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7-SegmentDisplayDecoder
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Activity 2.3.2 — Seven-Segment Display

Learning Objectives

By the end of this lesson, you will be able to:

  1. Identify the seven segments (a-g) and explain the difference between common cathode and common anode configurations.
  2. Map binary-coded decimal (BCD) values to the required segments for digits 0-9.
  3. Wire a BCD-to-7-segment decoder circuit with proper current-limiting resistors.

Materials

  • 1 Common Cathode Seven-Segment Display
  • 1 74LS47 or 74LS48 BCD-to-7-Segment Decoder
  • 7 330 Ω Resistors
  • Digital Trainer or 5V Power Supply
  • Jumper Wires
  • Optional: Multisim / Wokwi for simulation

Part 1: Display Anatomy

A seven-segment display uses eight LEDs (a-g + decimal point) to represent digits and letters.

7-segment display anatomy

Common Cathode vs Common Anode

| Configuration | Description | Logic to Light Segment | |--------------|-------------|-------------------------| | Common Cathode | All cathodes to GND | HIGH (1) | | Common Anode | All anodes to VCC | LOW (0) |

Part 2: Procedure — Digit Mapping

Complete the truth table below by determining which segments must be illuminated to display the digits 0-9. Use “1” for ON and “0” for OFF.

Digit Mapping Task

  1. Study the segment layout (a-g) shown in the diagram above.
  2. Click each cell in the truth table below to toggle it ON (1) or OFF (0). The seven-segment preview updates in real-time so you can verify your answer visually.

Seven-Segment Truth Table

Click cells to toggle: empty → 1 → 0 → empty
Selected Digit
Seven-segment display preview of your answer: no segments lit
0
Segment Layout:
 a  top   b  top-right   c  bottom-right
 d  bottom   e  bottom-left   f  top-left
 g  middle
Digitabcdefg
0
1
2
3
4
5
6
7
8
9
Fill in all cells to submit

Part 3: Procedure — Circuit Construction

The Decoder

The 7447/7448 IC takes a 4-bit BCD input and decodes it into the 7-segment outputs.

Wiring Steps

  1. Place the 7-segment display on your breadboard straddling the center gap.
  2. Connect the Common pin to GND (for common cathode).
  3. Connect each segment pin (a-g) through a 330 Ω resistor to the corresponding output on the decoder IC.
  4. Set your inputs (A, B, C, D) using switches on the digital trainer.

Conclusion Questions

Answer the following based on your laboratory experience.