This circuit is really for multiplexing four 7-segment LEDs. I expanded one of the 7 segments to show all of its LEDs separately. I'm trying to understand how the transistor goes into saturation when the microcontroller (uC) applies 5 volts to it digital pin.
If the uC has 5 volts on pin 5 and 0 volts on say pin 21 it doesn't seem like "LED for segment A" would turn on because the diode initially acts like an open circuit thus not allowing the proper forward bias to be put across the base-emitter junction of the transistor.
If the uC has 5 volts on pin 5 and 0 volts on say pin 21 it doesn't seem like "LED for segment A" would turn on because the diode initially acts like an open circuit thus not allowing the proper forward bias to be put across the base-emitter junction of the transistor.
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