Need help with I2C Communication between RoboRio and Arduino

[aarondesuu]

I need help with communication between the roborio and an arduino board. Basically when my robot enters disabled mode, it calls the constructor of an arduino class which basically sends an I2C message.

package main.java.frc.utils;

import edu.wpi.first.wpilibj.I2C;

public class ArduinoI2C {
	public ArduinoI2C() {
		I2C arduino = new I2C(I2C.Port.kOnboard, 4);
		String WriteString = "test"; // "test" will be the message we will send to the arduino
		char[] CharArray = WriteString.toCharArray(); //Turns the message into an array
		byte[] WriteData = new byte[CharArray.length]; //Turns the array into a byte
		for (int i = 0; i < CharArray.length; i++) {
			WriteData[i] = (byte) CharArray[i];
		}
		arduino.transaction(WriteData, WriteData.length, null, 0); //Send the message "test" to the Arduino
	};
}

And when the Arduino receives the message, an LED lights up on the Arduino

#include <Wire.h>
#define LED_PIN 9
void setup() {
  pinMode(LED_PIN, OUTPUT);
  digitalWrite(LED_PIN, LOW);
  Wire.begin(4);                // join i2c bus with address #4
  Wire.onReceive(receiveEvent); // register event
}

void loop() {
  delay(100);
}

// function that executes whenever data is received from master
// this function is registered as an event, see setup()
void receiveEvent(int howMany)
{
  String LED = "";
 
  while ( Wire.available() > 0 )
  {
    char n=(char)Wire.read();
    if(((int)n)>((int)(' ')))
   LED += n; 
  }
  
  if (LED == "test") 
  {
    for(int x = 0; x<10; x++) {
    digitalWrite(LED_PIN, HIGH);
    delay(500);
    digitalWrite(LED_PIN, LOW);
    delay(500);
    }
  
    
  }
}

When I tested this, nothing happened. Can anyone tell me why? Any recommendations? something wrong with my code? (Note: I am not good with coding )**

[codedr]

The notes I have from implementing I2C was that sometimes you need a 10K pull up resistor on the SCL pin to 5v.

The picture on this page http://i2c.info/ shows a wiring diagram.

[Sky_Captain]

I’m at work atm, and don’t have my personal laptop, but I’ve gone through this, and I can post code that I knows works when I get home. I ran into this same issue when I was fooling with an Arduino and LEDs.

[gerthworm]

I need help with communication between the roborio and an arduino board. Basically when my robot enters disabled mode, it calls the constructor of an arduino class which basically sends an I2C message.

package main.java.frc.utils;

import edu.wpi.first.wpilibj.I2C;

public class ArduinoI2C {
	public ArduinoI2C() {
		I2C arduino = new I2C(I2C.Port.kOnboard, 4);
		String WriteString = "test"; // "test" will be the message we will send to the arduino
		char] CharArray = WriteString.toCharArray(); //Turns the message into an array
		byte] WriteData = new byte[CharArray.length]; //Turns the array into a byte
		for (int i = 0; i < CharArray.length; i++) {
			WriteData* = (byte) CharArray*;
		}
		arduino.transaction(WriteData, WriteData.length, null, 0); //Send the message "test" to the Arduino
	};
}

And when the Arduino receives the message, an LED lights up on the Arduino

#include <Wire.h>
#define LED_PIN 9
void setup() {
  pinMode(LED_PIN, OUTPUT);
  digitalWrite(LED_PIN, LOW);
  Wire.begin(4);                // join i2c bus with address #4
  Wire.onReceive(receiveEvent); // register event
}

void loop() {
  delay(100);
}

// function that executes whenever data is received from master
// this function is registered as an event, see setup()
void receiveEvent(int howMany)
{
  String LED = "";
 
  while ( Wire.available() > 0 )
  {
    char n=(char)Wire.read();
    if(((int)n)>((int)(' ')))
   LED += n; 
  }
  
  if (LED == "test") 
  {
    for(int x = 0; x<10; x++) {
    digitalWrite(LED_PIN, HIGH);
    delay(500);
    digitalWrite(LED_PIN, LOW);
    delay(500);
    }
  
    
  }
}

When I tested this, nothing happened. Can anyone tell me why? Any recommendations? something wrong with my code? (Note: I am not good with coding )**

If possible, I’d start by making sure voltages on the line are changing when you transmit “test” - hard to verify without a scope or logic analyzer or bus sniffer though. But, if you can do this, it will separate the problem (you’ll know if there’s an issue downstream on the arduino, or upstream on the RIO).

One thing I noticed in the arduino code: receiveEvent() assumes that all four bytes will arrive between calls to the function. I’m not 100% sure if this is guaranteed.

Say the handler called recieveEvent() right after recieving the first two characters, “te”. Your while loop will run twice, then check that “te” != “test”, and do nothing.

Whether this is your actual problem is 100% dependant on the timing of the code however, and that all the wiring is correct, and that the clock speeds configured are compatible, etc… I also don’t recall if the RIO’s transaction() function will guarantee to send out all four bytes in rapid succession, or if the arduino’s receiveEvent() callback will be guaranteed to get all 4 at the same time.

Try printing every character you recieve on the arduino side - make sure you’re seeing all four (t, e, s, t) characters before attempting to parse them in software. I’m not 100% sure from your implementation, but the string may end with a null \0 character too.