[sdiy] D Flip Flip start-up state

[Czech Martin]

If you build a PSU for some bigger system, a PON signal (power on)
that is comming out of the PSU is certainly a good thing.
Maybe also a power down alarm. The PSU can see that the
filter caps are running low and create a power down alarm
seconds before the regulated voltages will drop out.

Can be used for silencing pops, or saving data to non volatile,
etc. etc.

m.c.

> -----Original Message-----
> From: harrybissell [mailto:harrybissell at prodigy.net]
> Sent: Montag, 1. September 2003 06:40
> To: Ray Wilson
> Cc: Dave Magnuson; synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] D Flip Flip start-up state
> 
> 
> oh yeah... you can build only one of these circuits and use 
> it to reset all the
> logic in the whole circuit... called a 'power up reset' 
> (funny that :^)
> 
> H^) harry
> 
> Ray Wilson wrote:
> 
> > Hi Dave
> >
> > I would give the reset a nice long pulse during start up. 
> Here is how. Use a
> > CD40106 hex schmitt inverter. Place a 10uF cap at an input 
> along with a 1
> > Meg to V+.  When the power is off the resistor will 
> discharge the cap into
> > the circuit. When the power is applied the cap will have a 
> low level which
> > will cause the CD40106's output to be high which will hold 
> the flip flop
> > reset. After the cap charges via the 1 Meg to 2/3 of the 
> supply voltage the
> > output of the CD40106 will go low which will not affect the 
> flip flop's
> > operation after that. If you want the cap to discharge very 
> quickly when
> > power is removed then in addition to the 1Meg to V+ place a 
> diode (anode to
> > the CD40106 input the cap is on, kathode to V+). That way 
> when power is
> > removed the cap will discharge much quicker into the 
> circuit via the diode.
> >
> > Hope this helps
> >
> > Ray
> >
> > -----Original Message-----
> > From: owner-synth-diy at dropmix.xs4all.nl
> > [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Dave Magnuson
> > Sent: Sunday, August 31, 2003 10:41 AM
> > To: synth-diy at dropmix.xs4all.nl
> > Subject: [sdiy] D Flip Flip start-up state
> >
> > 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
> 
>