Why does the Basic Stamp RESET periodically?

[Julia Goolia]

Hi,

I am running a basic stamp to control a step motor. My program looks
something like:

MAIN:
debug "start"
LOOP:
debug "LOOPING"
<some code>
GOTO LOOP

The weird thing is that when I run the program, the debug window will
first show "start", then "LOOPING LOOPING LOOPING" etc. However, now
and again, it will print "start" again without me touching the 9V
Duracell power supply. The BS outputs are going to a transistor array
which provides more power for the stepper.

Does anyone know why this happens?

Thanks!
juliabean

 

[CFoley1064]

From: [email protected] (Julia Goolia)

Date: 2/3/2004 7:20 PM Central Standard Time
Message-id: <[email protected]>

I am running a basic stamp to control a step motor.

The weird thing is that when I run the program, the debug window will
first show "start", then "LOOPING LOOPING LOOPING" etc. However, now
and again, it will print "start" again without me touching the 9V
Duracell power supply. The BS outputs are going to a transistor array
which provides more power for the stepper.

Does anyone know why this happens?

Thanks!
juliabean

Hi, juliabean. Some general observations:
* You aren't running that stepper motor off of the 5V output from the stamp,
are you? If so, have mercy on that li'l SOT-23 regulator, wouldja? Use a
separate power supply for the stepper, and wire the separate power supply
common and the stamp common together.
* Always try replacing the battery with a fresh (and known good) one first. If
your input voltage to the stamp regulator drops below about 6.5V, even for a
fraction of a second, a reset will be generated on board. One thing you can
try is momentarily placing a 330 ohm resistor across the battery while you're
program is running, and seeing if that causes a reset.
* Look at your layout. Make sure you're not getting even momentary overload on
any of the output pins. From memory, I think you can get about an extra 40 mA
out of the on-board regulator (check this) -- if you exceed that even
momentarily, the +5V drops and a reset goes out.
* Keep power wiring away from the stamp, and the signal input and output lines.
If you've got high current wires right next to signal wires, you're asking for
trouble.
* If you're driving relays, watch for contact arcing. That can upset the
stamp. Try to drive only resistive loads with relays, or if not, then place
the relays as far as possible from the stamp. Remember Sesame Street -- "The
Solutrion...To Pollution...Is Dilution!" Of course, that's not good enough for
the EPA, but the EMI from contact arcing is diluted by moving it farther away.

There may be more suggestions, but these have worked for me in the past.

Good luck
Chris

 

[Julia Goolia]

Chris,

Thank you so much for your suggestions! I really appreciate you
taking the time... I'm learning so much!

I have plugged in a 12V 200mA transformer (which plugs directly into
the wall) into the basic stamp (actually I'm using the BASIC STAMP II
OEM... I guess thats important!). I also use a transistor array and
the same power supply to power the stepper. That is, I am not
powering the stepper motor directly with the outputs from the stamp.
However, I'm not using a separate power supply either. That is, I
only have the 12V 200mA supply, and the + goes into the Vin pin and
the - goes to the Vss pin (I do not use the 5V Vdd pin). The + from
the supply also goes to the stepper wires and the COMMON input of the
transistor array. And, the - goes to the center tap of the stepper
and the ground of the transistor array (i think that is how it
goes...i'm at work right now so i can't check). Basically, both the
basic stamp and the stepper share a common ground.

One more thing I noticed: I have a new layout and it doesn't happen
with the step motor anymore... however, if I remove one the stepper
coils and replace it with an AMPMETER, it happens! Is it possible
that the AMPMETER is draining all the power so that the basic stamp
gets nothing? I thought the transformer would just suck more power
from the wall.

* Keep power wiring away from the stamp, and the signal input and output
lines. If you've got high current wires right next to signal wires, you're
asking for trouble.

Why is this? I guess its cause the current through the wire creating
a magnetic field which disruptes the current flowing through the
stamp? In my case they are quite close... about a few centimeters.
This may be the problem.

Thanks for your help once again... I'm going to investigate this
weekend.

And don't forget this from Sesame Street:

1 2 3 4 5 6 7 8 9 10 11 twe e e e e e elve.

juliabean