7 segment displays are used to display digits ranging from 0 – 9. They are made up of LEDs arranged in the shape of the number 8, as any of the ten digits can be formed from the shape. A different number is displayed based on the combination of the lit up segments on the display.
BCD (Binary Coded Decimal) decoders are needed to use the display. The decoder translates four digit binary code representing each of the digits into signals, for each of the seven (or eight, counting the decimal on some displays) segments.
In order to observe the functionality of this display, I recreated a circuit from the element14 website. The components of the circuit includes:
- 4x manual switches
- 4x LEDs (they will be used to indicate whether the switch is on, so the color makes no difference)
- 74LS-47 decoder chip
- 7x 470 ohm resistors
In this circuit, the binary value is going to be input manually, with each of the four switches corresponding to a single digit out of the four. The switches are connected to LEDs, which will make it easier to recognize which switches are triggered.
In turn, the switches will be connected to the four inputs on the decoder – A, B, C, and D. The outputs are connected to resistors leading to each of the segments on the display. Images of the final result are shown below.
