noise problem for At89s52

[rutvik1588]

Hi guys. I've made a project based on AT89s52 with rs-485 serial communication protocol, it works good in normal conditions (without much noise).But it is actually intend to work under heavy electrical noise environment. When it is placed near heavy AC load lines , many times the micro-controller starts malfunctioning. The behavior of micro-controller is unpredictable and sometimes it is automatically resets to the beginning of the code execution. Here i am attaching the circuit diagram.

Please help me how could i prevent the heavy electrical noise to my 89s52.

 

[sei]

hi rutvik1588,

one way to solve noise issue:
1) place larger capacitance coupling at the power supply i.e.100uF parallel with your 5V. it will absorb noise from the line.
2) make pcb and use ground plane.
3) dont place near ac line because you supposed not to placed uc near the ac lines. EMI from ac line exhibits noise. that's why engineers prefer PLC rather than uc to run thier automation system because PLC more robust and has higher noise immunity.
4) if you have no choice, make a good casing for your uc and make sure ground your casing to ground as well.
5) dont share supply (AC point) with your ac machines. noise will leak from the point into ur dc adapter

 

[klystron]

Use both an electrolitic and a ceramic capacitor between the 5 VDC and ground. The ceramic will take care of the high frequency noise. Electrolitic capacitors become inductive at high frequencies. Bias yor RS485 to +5 and ground with 200 ohm resistors. Use an opto isolators to galvanically isolate your micro from the RS485 net (that acts like an antenna)