Hello, I've been experimenting with BS2 bot and ran into "nervous
servo" problem - servo was turning by itsself even when pulse wire was
not connected. AND, BS2 restarted each time this happened. So, I
thought that servo drains power for a moment (4 AA batteries). BS2
also has two UCN5804 stepper driver chips hooked, using 4 stamp
outpins ( 2x pulse and direction signal). Steppers power source is
separate 12V small acid lead battery (1.2Ah). So, I thought that when
I power BS2 from a big 12V battery, the problem might go away. I
switched it over and it worked good. BUT - after while StampWorks
didn't find BS2 anymore :((
What's odd, is that stamp itsself seems working, because one stepper
is turning as supposed.
Is the stamp dead or what?
Was the pulse wire floating? By that, I mean was it completely
disconnected and not hooked to anything else. If so, you were toggling the
pulse wire through "antenna effect". Never leave a live input floating
because you don't know what conditions are really present. It should have
been properly terminated with either a pullup or pulldown resistor. If it
is a CMOS device, you have probably destroyed it if you left an input
How is the power supply pin bypassed on the Stamp chip? You should have
at least 100nF and more appropriately, 10 uF directly from the power to the
ground pin as close to the Stamp chip as possible.
Possible, but if that were the case, your batteries would be low (or it
would never work properly under normal operating conditions!)
The first clue that this is not a good idea is that you are getting
problems through some pathway that does not involve the power supply. If
you have separate power for the logic and the motors, and you are still
getting glitches, then this is either a faulty device conducting noise back
through to some critical part, or you have EMI problems- electrical noise
spikes from the motor (an inductive device) inducing glitches in the logic.
Sounds like you do not have surge suppression or other badly needed
snubber hardware in place. You have very likely done some permanent damage
to the Stamp chip.
Then perhaps the serial communications pin(s) have taken a hit, but
without them, you are not going to be reprogramming your Stamp any more.
I would say so. Without a look at your schematic, it is hard to say
exactly what caused the problem, but I would focus on the driver chip first
for that servo that was moving- you left a lead disconnected and that is not
good. Probably, you have damaged the servo driver at the outset.
Then, being damaged, it probably carried electrical spikes from the
motor through the rest of the circuit and like dominoes, things started to
fail. Replace the servo driver chip first, then add capacitive decoupling
to the Stamp, and then see if it functions properly. But be prepared to
have to buy a new Stamp because it sounds like you have lost the ability to
program that one.
What could be happening if you are running everything from 6V (4 cells) is
the servos are drawing too much
power and going into a jitter mode because the stamp voltage is not
constant. I have seen this first hand.
The solution is to run the stamp using its power supply (supplied with
9V-12V etc.) and run the servos from the 4cell /5-6V system. If you only
want one power supply you should use something high enough that will
allow the stamp to use its supply, then maybe use something like an LM7805
as a +5V source.
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