How to Use 74LS47N: Examples, Pinouts, and Specs

The SN74LS47N, manufactured by Texas Instruments, is a BCD (Binary-Coded Decimal) to 7-segment decoder/driver IC. This component is designed to convert a 4-bit BCD input into the corresponding segment control signals required to display numbers 0-9 on a 7-segment display. It is widely used in digital clocks, calculators, and other devices that require numerical displays.

1. Power Supply: Connect pin 16 (VCC) to a 5V power supply and pin 8 (GND) to ground.
2. BCD Inputs: Connect the BCD inputs (pins 1, 2, 3, and 4) to the digital outputs of a microcontroller or other digital logic source.
3. 7-Segment Display: Connect the segment outputs (pins 5, 6, 7, 9, 10, 11, and 12) to the corresponding segments of a common-anode 7-segment display.
4. Control Pins:
   • Connect pin 13 (LT) to VCC if the lamp test function is not needed.
   • Connect pin 14 (BI/RBO) to VCC if blanking is not required.
   • Connect pin 15 (RBI) to VCC if ripple blanking is not required.

• Ensure that the power supply voltage is within the specified range (4.75V to 5.25V).
• Use current-limiting resistors for each segment to prevent excessive current draw.
• Avoid leaving unused inputs floating; connect them to a defined logic level (either VCC or GND).

// Arduino UNO to SN74LS47N BCD to 7-Segment Display Example

// Define BCD input pins
const int bcdA = 2;
const int bcdB = 3;
const int bcdC = 4;
const int bcdD = 5;

// Number to display (0-9)
int number = 0;

void setup() {
  // Set BCD pins as outputs
  pinMode(bcdA, OUTPUT);
  pinMode(bcdB, OUTPUT);
  pinMode(bcdC, OUTPUT);
  pinMode(bcdD, OUTPUT);
}

void loop() {
  // Display the number on the 7-segment display
  displayNumber(number);

  // Increment the number
  number++;
  if (number > 9) {
    number = 0;
  }

  // Wait for 1 second
  delay(1000);
}

void displayNumber(int num) {
  // Convert the number to BCD and set the pins
  digitalWrite(bcdA, num & 0x01);
  digitalWrite(bcdB, (num >> 1) & 0x01);
  digitalWrite(bcdC, (num >> 2) & 0x01);
  digitalWrite(bcdD, (num >> 3) & 0x01);
}

1. No Display Output:

   • Ensure that the power supply is connected and providing the correct voltage.
   • Check all connections to the 7-segment display and the SN74LS47N.
   • Verify that the BCD inputs are receiving the correct signals.

2. Incorrect Digits Displayed:

   • Ensure that the BCD inputs are correctly connected and providing the correct binary values.
   • Check for any loose or incorrect connections.

3. Dim or Flickering Segments:

   • Verify that the current-limiting resistors are of the correct value.
   • Ensure that the power supply can provide sufficient current for the display.

• Use a Multimeter: Check the voltage levels at various points in the circuit to ensure they are within the expected range.
• Check Connections: Double-check all wiring and connections to ensure they are secure and correct.
• Test Individual Components: If possible, test the 7-segment display and the SN74LS47N separately to isolate the issue.

Q: Can the SN74LS47N drive a common-cathode 7-segment display? A: No, the SN74LS47N is designed to drive common-anode 7-segment displays.

Q: What is the purpose of the LT, BI/RBO, and RBI pins? A:

• LT (Lamp Test) is used to test all segments by lighting them up when pulled low.
• BI/RBO (Blanking Input/Ripple Blanking Output) is used to blank the display or cascade multiple decoders.
• RBI (Ripple Blanking Input) is used to blank leading zeros in multi-digit displays.

Q: Can I use the SN74LS47N with a 3.3V microcontroller? A: The SN74LS47N is designed for a 5V supply. Using it with a 3.3V microcontroller may require level shifters to ensure proper operation.

This documentation provides a comprehensive guide to using the SN74LS47N BCD to 7-segment decoder/driver IC. By following the instructions and best practices outlined, users can effectively integrate this component into their projects.