Brandeis University Physics 29a
Spring 2018 Kevan Hashemi

Lab 11: Decimal Display

In this lab you will build a circuit that presents a four-bit binary value as a single decimal digit on a seven-segment display. The construction itself is a challenge, because of the large number of gates you must connect together correctly. Your instructors will help you understand what you are supposed to do, but your objective is to design, build, and correct the circuit yourself.

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

Figure out how you are going to switch on and off individual segments of this display with 5-V logic levels. When driving one of the segments, we recommend a series resistor of 330 Ω. Do not connect any segment directly to 5 V, or you will destroy the LED within the segment. You have switches on your breadboard to supply 0 V and 5 V. Use four such switches to control four of the seven segments. Show an instructor your switching circuit.

Part 2: The four-bit binary number has value zero to fifteen, but we are going to display only numbers zero to nine, with digits 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. 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 value of the number as a decimal digit. Use your Karnaugh maps to obtain efficient boolean equations to implement the seven-segment logic. Show an instructor your work.

Part 3: Choose logic gates to implement your logic equations. Draw a diagram of your entire circuit. We recommend you use any or all of the following logic chips: 7400 (Quad 2-input NAND), 7402 (Quad 2-input NOR), 7404 (Hex Inverter), 7410 (Triple 3-input NAND), 7411 (Triple 3-input AND), 7430 (Single 8-input NAND), 7420 (Dual 4-input NAND), and 7432 (Quad 2-input OR). You will find a one-page diagram of the internal connections of these eight chips on the 29A web page. All of them come in a 14-pin DIP package. All of them require +5 V on pin 14 and 0 V on pin 7. Show an instructor your circuit diagram.

Part 4: Use four logic switches on your breadboard as input to your circuit. Use them so that the most significant bit of the four-bit binary number is on the left side. Build your circuit and demonstrate that all values zero to nine are represented correctly as a decimal digit on your seven-segment display.