UNO I2C clock stops unexpectedly.

from the lib

x = uint8_t TwoWire::endTransmission(void)

  • Output 0 .. success
  • 1 .. length to long for buffer
  • 2 .. address send, NACK received
  • 3 .. data send, NACK received
  • 4 .. other twi error (lost bus arbitration, bus error, ..)