Naughty Micros Crazy Programer.

Hi,

I have two PCBs namely X and Y for the same application and three ATMEL 8951s namely A,B and C.

the layout of both PCBs is different. PCB Y doesn't have ULN2003 and drives relays thru transistors. The telephone line loop also is sequeezed closely.

PCB X has ULN2003 to drive relays. The telephone line runs accross the board.


micro A runs very bad on pcb X. micro B runs often bad on pcb X. micro C runs well on pcb X.

All micros run well on pcb Y.

What I have done:

I have put extra diodes right the coils of relays and have tried to keep the offhook loop of telco line away from the board.

This has improved the situation that micro A now runs only a little better.

I shall try to completely sequeeze the telco traces on pcb and shift the relays to the other side of the board in order to keep the loops shortest as in PCB Y.

But the strange thing is why the micros are different in behavior ??? Does ATMEL produce micros with different noise immunity ??

Kindly also comment that this problem relates only to the pcb and hardware and not the code.

Regards

Babar