RE: Electronics Question...

["Ian Lowe" <ian@xxxxxxx>]

*ahem* and the prize goes to Frank..

"yeah, of course my circuit has decoupling caps on the PIC"
errr..

add a decoupling cap, and all is well, regardless of power issues!

Ian.

-----Original Message-----
From: Ian Lowe [mailto:ian@xxxxxxx]
Sent: 27 December 2002 10:38
To: ukha_d@xxxxxxx
Subject: RE: [ukha_d] Electronics Question...


Yep Dave,
Thanks for the pointers (and thanks to all of the people who mailed me
directly!)

The circuit is an interface for controlling the K400 Curtain controller,
and
the problem seems to be twofold:

My PCB is missing two caps around the voltage regulator, and the regulator
itself is simply not powerful enough.

I'm off to craplins in a mo... wish me luck!

I.


-----Original Message-----
From: Dave McLaughlin [mailto:dave@xxxxxxx]
Sent: 27 December 2002 10:29
To: ukha_d@xxxxxxx
Subject: RE: [ukha_d] Electronics Question...


Hi Ian,

What other devices are in your design? The 78L05 is only capable of
supplying 100mA max current and above this the voltage starts to drop as it
heats up.

I normally see this when using a few LED's in the circuit but not knowing
your design it does not help. There is a higher rated device in the same
package available from the likes of Farnell and RS but I can't remember off
hand what the part number is. If you need it give me a shout and I'll look
it up.

Regards
Dave...

-----Original Message-----
From: Ian Lowe [mailto:ian@xxxxxxx]
Sent: 26 December 2002 18:55
To: ukha_d@xxxxxxx
Subject: [ukha_d] Electronics Question...



Been debugging one of the wackiest problems I have ever seen over the
festivities, where writing a value to EEPROM failed (although the rest of
the circuit worked perfectly) After some helpful souls trying the code out
for me, I figured out that the problem was power related. :

I'm using a 78L05 to derive a 5V supply from a 12V feed, and only getting
4.7 Volts (!!) which is great, right up until the PIC tries to do something
juice intensive, at which point, it fails..

I have tried dropping a 220u cap across the 5v-0v feed, thinking that would
give a little reserve for intensive ops, but no joy..

I don't want to bore the bits off of the list at large, so can anyone who
wouldn't mind giving a point in the right direction drop me a mail?

Ta muchly, and I hope that yesterday's dinner has largely settled by now ;)

Ian.

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