[NCARC] Need help debugging electronics project

[scomind at aol.com]

Hi Ed,

Not sure how you have the buttons wired. Do you have pullup resistors and use the buttons to ground them, sending a logical zero to the processor when the button is pressed? Or do you have the switches wired in series from the supply back to the micro, sending a logical one when pressed? If the latter, do you have pulldown resistors so that the processor inputs don't float?

In either case, are you feeding multiple 30' wires from the output of the 7805 regulator? If so, that wiring may be acting as an antenna and feeding noise into the Vcc pins of your micro and the other logic (especially since your test switch board works okay). I'd keep the processor's +5 V supply away from the outside world, if for no other reason than to prevent someone from static-zapping your logic by touching the button wires. Maybe use a separate regulator to power the buttons if you need 5 V logic levels. Or, drive the buttons from your unregulated +12 V supply, then use NPNs to level shift the signals back to 5 V.

73,

Bob



 

 




 

 

-----Original Message-----
From: Ed Gage <edgage at gmail.com>
To: NCARC Reflector <ncarc at mailman.qth.net>
Sent: Thu, May 31, 2012 3:25 pm
Subject: Re: [NCARC] Need help debugging electronics project


Thank you all for your replies.  I see that additional information is in
order.

First off, as AF6KD observed, I am using a "kit" relay board if you will:
   http://www.futurlec.com/Relay_8.shtml .  Sadly, as WA9FBO pointed out,
the solid-state board (http://www.futurlec.com/SSRAC.shtml) did not exist
when I began this project.

However, it was nice to have 50% of all the parts for the project already
mounted, with contact points, etc. so I went with the former board.

I modified this board in 2 ways:  #1, I tapped the 12V with a 7805 (as
WA9FBO already guessed) to power the on-board IC, and the Stamp, and I also
wired the 1N4001 diodes across the coils.

Also, as WA9FBO guessed, there is an on-board power regulator that turns
whatever slop power you put into the chip into clean 5V.  I'm using that
output to power the buttons.

The Basic Stamp II spec says there's a limit of 40mA source, 50mA Sink per
8 I/O pins.  I overcame the source limitation on the source pins by using
transistors to drive the relays (as AF6KD and Steve both had guessed) so
now they don't have to work so hard .  Also, at power-on, all relays are
closed.  The lights are wired to normally-open, and only flash as relays
are "relaxed".

I'm not able to get a good reading of the load as Steve suggests, because
of my digital multimeter.  Oh, how I miss the cheapie analog multimeter I
had as a kid.  However, even with the slow refresh of the reading, I'm
still seeing over 5V on VCC, with no brownout.

That being said, now I'm leaning towards the input being the issue.  The
eight buttons are each at the end of a 30' run of wire.  Although the wire
is shielded, I'm guessing it's not the best quality wire, and requires more
of a current load to operate, even if not engaged.  I'm guessing
the capacitance of the wire is enough to draw the current off the board and
cause a reset of the BSII.  As proof, if I replace the eight button
interface with my test input board (
http://www.futurlec.com/TrainingBoardAccessories.shtml - 2nd one down),
works flawlessly.

I noted that the test input had 10K resistors, so I originally wired the
long-run push buttons the same way.  Did not seem to make any difference.

Still doesn't explain the reason why when touching the + side of the coil
for each relay causes the system to behave, but I like Steve's explanation
that I have an "electric" personality.

--Ed
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