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Converting Binary to 7-Segment Displays with the SN74LS47N

Converting Binary to 7-Segment Displays with the SN74LS47N


The SN74LS47N is a popular 7-segment decoder chip that can convert binary inputs into outputs suitable for driving common cathode 7-segment LED or LCD displays. With just a single chip, you can easily create a binary-to-decimal converter for decimal digit display or other simple numeric displays.

How the SN74LS47N Works

The SN74LS47N contains combinatorial logic that converts 4-bit binary coded decimal (BCD) inputs into 7 outputs that can drive the segments of a 7-segment display.

The logic works as follows:

  • It has 4 binary inputs labeled A, B, C, and D
  • Depending on the logic level on these inputs, 1 of the 7 outputs will be enabled
  • This lights up the corresponding segment of the display

For example, applying the BCD code for the number 5 (0101) to the inputs would enable the “e” segment output. Applying the code for 3 (0011) would enable the “d” segment.

The SN74LS47N handles all the logic necessary to convert any valid 4-bit BCD number to its 7-segment equivalent.

Wiring the SN74LS47N to a 7-Segment Display

To use the SN74LS47N, you simply need to:

  1. Connect the 4 BCD inputs to 4 digital outputs from your microcontroller or logic circuits
  2. Connect the 7 segment outputs to the corresponding pins on the common cathode 7-segment display
  3. Connect the ground of the SN74LS47N to the common cathode pin on the display

Here is a sample wiring diagram:

SN74LS47N7-Segment Display
dDecimal Point
eCommon Cathode

Sample Code

Here is some sample Arduino code to demonstrate how to use the SN74LS47N to display the number 5:


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// SN74LS47N connected to Arduino pins 2-5 // 7-segment display pins connected according to wiring diagram void setup() { // Set Arduino pins 2-5 as outputs pinMode(2, OUTPUT); pinMode(3, OUTPUT); pinMode(4, OUTPUT); pinMode(5, OUTPUT); } void loop() { // Display number 5 (binary 0101) digitalWrite(2, LOW); digitalWrite(3, HIGH); digitalWrite(4, LOW); digitalWrite(5, HIGH); delay(1000); // Wait 1 second }

This simply sets the correct BCD inputs to show the number 5 on the display. You can expand on this to display different values.

Common Questions

What display types can I use with the SN74LS47N?

The SN74LS47N is compatible with common cathode 7-segment LED and LCD displays. It will not work directly with common anode displays.

What is the maximum frequency I can run the SN74LS47N at?

The SN74LS47N can operate at frequencies up to 15MHz, making it compatible with many microcontrollers.

Do I need any other components besides the SN74LS47N and display?

You may need current-limiting resistors for each segment output if using an LED display. Refer to the display datasheet for appropriate resistor values.

What logic voltage levels does the SN74LS47N need?

The SN74LS47N uses standard 5V TTL logic levels. For 3.3V systems, a logic level shifter will be required.

This covers the basics of using the versatile SN74LS47N 7-segment decoder chip to convert binary inputs into drive signals for 7-segment displays. With just this simple component, you can create easy numeric displays for counters, clocks, and other projects.