lamaPLC: TM1650 7-Segment Display with I²C like or Modbus Communication

The TM1650 is a popular, cost-effective integrated circuit (IC) used to drive 4-digit, 7-segment LED displays while minimizing the number of microcontroller I/O pins required.

The TM1650 7-segment display uses a proprietary 2-wire serial protocol that is very similar to I²C, but it is not a standard, addressable I²C device. It uses a clock (SCL) and a data line (SDA) to communicate with a microcontroller.

• LED Display Controller: Manages all multiplexing for a 4-digit display with optional decimal points.
• Key Scanning: It can also scan up to 4 keys/buttons.
• Simple Interface: Uses a 2-wire serial communication protocol that mimics the physical layer of I²C (SCL and SDA lines).
• Adjustable Brightness: Supports 8 intensity levels.
• Low Pin Count: Typically requires only VCC, GND, SCL, and SDA pins to operate.
• Modbus RTU: With TP8485E, it is an RS-485 communication transceiver

• VCC to 5V
• GND to GND
• SCL (Clock) to A5 (or the SCL pin)
• SDA (Data) to A4 (or the SDA pin)

#include <Wire.h>
#include <TM1650.h>
 
TM1650 d;
 
void setup() {
  Wire.begin();        // Start I²C communication
  d.init();            // Initialize the display
  d.displayOn();       // Turn display on
  d.setBrightness(4);  // Set brightness (0 to 7)
}
 
void loop() {
  // Display a fixed number
  d.displayString("1234");
  delay(2000);
 
  // Simple counter
  for (int i = 0; i <= 100; i++) {
    d.displayString(String(i).c_str());
    delay(100);
  }
}

Key Features

• Brightness Control: Use setBrightness(level) where level is 0–7.
• Display Modes: The TM1650 can operate in 8×4 or 7×4 display modes and supports keypress scanning, though some libraries focus primarily on the display output.
• Individual Digits: Use setDot(digit, true) to enable decimal points for specific digits.

The TP8485E is a robust RS-485 transceiver designed for industrial communication networks.

• Function: It converts standard Transistor-Transistor Logic (TTL) or CMOS logic signals from a microcontroller into differential signals (A and B lines) suitable for long-distance, noise-resistant serial communication over twisted-pair cables.
• Interface: It communicates with a microcontroller via standard UART (Universal Asynchronous Receiver/Transmitter) pins (TX/RX) and requires additional General Purpose Input/Output (GPIO) pins to control the driver/receiver enable (DE/RE) lines.
• Applications: Its primary uses are in industrial automation, HVAC systems, e-metering networks, and DMX512 lighting control, where reliable data transmission over long distances in noisy environments is essential.

Modbus connection characteristics:
Default Modbus settings: 9600 baud, 8N1, RTU communication, slave ID: 1

After powering up, a number, such as “0013”, flashes briefly. The first digit represents the slave ID (1), and the second indicates the baud rate (3: 9600).

The “write multiple registers” Modbus function (10) works, with three pieces of information (signal, number of digits, brightness) (2.468 / low brightness 1: TX 01 10 00 00 00 03 06 09 a4 00 03 00 01 a6 00)

The registers must be written one at a time using the “write single register” function (6). (Send 1234: TX: 01 06 00 00 04 d2 0b 57)

TP8485E (RS-485):

• RO (Receiver Out) to Arduino RX (Pin 0 or SoftwareSerial RX).
• DI (Driver In) to Arduino TX (Pin 1 or SoftwareSerial TX).
• RE & DE (Enable pins) tied together to a digital pin (e.g., Pin 2) to toggle between Receive (LOW) and Transmit (HIGH).

TM1650 (Display):

• SCL to A5 and SDA to A4 (standard I2C pins).

This sketch receives a 4-digit number over RS-485 and displays it on a 7-segment display. You will need the TM1650 library by Anatoli Arkhipenko.

#include <Wire.h>
#include <TM1650.h>
 
#define RS485_CONTROL_PIN 2  // Pin to toggle RE/DE on TP8485E
TM1650 d;
 
void setup() {
  // Initialize RS-485
  Serial.begin(9600);
  pinMode(RS485_CONTROL_PIN, OUTPUT);
  digitalWrite(RS485_CONTROL_PIN, LOW); // Set to RECEIVE mode initially
 
  // Initialize TM1650 Display
  Wire.begin();
  d.init();
  d.displayOn();
  d.setBrightness(4);
  d.displayString("WAIT");
}
 
void loop() {
  if (Serial.available() > 0) {
    // Read incoming string from RS-485 (e.g., "1234")
    String receivedData = Serial.readStringUntil('\n');
    receivedData.trim(); // Clean whitespace
 
    if (receivedData.length() > 0) {
      d.displayString(receivedData.c_str());
    }
  }
}
 
// Function to send data back via RS-485 if needed
void sendRS485(String msg) {
  digitalWrite(RS485_CONTROL_PIN, HIGH); // Switch to TRANSMIT mode
  Serial.println(msg);
  Serial.flush();                        // Ensure all data is sent
  digitalWrite(RS485_CONTROL_PIN, LOW);  // Switch back to RECEIVE mode
}

• Mode Toggling: For half-duplex chips like the TP8485E, you must set the DE/RE pins HIGH to send data and LOW to listen.
• Power Stability: TM1650 displays can be “noisy” on the 5V rail; adding a 100µF capacitor across VCC and GND near the display is highly recommended to prevent flickering.
• Addressing: If your RS-485 bus has multiple devices, you should implement a simple protocol (e.g., ID:DATA) so the Arduino displays only messages intended for it.

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