BCD to 7-Segment Display

Build a decimal number display using the SN74LS47 BCD decoder and a 7-segment LED display—convert binary to human-readable digits!

Overview

While binary LEDs are useful for learning, reading binary numbers quickly is difficult. The SN74LS47 BCD (Binary Coded Decimal) decoder converts a 4-bit binary input into the signals needed to display digits 0-9 on a 7-segment display. This is the same technology used in digital clocks, meters, and countless other displays!

Components Needed

  • 1x SN74LS47 IC
  • 1x 5611BH 7-segment display
  • 1x 10kΩ resistor
  • severalx Wires
  • 1x Breadboard

Instructions

  1. Gather Your Components

    Collect the SN74LS47 BCD decoder IC, a 5611BH common-anode 7-segment display, a 10kΩ resistor, wires, breadboard, and 5V power supply.

  2. Identify the SN74LS47

    The SN74LS47 is a 16-pin IC. Pins 7, 1, 2, 6 are BCD inputs (A, B, C, D). Pins 9-15 are segment outputs (a-g). Pin 8 is ground, pin 16 is VCC. Additional pins control blanking and lamp test.

  3. Wire the Display Circuit

    Connect the 74LS47: pin 16 to 5V, pin 8 to ground. Connect segment outputs (a-g) to the corresponding display pins. The display's common anode connects to 5V through the resistor. Connect your 4-bit input source to pins A, B, C, D.

  4. Test: Display Digits 0-9

    Connect to a 4-bit adder or switch tool and cycle through inputs 0000 to 1001. You should see digits 0 through 9 displayed clearly.

  5. Special Characters (Inputs 10-15)

    BCD inputs above 9 (1010-1111) produce special characters since they're outside the decimal range. These can be useful for error indication or special symbols.

Challenges

  • Build a two-digit display for numbers 0-99
  • Add a decimal point for displaying values like 3.7
  • Create a simple counter using a 555 timer and decade counter
  • Design a digital thermometer readout using this display