RS485 serial communication, passing multiple values

Projects Programming
1

Hi Guys,

I am very new to coding with Arduino and I am experimenting with sending multiple ints from an Uno to a nano.

Backstory I'm trying to create a rov with two joysticks and an Uno at the top of a 20M cable and parsing those values onto a nano with a servo and a few escs at the bottom. using two max485 boards

I have been able to send one value of a pot down the link using the code below but I am struggling to understand how to send and receive two or more.

Any help would be appreciated

master.ino (556 Bytes)

slave.ino (965 Bytes)

2

looks like you're sending an integer value as an ascii string (e.g "123"), 3 ascii characters vs a single 8-bit byte, 0x7b.

parseInt() reads a number of ascii decimal digit characters ('0' - '9') and returns a values after a timeout period expires.

the timeout is on way to delimit a message. Another approach is to recognize a line termination chars (e.g. linefeed '\n')

you could format an ascii string with multiple values separated with a space and terminated, read an ascii string up to the line terminated and then translate the values in the string to two integer values using sscanf()

// ---------------------------------------------------------
void
setup (void)
{
    Serial.begin (9600);
}

// ---------------------------------------------------------
void
process (
    int  a,
    int  b )
{
    Serial.print   (__func__);
    Serial.print   (" ");
    Serial.print   (a);
    Serial.print   (" ");
    Serial.println (b);
}

// ---------------------------------------------------------
void
loop (void)
{
    static char s [80];
    static int  idx = 0;

    while (Serial.available ())  {
        char c = Serial.read ();
        s [idx++] = c;

        if ('\n' == c)  {
            s [idx] = 0;
            idx = 0;

            int a, b;
            sscanf (s, "%d %d", &a, & b);

            process (a, b);
        }
    }
}
3

You can use SerialTransfer.h to automatically packetize and parse your data for inter-Arduino communication without the headace. The library is installable through the Arduino IDE and includes many examples.

Here are the library's features:

This library:

  • can be downloaded via the Arduino IDE's Libraries Manager (search "SerialTransfer.h")
  • works with "software-serial" libraries
  • is non blocking
  • uses packet delimiters
  • uses consistent overhead byte stuffing
  • uses CRC-8 (Polynomial 0x9B with lookup table)
  • allows the use of dynamically sized packets (packets can have payload lengths anywhere from 1 to 254 bytes)
  • can transfer bytes, ints, floats, and even structs!!

Example TX Arduino Sketch:

#include "SerialTransfer.h"

SerialTransfer myTransfer;

void setup()
{
  Serial.begin(115200);
  Serial1.begin(115200);
  myTransfer.begin(Serial1);
}

void loop()
{
  char buff[] = "hi";

  myTransfer.txObj(buff, sizeof(buff));
  myTransfer.sendData(sizeof(buff));
  delay(100);
}

Example RX Arduino Sketch:

#include "SerialTransfer.h"

SerialTransfer myTransfer;

void setup()
{
  Serial.begin(115200);
  Serial1.begin(115200);
  myTransfer.begin(Serial1);
}

void loop()
{
  if(myTransfer.available())
  {
    char buff[40];
    
    myTransfer.rxObj(buff, sizeof(buff));
    
    Serial.println("New Data: ");
    Serial.write(buff, sizeof(buff));
    Serial.println();
  }
  else if(myTransfer.status < 0)
  {
    Serial.print("ERROR: ");

    if(myTransfer.status == -1)
      Serial.println(F("CRC_ERROR"));
    else if(myTransfer.status == -2)
      Serial.println(F("PAYLOAD_ERROR"));
    else if(myTransfer.status == -3)
      Serial.println(F("STOP_BYTE_ERROR"));
  }
}

For theory behind robust serial communication, check out the tutorials Serial Input Basics and Serial Input Advanced.