$1.$ Seven$-$Segment Display

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A seven$-$segment indicator is used to display any one of the decimal digits $0$ through $9.$ Usually, the decimal digit is available in BCD$.$ A BCD$-$to$-$seven$-$segment decoder accepts a decimal digit in BCD and generates the corresponding seven$-$segment code as shown below.

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Figure below shows the connection necessary between the decoder and the display. The $7447$ IC is a BCD$-$to$-$seven$-$segment decoder$/$driver that has four inputs for the BCD digit. Input D is the most significant and input A the least significant. The four$-$bit BCD digit is converted to a seven$-$segment code with output a through g$.$ The outputs of the $7447$ are applied to the inputs of the $7730($or SA$03-12$HDB$)$ seven$-$segment display. This IC contains the seven$-$segment light$-$emitting diode $($LED$)$ segments on top of the package. The input at pin $14$ is the common anode $($CA$)$ for all the LEDs. A $47-$W resistor connected to Vcc is needed in order to supply the proper current to the selected LED segments. Other equivalent seven$-$segment display ICs may have additional anode terminals and may require different resistor values. The seven segment SA$03-12$HDB works fine with the $7447.$ When using SA$03-12$HDB$,$ the inputs need to be connected instead to the ground $($not Vcc$).$