lamaPLC: DM56A04 / DM36B06 digital tube display with Modbus Communication

• Working voltage: DC 5 - 28V
• Working current: 4.3 - 42mA (related to the brightness of the digital tube)
• MODBUS RTU protocol, 03 read command, 06 or 16 write command.
• Device address: 1~247, default 1, by modifying the 485 address, up to 247 modules can be used in cascade (more than 32, please use RS485 repeater)
• Digital tube color: red
• Digital tube tube digits: 6 digits 0.36 inches / 4 digits 0.56 inches
• Communication interface: RS-485 (Modbus RTU)
• Function: It can display numbers, ASCII characters, letters, floating-point numbers, negative numbers, etc., and the brightness can be adjusted; it supports electronic label function, and the initial display content can be set after power-on
• Supported baud rates: 1200 2400 4800 9600 (default) 19200 38400 57600 115200,

Modbus connection characteristics:
Default Modbus settings: 9600 baud, 8N1, RTU communication, slave ID: 1
Function Code: 06/16 control, 03 read status

To use these displays with an Arduino, you need an RS-485 to TTL converter module (like a MAX485 module) to translate the signals. You'll also use the Modbus library to send commands.

• Arduino Board (e.g., Arduino Uno, Nano)
• DM56A04 or DM36B06 display (4-digit and 6-digit variants, respectively)
• RS-485 to TTL Converter Module (e.g., a board with a MAX485 chip)
• External 5V to 24V DC Power Supply for the display module (Arduino's 5V pin may not be enough)
• Jumper Wires

Connect the components as follows, using the Arduino's hardware serial pins (Pin 0/RX and Pin 1/TX):

Note: The RE and DE pins on the MAX485 module should be connected together and wired to a single digital pin (e.g., Pin 2) to control data direction (send/receive).

Install the ModbusMaster library by Doc Walker through the Arduino IDE Library Manager. This library simplifies Modbus RTU communication.

This code uses the ModbusMaster library to send a simple “display value” command (Function Code 6) to the display's default address (0x01).

#include <ModbusMaster.h>
 
// Initialize ModbusMaster instance
// Use Hardware Serial on pins 0 (RX) and 1 (TX)
ModbusMaster node;
 
#define DE_RE_PIN 2 // Pin to control RS-485 direction
 
void setup() {
  Serial.begin(9600); // Start serial communication
  node.begin(1, Serial); // Slave ID 1, use the standard Serial port
 
  // Set the direction control pin
  pinMode(DE_RE_PIN, OUTPUT);
  node.setTransmitBuffer(DE_RE_PIN); // Tell the library which pin controls direction
}
 
void loop() {
  static uint16_t value_to_display = 0;
  uint8_t result;
 
  // Send Modbus command to display the value
  // Function 0x06 (Write Single Register)
  // Address 0x0000 (usually the register for the main value)
  // Value to display
  result = node.writeSingleRegister(0x0000, value_to_display);
 
  if (result == node.ku8MBSuccess) {
    // Command sent successfully
    value_to_display++;
    if (value_to_display > 9999) { // Adjust max value based on 4 or 6 digits
      value_to_display = 0;
    }
  } else {
    // Handle communication error (optional)
    // Serial.print("Error: ");
    // Serial.println(result);
  }
 
  delay(1000); // Update every second
}

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