I2C communication between load cell and Arduino

Question

I am using Load Cell (FX29 Data Sheet) and Arduino for measuring force. Every time I disconnect and reconnect Arduino from USB I get one of the following readings on serial monitor:

1. Correct expected values
2. Zero value (sensor returns "0" value and does not increment)
3. Maximum possible reading i.e. 16383 for 14 bits

I'm not able to understand the reason. What could be the possible directions for debugging the issue?

Circuit Diagram:

Answer 1

From the code that you are based on:

  Wire.requestFrom(curAddress, 2); //Requests two bytes of data 
  byte msb = Wire.read();
  byte lsb = Wire.read();

This code send a request for reading two bytes from the I2C slave, it then immediately read the input buffer without checking whether the data is actually available or not, as the result you will get whatever in the i2c buffer instead of the actual reading. The following code is a more reliable implementation:

  Wire.requestFrom(curAddress, 2, true);  // true - send STOP at end of data transfer
  while (Wire.available() != 2) {};       // wait until two bytes are received
  int16_t dataVal = (int16_t) ( (Wire.read() & 0x3f) << 8 ) | Wire.read();