What kind of protocol does the HX711 use?

Hello, This HX711 chip uses some kind of serial protocol. Here's the reference:

https://learn.sparkfun.com/tutorials/load-cell-amplifier-hx711-breakout-hookup-guide

And here's the library:

https://github.com/sparkfun/HX711-Load-Cell-Amplifier

It uses a clock line and a data line. It's not serial (it doesn't have a clock). It has a data and a clock signal - does that mean it's I2C? But it doesn't call it SCL and SDA. If I need to reproduce that library for a different microcontroller, how do I do it?

Thanks

The HX711 data sheet describes the serial protocol well enough that you should be able to write code for any processor, [u]especially[/u] if you follow the C code example in the data sheet.

Yes, it uses a clock line to sequence the bits.

jremington: The HX711 data sheet describes the serial protocol well enough that you should be able to write code for any processor, [u]especially[/u] if you follow the C code example in the data sheet.

Yes, it uses a clock line to sequence the bits.

Yeah, they go into quite a lot of detail on the timing. But I was wondering if this falls into one of the named protocols? Just trying where it is in the list of different clocked protocols.

Hello, did you get the protocol? I also would like to know if it is I2C or SPI

MarcosSM:
Hello, did you get the protocol? I also would like to know if it is I2C or SPI

1. If it would been an I2C Protocol, the HX711 chip should contain a provision to contain 7-bit I2C address and an I2C Logic/Interface. The Fig-1 shows a digital interface which is not an I2C Interface.


Figure-1: Typical connection diagram of HX711 chip with a load cell

2. If it would been a SPI Protocol, the HX711 chip should have a SPI interface; but, HX711does not contain such interface.

3. What is this interface for the HX711 chip?
It is a customized serial interface which has no standardized rules like the I2C Standard/protocol. The manufacturer has said that the HX711 chip is a free-running chip (it does not need any command to begin data conversion); the data lines remains at LH-state as long as data conversion is going on; at the end of data conversion, the data line assume LL-state; to bring out data bit one-after-another (with MSBit first, Fig-2) one has to assert clock pulse at the clock-pin.


Figure-2: Timing diagram of HX711 chip

4. The following sketch is the translation of the timing diagram of Fig-2. This sketch reads 10 samples of data from a load cell, averages them, and show the averaged value on the Serial Monitor.

/* This program takes 10 samples from LC + HX711B at
   1-sec interval and then computes the average.
*/

unsigned long x = 0, y=0;
unsigned long dataArray[10];
int j = 0;
void setup()
{
  Serial.begin(9600);
  pinMode(A1, INPUT); //data line  //Yellow cable
  pinMode(A0, OUTPUT);  //SCK line  //Orange cable
}

void loop()
{

  for (int j = 0; j < 10; j++)
  {
    digitalWrite(A0, LOW);//SCK is made LL
    while (digitalRead(A1) != LOW) //wait until Data Line goes LOW
      ;
    {
      for (int i = 0; i < 24; i++)  //read 24-bit data from HX711
      {
        clk();      //generate CLK pulse to get MSB-it at A1-pin
        bitWrite(x, 0, digitalRead(A1));
        x = x << 1;
      }
      clk();  //25th pulse
      Serial.println(x, HEX);
      y = x;
      x = 0;
      delay(1000);
    }
    dataArray[j] = y;
  }

  Serial.println("===averaging process=========");
  unsigned long sum = 0;

  for (j = 0; j < 10; j++)
  {
    sum += dataArray[j];
  }
  Serial.print("Average Count = ");
  sum = sum / 10;
  Serial.println(sum, HEX);
 // float W = (float)0.90*(sum-901002)/946560 + 0.75;//0.005331 * sum - 1146.176;
  //W = (float)W / 1000.00; 
  Serial.println(W, 2);
}

void clk()
{
  digitalWrite(A0, HIGH);
  digitalWrite(A0, LOW);
}

The SparkFun product page claims that it's "a true I2C interface" . Which it isn't.

This HX711 library calls it "non-i2c compliant two wire protocol" . Which is accurate.

kender: The SparkFun product page claims that it's "a true I2C interface" . Which it isn't.

This HX711 library calls it "non-i2c compliant two wire protocol" . Which is accurate.

Technically, it says IF you want true I2C interface, then use their Qwiic Scale product instead. Here's the link: https://www.sparkfun.com/products/15242