papunblg
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In the given schematic, the sensor’s Vout terminal voltage is 4.4Volts. When it senses, the sensor’s Vout terminal voltage drops to 2.61 Volts. As both the values are more than logic low value of the PIC micro, a transistor is used to act as a switch to provide high and low logic for the PIC16F84A. It is suppose to work in saturation. With a BC547B(Min Hfe 200) R1=1K and R2=10K, the circuit is working as expected. Although, my calculated value shows for R2=10K, current through R2 is 0.5mA.So for min Hfe200, R1 should be 1.48K for required base current of 0.0025mA.
My question is, in this case where no big loads (like relay or leds or other components) are present, what is the minimum collector current possible so that PIC can sense it? Or what is the maximum value of R2? Am I missing something?.
My question is, in this case where no big loads (like relay or leds or other components) are present, what is the minimum collector current possible so that PIC can sense it? Or what is the maximum value of R2? Am I missing something?.