ADC LTC2433-1 on Leonardo

Other Hardware Sensors
21

If you want to have 16bits of integer information and the sign information you need to change to the 32bit variant:

void loop() {
  delay(2000);
  digitalWrite(CSPin, LOW);
  delay(1);

  byte1 = SPI.transfer(0);
  byte2 = SPI.transfer(0);
  byte3 = SPI.transfer(0);
  delay(1);
  digitalWrite(CSPin, HIGH);

  int32_t v = byte1;
  v <<= 11;
  v |= ((int) byte2) << 3;
  v |= byte3 >> 5;
  if (byte1 & 0x20) {
    v = -v;
  }
}
22

There's something I do not understand.
My ADC is 16 bit it should give 65535 in decimal.

If I use your old code I get an output from unloaded stain gauge: 1340

uint16_t v = byte1;
v <<= 11;
v |= ((uint16_t) byte2) << 3;
v |= byte3 >> 5;

Serial.println(v);

If I use your new code I get an output from unloaded stain gauge: 66862

int32_t v = byte1;
  v <<= 11;
  v |= ((int) byte2) << 3;
  v |= byte3 >> 5;
  
Serial.println(v);
23

We need to mask out the flag bits in the first byte:

int32_t v = byte1 & 0x1F;
  v <<= 11;
  v |= ((int) byte2) << 3;
  v |= byte3 >> 5;
  
Serial.println(v);