Troubleshooting Pololu 18v25 simple motor controller serial error


I am working on a simulator and I am using 2 pololu 18v25 SMC to control two 12V PMDC motors with the help of arduino mega 2560 and potentiometers. The connections from SMCs are as follows:

Vin - 12V power supply
OutA - +ve of motor
OutB- -ve of motor
Gnd - Gnd of power supply

Serial connections:

Rx - Tx of arduino mega 2560
Gnd - Gnd of arduino mega 2560

The SMC is connected to a computer via USB.

The problem I am facing is that, the SMC 1, used to control the left motor is showing some serial noise and frame errors, but it is driving the motor and it brakes whenever there is serial error. The SMC 1 is brand new since the old one was damaged and I have checked the left motor with the SMC 2 (which controls the right motor) and it works fine.

I have checked for grounding issues and could not find any problem with that. Also i have changed the soldering, but it did not solve it either.

As a next step, I have given various speeds (with a simple program to drive the motor forward) to SMC 1 to drive the left motor. At a continuous speed of 500 (max speed 3200), there is a continuous serial error for approximately 5 seconds and from then it works fine. Again at a continuous speed of 600, there is a serial error for approximately 7 seconds: This duration of getting serial errors increases with increase in speed. The motor still drives with intermediate braking during the time of serial error and after a few seconds it is driven perfectly by the SMC1.

Kindly advise me what has to be done to remove this error.

Thanks in advance.


Hello, Hari.

Do you get the same serial errors if the motors are not connected? What baud rate are you using for your communications? Can you post pictures here that show your system and where the wires run?


Hello Nathan,

I am not getting serial errors when the motor is not connected. I am using baud rate of 19200 for communication. The pics of the system is uploaded below. The blue wire is connected to ground and the brown wire is connected to 12V of power supply. Serial communication: orange wire to Tx of arduino and blue wire shares a common ground with arduino.


It looks like the connection between your motor driver and the Arduino is a bit circuitous and has a lot of intermediate connections. A more direct connection might help. Also, it looks like the high current power supply lines for the motor driver cross and run parallel to the serial data line for a little bit. Routing the high-current wires away from the signal wires could help.

If you still have problems after making those changes, you might also see if a lower baud rate like 9600bps helps.


Hello Nathan,

Thank you for your help.

I have made direct connection as you suggested and also reduced the baud rate to 9600bps, but both did not help.

Then I interchanged the SMC1 and SMC2 and both were working individually, without serial errors. But when I connect them parallel to the power supply, both shows serial errors!


Do you have a datasheet or any other specifications you can provide for the motors and power supply?