Dual channel HX711 load cell interface

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Selected firmware excerpt. The diagram explains the code; it is not a hardware test.

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// Helpers to select channel and discard the first sample (gain applies to next conversion)
void selectChannelA() {
  hx.set_gain(128);   // set next conversion to A, gain 128
  hx.read();          // dummy read to apply
}
void selectChannelB() {
  hx.set_gain(32);    // set next conversion to B, gain 32
  hx.read();          // dummy read to apply
}

// Read raw average on current channel
long readRawAverage(uint16_t samples) {
  long sum = 0;
  for (uint16_t i = 0; i < samples; i++) {
    while (!hx.is_ready()) { /* wait */ }
    sum += hx.read();
  }
  return (long)( (double)sum / samples );
}

// Per-channel tare
void tareChannelA() {
  selectChannelA();
  offsetA = readRawAverage(SAMPLES_PER_READ * 3);
}
void tareChannelB() {
  selectChannelB();
  offsetB = readRawAverage(SAMPLES_PER_READ * 3);
}