Problems with 12F675


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  1. #34
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    Hi Fratello,
    Ok, in the crude drawing I posted, R3 is selected to limit the current going through the relay coil. r1 is selected to limit current going into the transistor's base, and R2 is the trick. R2 needs to be smaller than R3, but not so low a value so as to inhibit the transistors operation. R2 will increase the ON current, but should help drive the transistor to "cut off".
    in this link:http://engr.astate.edu/jdg/Electroni...orBiasing.html
    Scroll down to Figure 5.
    RC is your relay coil represented as a resistor
    R1 is the resistor from the pic port, I know it is shown as connected to Vcc, but when your port goes high that is exactly what you have
    R2 is the "pulldown resistor, causing cutoff
    RE is the current limiting resistor for the load.
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