How to Use HCMS-291x/297x 8-Character Serial LED Display: Examples, Pinouts, and Specs

The HCMS-291x/297x is a compact, serially interfaced LED display module manufactured by Broadcom. It is capable of displaying up to 8 alphanumeric characters, making it ideal for applications requiring clear and concise text output in a small form factor. This module integrates LED characters, drivers, and a shift register into a single package, simplifying design and reducing component count.

• Industrial control panels
• Consumer electronics
• Test and measurement equipment
• Communication devices
• Embedded systems requiring alphanumeric displays

The HCMS-291x/297x series offers a range of features and specifications that make it versatile for various applications. Below are the key technical details:

The HCMS-291x/297x module has a 14-pin configuration. Below is the pinout and description:

The HCMS-291x/297x is designed for ease of use in embedded systems. Below are the steps and considerations for integrating this module into your circuit:

1. Power Supply: Connect the Vcc pin to a 5V power source and the GND pin to ground.
2. Serial Interface:
   • Connect the DATA IN pin to the microcontroller's MOSI (Master Out Slave In) pin.
   • Connect the CLK pin to the microcontroller's SPI clock pin.
   • Connect the LOAD/CS pin to a GPIO pin configured as chip select.
3. Reset: Connect the RESET pin to a GPIO pin or tie it to Vcc for normal operation.
4. Cascading Modules: If using multiple modules, connect the DATA OUT pin of the first module to the DATA IN pin of the next module.

Below is an example of how to interface the HCMS-291x/297x with an Arduino UNO:

#include <SPI.h>

// Pin definitions
#define LOAD_PIN 10  // Chip select pin
#define RESET_PIN 9  // Reset pin

void setup() {
  pinMode(LOAD_PIN, OUTPUT);
  pinMode(RESET_PIN, OUTPUT);

  // Initialize SPI
  SPI.begin();
  SPI.setClockDivider(SPI_CLOCK_DIV16); // Set SPI clock speed
  SPI.setDataMode(SPI_MODE0);           // Set SPI mode
  SPI.setBitOrder(MSBFIRST);            // Send most significant bit first

  // Reset the display
  digitalWrite(RESET_PIN, LOW);
  delay(10);
  digitalWrite(RESET_PIN, HIGH);

  // Initialize the display
  digitalWrite(LOAD_PIN, LOW);
  sendData(0x01); // Example command to clear the display
  digitalWrite(LOAD_PIN, HIGH);
}

void loop() {
  // Display "HELLO" on the module
  digitalWrite(LOAD_PIN, LOW);
  sendData(0x48); // ASCII for 'H'
  sendData(0x45); // ASCII for 'E'
  sendData(0x4C); // ASCII for 'L'
  sendData(0x4C); // ASCII for 'L'
  sendData(0x4F); // ASCII for 'O'
  digitalWrite(LOAD_PIN, HIGH);

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

// Function to send data to the display
void sendData(byte data) {
  SPI.transfer(data);
}

• Power Supply: Ensure a stable 5V power supply to avoid flickering or malfunction.
• Reset Signal: Always reset the module during initialization to ensure proper operation.
• SPI Configuration: Use SPI mode 0 and MSB-first data order for compatibility.
• Cascading: When cascading multiple modules, ensure proper data flow by connecting DATA OUT to DATA IN of the next module.

1. Display Not Working:

   • Check the power supply connections (Vcc and GND).
   • Verify the SPI connections and configuration.
   • Ensure the RESET pin is properly initialized.

2. Incorrect Characters Displayed:

   • Verify the data being sent matches the ASCII character set.
   • Check for timing issues in the SPI communication.

3. Flickering Display:

   • Ensure the power supply can handle the current requirements.
   • Check for loose connections or poor soldering.

• Use decoupling capacitors (e.g., 0.1 µF) near the Vcc pin to stabilize the power supply.
• If cascading modules, ensure the clock and data signals are not degraded over long distances.
• Test the module with a simple program to verify functionality before integrating it into a complex system.

Q: Can I use this module with a 3.3V microcontroller?
A: The HCMS-291x/297x requires a 5V power supply. Use level shifters for 3.3V microcontrollers.

Q: How many modules can I cascade?
A: The number of modules depends on the driving capability of your microcontroller and the SPI clock speed. Typically, up to 4-6 modules can be cascaded without significant signal degradation.

Q: Is the module compatible with I2C?
A: No, the HCMS-291x/297x uses an SPI-compatible serial interface.

This concludes the documentation for the HCMS-291x/297x 8-Character Serial LED Display.