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'[EE]:PC Power Supply'
2000\06\04@221859 by Mitchell D. Miller

picon face
Mark,

>
> Hint:  This isn't a "low-noise" power supply.  You may want to use R-L-C
> filtering if you need cleaner power - don't know your needs.  For PIC
> projects I just down-regulate from 9V, works.  (7809 inside that panel.)
>

Is the noise enough to cause oscillatior problems on a simple SX project?
I've been trying to use the SX with the Murara resonator that Parallax
sells, but can't seem to make it oscillate.  Project works fine when
Parallax's SX Key is providing the clock.

Why do you choose to regulate down from 9v (which I presume comes from the
+12), instead of directly using the +5 the p.s. provides?  Noise?

-- Mitch

2000\06\05@042901 by Mark Willis

flavicon
face
Mitchell D. Miller wrote:
> Mark,
> >
> > Hint:  This isn't a "low-noise" power supply.  You may want to use R-L-C
> > filtering if you need cleaner power - don't know your needs.  For PIC
> > projects I just down-regulate from 9V, works.  (7809 inside that panel.)
> >
>
> Is the noise enough to cause oscillatior problems on a simple SX project?
> I've been trying to use the SX with the Murara resonator that Parallax
> sells, but can't seem to make it oscillate.  Project works fine when
> Parallax's SX Key is providing the clock.
>
> Why do you choose to regulate down from 9v (which I presume comes from the
> +12), instead of directly using the +5 the p.s. provides?  Noise?
>
> -- Mitch

I wouldn't expect noisy 5V to cause a resonator to fail to work - more
like to cause brownout problems and crash the SX Key (or repeated
resets?)  Scope Vcc and see what you see - per usual it's late before I
get back to e-mail <G>  Noise tends to CAUSE oscillations (at least when
inside the feedback loop) so I'd think something else is wrong?
(Haven't gotten SX's to the top of my dolist yet - Some day.)

Several reasons why I don't use the 5V directly - I figured the fastest
way to current limit this monster was to put a (2A fused) 7809 behind
the cover plate, that should protect things.  Then let out 9V at 1.5A
max, I used a regular PC style power connector (recycled a HDD connector
IIRC) to feed power to that PC board the 7809 lives on;  I didn't have
any PolySwitches and (at the time) my workbench suffered occasional
Severe Attack Of The Electronics-Eating Cat Incursions, thus fuse
popping was a distinct probability;  No problems yet.  (Have a small
resistor in series there - 0.1 Ohm, 1/2W IIRC - after the fuse & before
the cap across the In side of the 7809, not sure it was *needed* but I
figured it was a good de-coupling idea.  Don't remember if I 'scoped
across it or not!)  I hand-picked a 7809 with lowish Dropout Voltage
(under 3V, obviously!).  Debated using a 7808 with a diode in the base
lead but HAD a 7809 that worked <G>  (It might be some other reg., I
should go look!  Too darn busy here.  It's been a high-interruption
day!  ... life!  <G>)

A lower dropout regulator would be a better design;  I'd suggest at
least some good current limiting inside the PC's case - I like the idea
of using a blank panel as an interface, since it's PORTABLE, easy to
transfer *when* your PC power supply dies, & right there up front where
you need it to be;  Use what works for you.

Been too long since I scoped a PC power supply;  Take a look, it's noisy
in there.  My current O-Scope is a piece of crummy junk, saving to get a
better one.  Now I find it probably should be battery-powered, so much
for the 'scope I had been thinking of!

 Mark

2000\06\07@190915 by Andrew Seddon

picon face
> Is the noise enough to cause oscillatior problems on a simple SX project?
> I've been trying to use the SX with the Murara resonator that Parallax
> sells, but can't seem to make it oscillate.  Project works fine when
> Parallax's SX Key is providing the clock.

I have this problem too. Try plugging the SX-KEY in while the murata is in,
that works on mine.

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