-by-two
circuit).  The flip flop is wired with the incoming pulse to the clock
input, the Q output goes to the next circuit stage (relays in this case),
and there's feedback from "not Q" to D.

Well, here's my question:  I know that during power up I'll end up with a
random setting.  Is there any way to force the flip-flop to always reset to
the same position when powered up?  I don't need it to have "memory" where
it always defaults to the last position used before it was turned off... I
just want it to always come on in the same position.

Since the output from the debouncer should be logic low at start up
(assuming no one's touching the button), I'm wondering if I could simply
pulse the flip flop's reset line at power up, but I'm not sure of the best
way to generate this one-shot without too much circuitry.  Any ideas?

Thanks everyone,

Dave Magnuson

Resonant Frequency:
resfreq at hoohahrecords.com
http://www.hoohahrecords.com/resfreq/index.html
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