Error after 100 calls

I’m using the micro controller in Pololu-Mode with POB-Bridge on a NXT-Brick with LabView 7.x
Everything works fine.
But I found out that after aprox. 100 calls there are more and more often errors on the pololu-Board (red LED).
Baud Rate is 9600.
Cable-Length ca. 5 cm.
I’m using the TTL-Input.

I hopr that somebody can help me.


I’m not familiar with the POB-Bridge, but if the error happens once in a while, it could be a problem with the serial data generation on that board or a noise problem with your general setup. How are you powering everything? Do you get the same problem whether or not servos are connected? If you’re powering everything from one source, it might not be able to keep up with the varying load of the servos, causing fluctuations in the supply that causes serial data to be misinterpreted. Do you have access to an oscilloscope to look at the serial data? If the problem is with the POB-Bridge, a last resort you could have is to occasionally reset the servo controller using a digital I/O line.

- Jan

Hello Jan,
I have tried to use different power sources.
The Error occurence seems to go a little bit down, but it still happens.
The idea with reset-line works well. I am using it already.
I make a reset every time before changing the Servo-Position - But sometimes there have to be two resets before it is working again.
The controller and the POB-Brige are powered with six 2700 mAh NiMH AA rechargables.
The Servos are powered by the same source via a 5V-Power Stabilisator (7805).
I have only wired the input line.
In Other posts I have seen, that slowing down the baud-rate can be a course of action.
I can think about a software-solution via a digital pin but I don’t know if I will be able to generate proper frequnces.
It would be fine if you could give some more tips.
cheers, Olaf

I think your power supply is to blame for most of your problems. A linear regulator like the 7805 is usually not a good option for powering loads such as motors, and using the same supply for your motors and electronics can introduce a lot of extra noise. Can you try connecting a separate, 4-cell power source to the servos and see if that changes things?

- Jan

An extra battery-Pack does not show realy good results and is not a realy good solution because of the extra weight to be carried by the biped.

I applied a hardware solution.
I’m usinf now an acceleration Sensor to mesure the tilt of the bot.
If it has not tilted I make a Reset and try again.
After max two resests signals are coming through.
Cheers, Olaf