Dear sir We have designed a circuit for switching ON and OFF electrical loads (of capacity 3KVA to 100 KVA) using electrical contactors and also controlling/varying the input voltage to the load using multiple tapped auto transformer. The contactor and the tap changing is controlled based on inputs from real time clock and control program in the microcontroller Atmel 89c51. We are observing that the time in the real time clock is getting corrupted and microcontroller program is reset after the changed time.This usually occurs when the electrical loads are switched On or OFF. Please suggest us the reason.We have tried to take care of EMI by enclosing the PCB in a metal box. Regards Vishnu
What have you done to the formatting of your message?! Use the 'Preview' button to check formatting (and to proof-read) before posting! You don't need to keep pressing return - the forum automatically does the line wrapping! "the time in the real time clock is getting corrupted and microcontroller program is reset after the changed time.This usually occurs when the electrical loads are switched On or OFF ... We have tried to take care of EMI by enclosing the PCB in a metal box" A metal box should help against radiated emissions, but what have you done about conducted interference? Does the load switching cause the microcontroller's power supply to "droop", or do other nasty things to it?
http://www.8052.com/faqs.phtml?FAQ=119926 Erik