View Full Version : Program Resets Without Browning Out.......Motor Noise??

03-16-2010, 12:28 PM
· I'm currently testing a Tamiya Dual Motor and Gearbox combo with a Pololu Dual Serial Motor Controller.· I'm using four 1.5 volt AA cells for powering both the motors and an OEM BS2sx.·· My problem is my program keeps resetting and I suspect it is from noise.· I've soldered three
· .1 uf. capacitors to each motor (across both terminals and from each terminal to the·motor housing).·· At·any power setting above 10% ·(with or without a load) the Stamp program will reset.· The·Stamp Vdd is steady at 4.95 volts so I don't believe the brownout threshold is being crossed.· I placed another .1uf· capacitor across the Stamp Vdd and Vss terminals with no improvement.· ·I tested my program for any faults by disconnecting the motors from the controller and my program works fine without any glitches or resets.· Is there some more filtering that can be done or is it possible that it could be browning out very rapidly??···Can the motor cases be tied to common ground?· ·Sorry, I don't·have an O-scope at my disposal.·· The motor controller is connected per the documentation.· Thanks.

Phil Pilgrim (PhiPi)
03-16-2010, 12:53 PM
Do the AA cels also power the Stamp via a 5V regulator? What sort of caps do you have on either side of the regulator? Which regulator are you using?


03-16-2010, 01:08 PM
Hi Phil. I'm using the OEM BS2sx. Its the kit version that uses the 24-pin DIP SX chip. The voltage regulator is the LM2940-5.0. The power supply capacitor is 10 uf. UPDATE: I just added a 1000 uf. cap between the Vdd. and Vss terminals of the OEM board and the program is now working without glitches or resets.·· Does this mean that there was some lower frequency noise or maybe it was in fact browning out?· The 1000 uf.· is the only electrolytic cap I have laying around.· I need to stock up on caps.

Post Edited (Mikerocontroller) : 3/16/2010 6:27:06 AM GMT

Phil Pilgrim (PhiPi)
03-16-2010, 11:21 PM
The problem was that the 10uF cap was not big enough to maintain its voltage through motor transients. The chip was browning out. Also, if you read the LM2940 datasheet, you will see that it needs at least 22 uF for stability. I'd leave the 1000 uF cap on there, due to the motor.


03-17-2010, 06:33 AM
Thank you, Phil.· I will take your advice.

01-12-2012, 10:20 AM
decoupling , i guess try to decouple the micro and the motor.
micrro needs smooth supply any spike could make ur micro wild. make ur supply to this , it works for me so far.

put capcitor accross the motor , one 0.1uf ceramic and 100u traf 50V polar capacitor , this will kill both high and low frequency transients.

Best of luck