Voltage drop affects sensor reading
I asked here because its been 3 days solving this problem. Finally i got a solution.

The arduino forum which is included in my post has a solution for the problem but didnt solve mine. There is an answer to separate the GND pin of the relay to another GND pin in arduino but this doesn't solve my problem. What i did is separate both GND pin and VCC pin in the MB90F387s. That solved my problem. Thanks for everybody who wants to help.