PIC16f877A resets due to external noise

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  • #1089
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    katrina
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    I have faced this problem many times that I connects Relay with pic microcontroller and whenever I put Load on Relay’s Contacts PIC16f877a(http://www.kynix.com/Search/PIC16f877A.html) resets. I some time solve this problem by triggering another relay from basic relay attached to PIC. But this is not a solution. Can any one describes Why pic is affected with this relay spark. And what is really happening which causes pic to reset. Following things I have kept in mind while building circuit
    I have 1K Pullup resistor on pin 1 (Reset pin) of Pic 16f877a
    Fuses are, Power up timer = enable, Brown out detect = enable, LVP= disable, CP=enable
    Power supply is filtered, ceramic capacitor of value .1uf connect across both ends of regulator
    Crystal is 4MHz, and 33pf capacitor across crystal are close to (Circuit works fine, problem of reset occurs only when relay turns on with Load connected)
    Relay is used of 12v/5amp ratings
    C945 NPN Transistor is used to drive the relay
    Reverse biase 1N4148 diode is connected across relay coil to save reverse leakeage
    I never faces such problem in Atmel 89c51 microcontroller with same relay interfacing circuit. It is PIC who goes reset every time. But if do not connect any load to relay the circuit works fine. No reset occurs. Can any-one describes what is the issue with PIC?

    #1433
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    TamiDuke
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    Post count: 1

    Just connecting everything to a ground net would be fine if nothing has any ground current. Of course various parts do. This current times the impedance back to the one point you get to call ground causes a offset voltage. Don’t just think of ground in terms of DC. DC is the easy part. Consider the series inductance of any connection and then the high frequency ground return currents that run accross that connection.

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