Unable to tell if error is from receiving or transmitting end

Question

so I am having trouble sending data using software serial's write function.

TX Code:

#include <SoftwareSerial.h>

SoftwareSerial TX(2,3); 

void setup() { 
  // put your setup code here, to run once: 
  TX.begin(1200); 
} 

void loop() { 
    TX.write(60);  
}

Is the delay necessary?

RX Code:

#include <SoftwareSerial.h>
SoftwareSerial RX(2,3); //(rx pin, tx pin)
const unsigned int bufferSize = 100;

void setup() { 
  Serial.begin(9600); 
  RX.begin(1200); 

}

void printBuffer(const uint8_t *serialBuffer)
{
  //print contents of buffer
  for (int i = 0; i<100; i++) 
    Serial.println(serialBuffer[i], BIN);
}

void processBytes(const uint8_t value)
{ 
  static uint8_t serialBuffer[bufferSize]; //buffer to hold values
  static unsigned int startPosition=0;

  if(startPosition < bufferSize)
    serialBuffer[startPosition++] = value; 

  else
  {
    printBuffer(serialBuffer);
    startPosition = 0;
  }

}//end of processBytes
void loop() { 

  //check if data is available in serial buffer
  while(RX.available())
  {
    //process data
    processBytes(RX.read());
  }   
}

If i transmit the number 60, it prints 226 constantly for 2-3 seconds, then prints 60 for a short while, then goes back to printing 226. Am I doing something wrong with my code?

FIRST QUESTION: In the case when startPosition (in the process function) equals 100, it will call print. Print will then print 100 integers. Now, when doing that, there could still be data being transmitted from the transmitter. But the read function won't be executed until printBuffer returns, process returns, and the while loop iterates again. So during that time, couldn't some transmitted values potentially not be read?

SECOND QUESTION How come Software serial doesn't synchronize incorrectly more often? How is it being so accurate if the start bit is just a single bit and it's a 0. So for instance, if payload has some 0s, how come one of those 0s aren't being assumed to be the startbit? How does this get resolved? I looked at the software serial library, but I am not able to find out why. Any guidance here?

THIRD QUESTION Other than getting the startbit syncing right, are there other ways to sync the data? I was reading of NRZ encoding, manchester encoding, etc. Can any of these be implemented here? Also, would it be wise to alter the softwareSerial library to have more than one startbit?

Any guidance would be very appreciated! Thank you so much! This is all being done with wireless RF modules.

Nick Gammon · Accepted Answer · 2015-10-23T20:38:45.633

void loop() { 
  Serial.println("NEW-------------");
  int x;
  int y[100];
  for(int i = 0; i<100; i++){ 
    x=RX.read(); 
    y[i] = x;
  } 
...
}

You are reading data without checking if there is any data there. That's like watching the TV without checking if it is turned on. Of course you get weird data.

SoftwareSerial RX(0,1); //(rx pin, tx pin)

Pins 0 and 1 are used by HardwareSerial. Why are you using them for SoftwareSerial?

SoftwareSerial RX(0,1); //(rx pin, tx pin)
...

  Serial.begin(9600); 
  RX.begin(1200);

So you initialized HardwareSerial, which now controls pins 0 and 1.

Then you try to initialize SoftwareSerial on those same pins! Would you mind explaining why?

Whatever your explanation is, it won't work.

I've added in the changes you mentioned, but the data still seems to be skewed.

You've changed things, for sure:

 for(int i = 0; i<100; i++){ 
    if(RX.available())
      x=RX.read(); 

    y[i] = x;
    }

Let's see. In a loop of 100 iterations you see if anything is available (and if so, put it into x).

Then, regardless of whether or not you got anything you now assign x to y[i]. So, most of the time, y[i] will have garbage in it.

the data still seems to be skewed

Not surprised. Do it differently. Only write to the array if you have data. In fact you may want a complete rework. Read this:

How to read serial without blocking

I have posted the amended code. Change: Only add to the array is data is being read from buffer.

  int y[100];
  for(int i = 0; i<100; i++){ 
    if(RX.available())
    {
      x=RX.read(); 
      y[i] = x;
    }
  } 

 for (int j = 1; j<=64; j++){ 
    Serial.println(y[j]);
  }

You still have not fixed it. Let me talk you through what it is doing now.

You are making 100 attempts to read some data. One or two may succeed, and they will be put into the buffer y (funny name for a buffer, right?).

So imagine . is garbage and X is good data, after doing that loop of 100 the buffer will look like this:

........X...........X...........X...X......................X.............................................

So your buffer is still 80% unchanged garbage. Then you print the first 64 elements (why 64 and not 100?) and you get a lot of garbage out. Exactly as expected.

You need to think about what you are doing. Draw it out on a bit of paper, perhaps.

Here is some example code from the page I linked for you, more than once. Please compare:

// how much serial data we expect before a newline
const unsigned int MAX_INPUT = 50;

void setup ()
  {
  Serial.begin (115200);
  } // end of setup

// here to process incoming serial data after a terminator received
void process_data (const char * data)
  {
  // for now just display it
  // (but you could compare it to some value, convert to an integer, etc.)
  Serial.println (data);
  }  // end of process_data

void processIncomingByte (const byte inByte)
  {
  static char input_line [MAX_INPUT];
  static unsigned int input_pos = 0;

  switch (inByte)
    {

    case '\n':   // end of text
      input_line [input_pos] = 0;  // terminating null byte

      // terminator reached! process input_line here ...
      process_data (input_line);

      // reset buffer for next time
      input_pos = 0;  
      break;

    case '\r':   // discard carriage return
      break;

    default:
      // keep adding if not full ... allow for terminating null byte
      if (input_pos < (MAX_INPUT - 1))
        input_line [input_pos++] = inByte;
      break;

    }  // end of switch

  } // end of processIncomingByte  

void loop()
  {
  // if serial data available, process it
  while (Serial.available () > 0)
    processIncomingByte (Serial.read ());

  // do other stuff here like testing digital input (button presses) ...

  }  // end of loop

Unable to tell if error is from receiving or transmitting end

1 Answers1

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