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Microcontroller RESETs (somtimes) when Contactor energizes

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blacksnow

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In my project, i am interfacing 89s51 with drill machine's motor. (The block diagram is in the attachment). The sensor generates pulse when gear is passed in front of it. After specified pulses 89s51 stops the motor and when direction is reversed the motor moves in other direction (through other contactor not shown). The required result is achieved but when the contactors are energized it sometimes RESETS the controller and sometimes shows unwanted character on LCD.

I have not connected any buffers or opto-couplers in this design.

PLEASE help me to get rid of the resetting problem and also suggest me some buffers or opto-coupler ICs or any other IC that is required with this design.

Thanks
 

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  • Motor Control.bmp
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before testing with optocouplers , first make sure that 5v supply for 8051 has adequate rf bypass.
this is one possible source for 8051 resetting and lcd goes out when contactor is energised.
 
Add some 440V MOV (Metal oxide variastor) between Relay contacts... (C & NO, C & NC) & Contracor Phase & neutral... & Input Phase & neutral.... Also add a 103 disc capacitor between pulse PIN & GND... Better use any transisor to drive relay... (in your shematic shows directly controle relay)
 
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