Introduction

DIY electronics projects are a great way to learn about circuit design and the use of integrated components. One interesting component to work with is the TD62503PG, a 7-channel Darlington sink driver IC, which is particularly useful for controlling multiple LEDs, relays, and other devices that require current amplification. In this article, we will explore how to build a multiplexed LED display driver using the TD62503PG, discussing its features, circuit design, assembly, and practical applications.

Understanding the TD62503PG Darlington Array

The TD62503PG is a high-voltage, high-current Darlington transistor array. It has seven open-collector outputs, meaning it can sink current from seven different outputs simultaneously. This makes it perfect for driving high-current loads like LEDs, relays, solenoids, or even motors. The TD62503PG is particularly advantageous for DIY projects that require efficient control of multiple loads with minimal power consumption from the control circuitry.

Key Features of the TD62503PG

1. Seven Darlington Pair Outputs: The TD62503PG provides seven independent channels that can sink current, making it suitable for driving LEDs or other loads in a multiplexed configuration.

2. High Output Current: Each channel can sink up to 500mA, allowing it to drive multiple LEDs or other components that require higher currents.

3. Open-Collector Outputs: The IC's outputs can be connected to loads with different supply voltages, providing flexibility in circuit design.

4. Integrated Flyback Diodes: The IC includes built-in protection diodes for driving inductive loads like relays or motors, protecting the circuit from back-emf.

5. Wide Operating Voltage Range: It can operate with voltages up to 50V, making it suitable for a variety of applications, including automotive systems.

The DIY Project: Building a Multiplexed LED Display Driver

In this project, we’ll use the TD62503PG to build a multiplexed LED display driver. This project will help you understand how to control multiple LEDs efficiently, a technique used in various electronic displays like seven-segment displays, dot-matrix displays, or even custom LED arrangements.

Components Required

· 1 x TD62503PG Darlington Array IC

· 1 x Arduino (e.g., Arduino Uno)

· 16 x LEDs (any color)

· 16 x Resistors (330Ω for LED current limiting)

· 4 x 7-segment displays (common anode type)

· Jumper wires

· Breadboard or PCB for assembly

· Power supply (5V for Arduino and LED display)

Circuit Design and Configuration

To efficiently control multiple LEDs, the TD62503PG is used as a current sink driver, allowing us to manage the ground side of the LEDs or segments of a seven-segment display. The Arduino will control which segments light up by sending signals to the TD62503PG.

The configuration will involve multiplexing: turning on one segment of the display at a time but doing so quickly enough that it appears all segments are on simultaneously. Multiplexing reduces the number of microcontroller pins required and lowers the overall power consumption.

Step 1: Understanding the Circuit Configuration

We will use the TD62503PG to control four 7-segment displays:

· Arduino Pins: Connected to the input pins of the TD62503PG (IN1 to IN7).

· TD62503PG Outputs: Connected to the cathodes of each segment in the 7-segment displays (A, B, C, D, E, F, G).

· Anode Control: The common anode of each display will be connected through a transistor or directly to the Arduino to control which display is active.

Step 2: Circuit Design

Arduino and TD62503PG Connections:

o Connect the input pins (IN1 to IN7) of the TD62503PG to digital pins on the Arduino.

o Connect the output pins (OUT1 to OUT7) to the cathodes of each LED segment of the displays.

Power Supply and Ground:

o Ensure the TD62503PG’s ground pin is connected to the common ground of the Arduino and power supply.

o Connect the VCC pin of the Arduino to the 5V rail.

Transistor Control (Optional):

o If you’re using more than one display, you can connect the common anode of each display to the collector of an NPN transistor (like 2N2222), with the emitter grounded.

o The base of each transistor is connected to a separate digital pin on the Arduino through a 1kΩ resistor. This allows the Arduino to turn each display on or off by controlling the base signal of each transistor.

Resistors for LEDs:

o Place 330Ω resistors between each segment pin of the display and the TD62503PG outputs to limit current and protect the LEDs.

Step 3: Assembly on a Breadboard

Set Up the Displays:

o Place the four 7-segment displays on the breadboard. Make sure they are oriented correctly for consistent wiring.

Connect the TD62503PG:

o Place the TD62503PG on the breadboard and connect its input pins to the Arduino.

o Connect its output pins to the cathodes of the 7-segment displays through current-limiting resistors.

Wire the Power Supply:

o Connect the 5V and GND rails on the breadboard to the Arduino’s 5V and GND pins.

Transistor Setup:

o If using transistors for anode control, connect them as described above.

Step 4: Writing the Arduino Code

The code for the Arduino will control the display by multiplexing the digits. It will activate each display one at a time and set the segments to show a number. This will create the illusion of all the displays being on at once when done rapidly.

cpp

// Arduino pins connected to the TD62503PG inputsconst int segmentPins[7] = {2, 3, 4, 5, 6, 7, 8};// Arduino pins connected to the transistors (for common anodes)const int digitPins[4] = {9, 10, 11, 12};

// Segment data for numbers 0-9const byte segmentData[10] = {

  B00111111, // 0

  B00000110, // 1

  B01011011, // 2

  B01001111, // 3

  B01100110, // 4

  B01101101, // 5

  B01111101, // 6

  B00000111, // 7

  B01111111, // 8

  B01101111 // 9

};

void setup() {

  // Set up segment and digit pins as outputs

  for (int i = 0; i < 7; i++) {

    pinMode(segmentPins[i], OUTPUT);

  }

  for (int i = 0; i < 4; i++) {

    pinMode(digitPins[i], OUTPUT);

  }

}

void loop() {

  for (int digit = 0; digit < 4; digit++) {

    displayDigit(digit, digit); // For demonstration, display the same digit number as the position

    delay(5); // Short delay for multiplexing

  }

}

// Function to display a digit on a specific displayvoid displayDigit(int digitIndex, int number) {

  // Turn off all digits

  for (int i = 0; i < 4; i++) {

    digitalWrite(digitPins[i], LOW);

  }

  // Set the segments for the number

  byte segments = segmentData[number];

  for (int i = 0; i < 7; i++) {

    digitalWrite(segmentPins[i], (segments >> i) & 1);

  }

  // Turn on the desired digit

  digitalWrite(digitPins[digitIndex], HIGH);

}

Explanation of the Code

1. Pin Setup: We configure the Arduino pins connected to the TD62503PG as output pins.

2. Multiplexing Control: The displayDigit function controls which display is active and sets the segments for the number.

3. Loop Function: The main loop cycles through each display, showing the appropriate number. The delay creates the effect of all displays being active simultaneously.

Testing and Troubleshooting

No Display Output:

o Check all connections, especially the power and ground connections for the TD62503PG and Arduino.

o Ensure the LEDs and resistors are connected correctly.

Flickering Display:

o Reduce the delay time in the multiplexing loop to speed up the refresh rate.

o Verify that the transistors (if used) are correctly connected.

Incorrect Digits:

o Double-check the segmentData array and ensure the segments are wired correctly to the TD62503PG outputs.

Applications of the TD62503PG Multiplexed Display Circuit

The multiplexed LED display circuit we’ve built has several practical applications:

1. Digital Clocks: Use the display driver to show hours, minutes, and seconds on a 7-segment display.

2. Counter Displays: Implement a counter for game scores, events, or production lines.

3. Temperature and Sensor Readouts: Display data from sensors (e.g., temperature or pressure) in real-time.

4. Frequency Display: Use the display to show the frequency of an input signal in a frequency meter application.

Advanced Enhancements

Once the basic multiplexed display is functioning, consider adding advanced features:

1. Rotary Encoder Input: Add a rotary encoder to control the displayed value for interactive projects.

2. Bluetooth Integration: Use a Bluetooth module to send data from a smartphone to the Arduino, displaying text or numbers remotely.

3. Custom Animations: Create visual effects or animations for decorative displays or interactive exhibits.

4. Sensor Integration: Connect environmental sensors like temperature or humidity sensors to display real-time data.

Conclusion

Building a multiplexed LED display driver with the TD62503PG is an engaging and educational DIY project that highlights the power and versatility of Darlington arrays. Whether you’re interested in building a digital clock, a counter, or sensor-based displays, this project offers a solid foundation for further exploration into electronics and digital control systems. Experiment with different configurations and enhancements, and let your creativity drive new applications!