[NCARC] Need help debugging electronics project

[scomind at aol.com]

Hi Ed,

So each blink is a 12V relay opening and closing? Does sound kinda like inductive kick from the relay coils. The diodes help but you might still be introducing noise into the +12V. But the stamp probably has a 7805 or similar regulator to reduce the +12V to +5, and that should buy you some noise isolation, unless it's the ground that's moving with the noise. Which relay lead do you touch to fix it, the +12V side or the driver transistor side? Have you terminated all IRQ, NMI, and similar inputs so they can't act as antennas and make the processor jump the track?

If I were building it I would use solid-state relays. Expensive to buy at retail, but lots of surplus brokers have them. You gain zero-crossing switching that way, too -- less EMI.

73,

Bob, WA9FBO

 

 




 

 

-----Original Message-----
From: Ed Gage <edgage at gmail.com>
To: NCARC Reflector <ncarc at mailman.qth.net>
Sent: Wed, May 30, 2012 3:46 pm
Subject: [NCARC] Need help debugging electronics project


I've developed a relay control based on the Basic Stamp, and need help
debugging it.  There is either some transient noise produced by the relays,
or some sort of surge.  I've put a diode across the coils which helped
control it somewhat, but I'm at a loss as to what is happening.

On powerup, 8 relays are charged with 12V, to drive 120V that runs 8
incandescent light bulbs.  The same 12V powers the Basic Stamp, which
controls the relays based on input from 8 buttons.  The project is a
"lock-out" game, where first press gets solid lamp, 2nd gets fastblink, and
3rd gets slowblink.  Additional buttons get no blink.  A reset to the Basic
Stamp resets the lock-outs.

What happens is when the second and third buttons are pressed, after
several blinks, sometimes the system resets itself, without user input.
 I'm at a loss as to why this happens.  However, I discovered I could
prevent the reset by touching one of the two leads for the relay.  My
assumption was that I was suppressing some sort of electric surge that was
happening with my body acting as a conduit to ground.

Perhaps somebody could elaborate on why this phenomenon occurs?

Anyone willing to come help would be treated to a nice dinner.

--Ed Gage, NØTVQ
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