I'm trying to send a JSON String via I2C from an Arduino Uno to a RaspPi running Win IOT Core.
The connection works fine, I've registered an event handler on the Arduino side which is called fine when the master (rpi) requests data.
void I2CRequest()
{
Serial.println("I2C Request received");
/*Send data to WinIoT */
int bt = Wire.write(lastJSON.c_str());
Serial.println(lastJSON);
Serial.print("Send bytes: ");
Serial.println(bt);
}
The output on the Serial Monitor looks also fine...
I2C Request received
{"Sensor":"OneWire","data":["28ffc8675216451",23.9375,"28ff9feb521645e",24.0625]}
Send bytes: 81
The C# method on the RPi looks like this:
public static async Task<byte[]> GetI2CTemperatures()
{
var ReceivedData = new byte[1024];
/* Arduino Nano's I2C SLAVE address */
int SlaveAddress = 64; // 0x40
try
{
// Initialize I2C
var Settings = new I2cConnectionSettings(SlaveAddress);
Settings.BusSpeed = I2cBusSpeed.StandardMode;
if (AQS == null || DIS == null)
{
AQS = I2cDevice.GetDeviceSelector("I2C1");
DIS = await DeviceInformation.FindAllAsync(AQS);
}
using (I2cDevice Device = await I2cDevice.FromIdAsync(DIS[0].Id, Settings))
{
if (Device==null)
{
Debug.Write("No access to I2C Device");
}
/* Read from Arduino */
Device.Read(ReceivedData);
}
}
catch (Exception ex)
{
Debug.WriteLine("Exception occurred on reading I2C",ex);
// SUPPRESS ANY ERROR
}
/* Return received data or ZERO on error */
return ReceivedData;
}
}
Unfortunately whatever I do, I just get as a result in ReceivedData a 00 as the first byte followed by FFs.
I've tried also Device.ReadPartial() instead of Device.Read() with the same result.
Can anybody point me into the right direction what I'm doing wrong?
The write() command on the Arduino platform only writes a single byte. You are attempting to write the entire string in a single command. You will need to loop through the array and send each byte separately.
However, as soon as you do this, you will run into the 32-byte buffer limitation. It is possible to increase the buffer to 64 bytes, but this is the limit on the Uno (Atmel 328).
I put some code together to show how to setup a relationship between the Uno and the Raspberry Pi that can transfer a JSON string of varying sizes. The code is in GitHub at https://github.com/porrey/i2c.
If you want to see more ways to use I2C to communicate between an Arduino and a Raspberry Pi running Windows IoT Core see my Hackster projects at https://www.hackster.io/porrey: