RS485 Communication Issue: Garbage Values on OLED Display

Question

Hello Stack Exchange community,

I am currently working on a project involving two Arduino Nano boards connected via RS485 communication using MAX485 chips. I have set up the connections between the Arduinos as per the figure provided. Additionally, I have included the master and slave code for reference.

Connections:

Arduino UNO =>RS485 Module 5V =>VCC; GND =>GND; pin 0 (RX) => RO; pin 8 => RE & DE; pin 1 (TX)=> DI;

Code:

Master Code:

arduino

int Enable_pin = 8;

void setup()
{
  Serial.begin(9600);
  pinMode(Enable_pin, OUTPUT);

  digitalWrite(Enable_pin, HIGH);
}
void loop()
{
  for(uint8_t i =0;i<=99;i++)
  {Serial.println(i);
  delay(1000);}
}

Slave Code:

arduino

#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

int Enable_pin = 8;

Adafruit_SSD1306 display = Adafruit_SSD1306(128, 64, &Wire, -1);

void setup()
{
  Serial.begin(9600);
  pinMode(Enable_pin, OUTPUT);
  digitalWrite(Enable_pin, LOW);        //  (LOW to receive value from Master)
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.display();
  delay(100);
  display.clearDisplay();
  display.display();
  display.setTextColor(WHITE);

}

void loop()

{
  while (Serial.available())
  {

    display.clearDisplay();
    uint8_t PWM_master = Serial.read();            //Receive INT value from Master throught RS-485
    
 

    display.setCursor(50, 30);
    display.setTextSize(4);
    display.print(PWM_master);

    display.display();
    delay(100);

  }

The expected output of the system is continuous numbers from 0 to 99 displayed on an OLED screen. However, I am encountering an issue where I am receiving garbage values intermittently on the OLED display. Specifically, the garbage values are either '10' or '13'. This is puzzling as my RS485 module wires are short, and the environment is not noisy. Additionally, I am powering the setup using a laptop's USB output.

I am seeking assistance in understanding why these consistent garbage values (10 or 13) are appearing in the output. Could it be related to the code, hardware connections, or power supply? Any insights or suggestions to resolve this issue would be greatly appreciated.

Thank you in advance for your help!

Answer 1

You are printing variable as text line, so the 13 and 10 are the Carrige Return and Line Feed character byte values.

So you are sending the data as line of ASCII text string, so for example the value 45 is sent as characters '4', '5', 13, 10.

Which means when you are reading those as bytes you get a stream of bytes 52, 53, 13, 10.

Also the next thing that will go wrong is that you like many others think RS-485 is a two wire interface. Well it is but it needs a common ground between the transceivers. So unless you provide a common ground reference, such as a third ground wire between devices if no other ground reference is available, it will stop working if you use two separate floating mains power supplies.

Answer 2

I changed my master code to following and it fixed the problem.

int Enable_pin = 8;

void setup()
{
  Serial.begin(9600);
  pinMode(Enable_pin, OUTPUT);

  digitalWrite(Enable_pin, HIGH);
}
void loop()
{
  for(uint8_t i =0;i<=99;i++)
  {Serial.print(char(i));
  delay(1000);}
}