Logic Gates Puzzle 10

The overall shape of the circuit is a hint.

Have a look at the outputs, why they have letters and not numbers?

A real circuit like this would have four inputs, not only three. It makes it so much more useful.

The outputs are connected to seven LEDs which are arranged in a special way.

This circuit is a 7-segment display driver with only 3-bit input. It displays the digits 0 to 7 on an attached 7-segment display.

You find more details about 7-segment displays on this Wikipedia page. Here you also find the common assignments of the letters A to G to each segment.

Real-World Design with Matrix

To build a complete 7-segment driver, you start with a binary decoder. The decoder will convert the binary encoded numbers from 0000 to 1111 into 16 distinctive signals.

Then you create a matrix from these 16 signals and the seven outputs. If a segment should light up for one of the 16 distinctive signals, you connect it using a diode.

For a wonderful example, see Fran’s great video about diode steering.

• The circuit displays the digit 7 in an alternate form, adding the segment F. Do you find out, why this decision was made?
• Design a circuit that displays a signed 4-bit number, including the existing digital circuit. The minus sign will be an additional output I_minus.