Lab 11: Decimal Display

You will build a circuit that presents a four-bit binary as a single digit on a seven-segment display. The construction itself is a challenge, because of the large number of gates you must connect together. Your objective is to design, build, and correct the circuit yourself.

Part 1: We will use a MAN72A or equivalent seven-segment display. The drawing below shows how the LEDs of the seven segments are connected to the fourteen pins of the package. You will find the MAN72A family data sheet on the 29A web page.

Figure out how you are going to switch on and off individual segments with TTL logic levels. When driving one of the segments, we recommend a series resistor of 330 Ω. You will damage the display if you apply 5V directly to any of its sgegments.

Part 2: A four-bit number has value zero to fifteen, but we are going to display only zero to nine. For each segment in the display, make a Karnaugh map that relates the four bits of the number to the state of the segment, so that the segment will illuminate correctly to display the decimal digit that represents the binary number. Obtain efficient boolean equations to implement the seven logic functions.

Part 3: Choose logic gates to implement your logic equations. Draw a diagram of your entire circuit. You will find a one-page diagram of the internal connections of eight useful logic chips on the 29A web page. All of them come in a 14-pin DIP package. All require +5 V on pin 14 and 0 V on pin 7.

Part 4: Use four switches to generate a four-bit binary number. Build your circuit and demonstrate that values zero to nine are represented correctly as a decimal digit on your seven-segment display.