A Dead Stamp II I/O Pin!? ULN2803
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Posts: 46,084
I had figured that the ULN2803 was a pretty robust chip, and that
I'd have no further problems controlling relays. I assembled the
vellum relay board kit as a LAST HOPE to control my LITTLE DC
motors without gitching anything. Did I miss something?
Everything seemed to be going just fine. I'm awfully discouraged.
About ready to throw my hands up in disgust with robotics.
I understand that the 2803 is reverse diode protected INSIDE, and
the only thing it's connected to is the relays. Why did it fry
an I/O pin on my stamp? Was it draining too much current? The
vellum board didn't have a spot to place resistors on the inputs
to the 2803's.
It didn't hurt my other BSII connected to the same BIG battery.
Both stamps are run through a separate 7805 regulator and I've
noticed no peculiar activities from either of them. There's an
LED display connected through a shift register to my other stamp,
and the CMOS shift register (normally rather jittery until I
found that you had to connect both serial inputs together), never
complained.
I'd have no further problems controlling relays. I assembled the
vellum relay board kit as a LAST HOPE to control my LITTLE DC
motors without gitching anything. Did I miss something?
Everything seemed to be going just fine. I'm awfully discouraged.
About ready to throw my hands up in disgust with robotics.
I understand that the 2803 is reverse diode protected INSIDE, and
the only thing it's connected to is the relays. Why did it fry
an I/O pin on my stamp? Was it draining too much current? The
vellum board didn't have a spot to place resistors on the inputs
to the 2803's.
It didn't hurt my other BSII connected to the same BIG battery.
Both stamps are run through a separate 7805 regulator and I've
noticed no peculiar activities from either of them. There's an
LED display connected through a shift register to my other stamp,
and the CMOS shift register (normally rather jittery until I
found that you had to connect both serial inputs together), never
complained.
Comments
Don't give up, I seemed to have zapped a pin on my BS II also....and one of
my BS 1 pins won't work inside the carrier board but will work outside the
carrier board! I think parallax summons evil sprits to put in the stamps! I
can hear them now: Boil, Boil, toil and trouble....this stamp pin won't work
for much longer.....MUUhahahahahah!
I have heard that putting 220ohm resistor on the stamp lines can add extra
protection. Another option is to use optoisolators. That would mean you use
an IR LED and an IR photo transistor or diode detector and pair them up so
that the stamp output to the LED and the LED sends the signal to the
detector. This would isolate the stamp from the motor control circuit. You
probably don't need to do that though, it's just an option I thought I would
suggestion.
Don't give up on your stamp controlled robot yet, hang in there...it'll all
start working right sooner or later!
-Justin
The Robotics Club of Yahoo (TRCY)
From newbies to pros we have over 700 members from across the globe!
http://members.tripod.com/RoBoJRR
connected if you connect the relay's supply voltage to the Cathode Pin on
the 2803.
Don't give up. Some "road kill" is unfortunately a part of the learning
process.
You might consider our Homebrew BS2. Admittedly, not as convenient in
assembly, but less than half the price ($21). A replacement PIC is $10
which makes a loss a bit more palatable.
Peter H. Anderson, Morgan State University
pha@p..., http://www.phanderson.com/stamp/
Basic Stamp Starter Packages, Homebrew BS2
Original Message
From: Anubis <mikorians@y...>
To: basicstamps@egroups.com <basicstamps@egroups.com>
Date: Saturday, April 29, 2000 11:24 AM
Subject: [noparse][[/noparse]basicstamps] A Dead Stamp II I/O Pin!? ULN2803
>I had figured that the ULN2803 was a pretty robust chip, and that
>I'd have no further problems controlling relays. I assembled the
>vellum relay board kit as a LAST HOPE to control my LITTLE DC
>motors without gitching anything. Did I miss something?
>Everything seemed to be going just fine. I'm awfully discouraged.
>About ready to throw my hands up in disgust with robotics.
>
>I understand that the 2803 is reverse diode protected INSIDE, and
>the only thing it's connected to is the relays. Why did it fry
>an I/O pin on my stamp? Was it draining too much current? The
>vellum board didn't have a spot to place resistors on the inputs
>to the 2803's.
This topic has come up recently. You *will* destroy output pins on the
'2003 if you do not provide back EMF clamping for the relay coils. The
diodes needed to do this are already inside the '2003 but you *have* to use
it! Run a wire from pin 9 of the '2003 to the + supply that the other side
of the relay coils is connected to. Should be the end of your problems.
If you do not have access to that + supply, you can make a simple RC clamp
from a 10 uF capacitor and a 10k resistor connected in parallel from pin 8
to pin 9 of the '2003, with the + lead of the capacitor connected to pin 9.
dwayne
Dwayne Reid <dwayner@p...>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(780) 489-3199 voice (780) 487-6397 fax
Celebrating 16 years of Engineering Innovation (1984 - 2000)
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