There is a peculiar issue noticed, I need help understanding the reason and may be troubleshooting.

There is a microcontroller(87S52) based board with ADC and IO lines. The unit is programmed to operate for a time lets say T secs. When the board is used in the system in stand alone mode, I tend to get the run time as programmed.However, when the unit is operating close to a running motor, the runtime is T+30secs. Not sure why this is happening and how to resolve this.

I guess, someone here may have gone through similar issue. Request you suggestions to get through this.

 

Things like that have happened to my controllers when operating DC motors with brushes. Electromagnetic radiation from a noisy motor can cause the state of registers to change.

I your case you might find that either electric or magnetic shielding of the assembly will help. I/O leads as well as power supply connections can provide a pathway into the chip and those might benefit by the use of low pass filters. The only way to know how the noise gets in is by experimenting.