The personal website of Scott W Harden
November 15th, 2022

Interfacing HX710 Differential ADC with Arduino

This page demonstrates how to read differential voltage from a HX710 ADC using Arduino. I recently obtained some pressure sensor boards from Amazon for less than $3 each under names like 6pcs 3.3-5V Digital Barometric Air Pressure Sensor Module Liquid Water Level Controller Board 0-40KPa that use this ADC. Several years ago I worked on a precision pressure meter project based on an I2C temperature and pressure sensor (MS5611), and now that I see new inexpensive SPI pressure sensor modules on the consumer market I'm interested to learn more about their capabilities.

Analog-to-Digital Converter IC

The ADC chip is easily identified as a HX710B 24-Bit Analog-to-Digital Converter (ADC) with Built-in Temperature Sensor. According to the datasheet it can be powered by a 3.3V or 5V supply, and the value it reports is the differential voltage between two input pins.

The datasheet indicates this device can be run from a 3.3V or 5V supply, it uses a built-in fixed-gain (128x) differential amplifier, and it can read up to 40 samples per second. The datasheet provides an example circuit demonstrating how this ADC can be used to measure weight from a scale sensor:

Pressure Sensor

To get a better idea of how this sensor works it would be helpful to locate its product number. I had a hunch it was beneath the part so I desoldered it, and indeed I found part identification information.

The pressure sensor is labeled as a PSG010S but unfortunately I struggled to find a quality datasheet for it. I did find some now-deleted images from an AliExpress listing showing the differences between the base model and the R and S variants. I found this PSG010R datasheet (curiously written in Comic Sans) indicating that maximum voltage is 5V and that the gauge pressure is 0 - 40KPa (0 - 5.8 PSI). This seems to be a fairly standard differential pressure sensor design using a pair of voltage dividers where the pressure is a function of the difference in voltage at the two mid-points (a Wheatstone bridge).

Read HX710B with Arduino

This code demonstrates how to measure HX710B values using Arduino and display the readings in the serial terminal sufficient to graph in real time using the serial plotter. The animated plot is what it looks like when I blow puffs of air on the sensor.

const int HX_OUT_PIN = 2;
const int HX_SCK_PIN = 3;

enum HX_MODE { NONE, DIFF_10Hz, TEMP_40Hz, DIFF_40Hz};
const byte HX_MODE = DIFF_40Hz;

void setup() {
  pinMode(HX_SCK_PIN, OUTPUT);
  pinMode(HX_OUT_PIN, INPUT);
  Serial.begin(9600);
}

void loop() {
  Serial.println(readHX());
}

unsigned long readHX() {

  // pulse clock line to start a reading
  for (char i = 0; i < HX_MODE; i++) {
    digitalWrite(HX_SCK_PIN, HIGH);
    digitalWrite(HX_SCK_PIN, LOW);
  }

  // wait for the reading to finish
  while (digitalRead(HX_OUT_PIN)) {}

  // read the 24-bit pressure as 3 bytes using SPI
  byte data[3];
  for (byte j = 3; j--;) {
    data[j] = shiftIn(HX_OUT_PIN, HX_SCK_PIN, MSBFIRST);
  }

  data[2] ^= 0x80;  // flip the 'out of range' error bit

  // shift the 3 bytes into a large integer
  long result;
  result += (long)data[2] << 16;
  result += (long)data[1] << 8;
  result += (long)data[0];

  return result;
}

Open-Source HX710B Libraries

Although some libraries are available which facilitate interacting with the HX710, here I engage with it discretely to convey each step of the conversion and measurement process. I found that many libraries use the 10 Hz mode by default, whereas I certainly prefer the 40 Hz mode. More frustratingly, code in many libraries refer to this as gain, which is incorrect. The datasheet indicates gain is fixed at 128 and cannot be changed in software.

Resources

Markdown source code last modified on November 17th, 2022
---
Title: Interfacing HX710 Differential ADC with Arduino
Description: How to read differential voltage from a HX710 ADC using Arduino
Date: 2022-11-15 12:30AM EST
Tags: circuit, microcontroller
---

# Interfacing HX710 Differential ADC with Arduino

**This page demonstrates how to read differential voltage from a HX710 ADC using Arduino.** I recently obtained some pressure sensor boards from Amazon for less than $3 each under names like _6pcs 3.3-5V Digital Barometric Air Pressure Sensor Module Liquid Water Level Controller Board 0-40KPa_ that use this ADC. Several years ago I worked on a [precision pressure meter project](https://swharden.com/blog/2017-04-29-precision-pressure-meter-project/) based on an [I2C](https://en.wikipedia.org/wiki/I%C2%B2C)  temperature and pressure sensor ([MS5611](https://www.te.com/commerce/DocumentDelivery/DDEController?Action=showdoc&DocId=Data+Sheet%7FMS5611-01BA03%7FB3%7Fpdf%7FEnglish%7FENG_DS_MS5611-01BA03_B3.pdf%7FCAT-BLPS0036)), and now that I see new inexpensive [SPI](https://en.wikipedia.org/wiki/Serial_Peripheral_Interface) pressure sensor modules on the consumer market I'm interested to learn more about their capabilities.

<img src="hx710b-pressure-board.jpg" class="my-5 border border-dark shadow img-fluid w-75 mx-auto d-block">

## Analog-to-Digital Converter IC

**The ADC chip is easily identified as a [HX710B](https://www.electronicscomp.com/datasheet/hx710b-ic-datasheet.pdf) _24-Bit Analog-to-Digital Converter (ADC) with Built-in Temperature Sensor_.** According to the datasheet it can be powered by a 3.3V or 5V supply, and the value it reports is the differential voltage between two input pins. 

<img src="hx710b-pinout.jpg" class="my-5 img-fluid w-75 mx-auto d-block">

The datasheet indicates this device can be run from a 3.3V or 5V supply, it uses a built-in fixed-gain (128x) differential amplifier, and it can read up to 40 samples per second. The datasheet provides an example circuit demonstrating how this ADC can be used to measure weight from a scale sensor:

<img src="hx710-datasheet.jpg" class="my-5 img-fluid w-75 mx-auto d-block">

## Pressure Sensor

To get a better idea of how this sensor works it would be helpful to locate its product number. I had a hunch it was beneath the part so I desoldered it, and indeed I found part identification information.

<img src="hx710b-pressure-psg010s.jpg" class="my-5 border border-dark shadow img-fluid w-75 mx-auto d-block">

**The pressure sensor is labeled as a PSG010S** but unfortunately I struggled to find a quality datasheet for it. I did find some now-deleted images from an AliExpress listing showing the differences between the base model and the R and S variants. 
I found [this PSG010R datasheet](https://www.katranji.com/tocimages/files/536845-544144.pdf) (curiously written in Comic Sans) indicating that maximum voltage is 5V and that the gauge pressure is 0 - 40KPa (0 - 5.8 PSI). This seems to be a fairly standard [differential pressure sensor](https://www.avnet.com/wps/portal/abacus/solutions/technologies/sensors/pressure-sensors/measurement-types/differential/) design using a pair of voltage dividers where the pressure is a function of the difference in voltage at the two mid-points (a [Wheatstone bridge](https://en.wikipedia.org/wiki/Wheatstone_bridge)).


<img src="psg-pressure-sensor.jpg" class="my-5 border border-dark shadow img-fluid w-75 mx-auto d-block">

## Read HX710B with Arduino

**This code demonstrates how to measure HX710B values using Arduino** and display the readings in the serial terminal sufficient to graph in real time using the serial plotter. The animated plot is what it looks like when I blow puffs of air on the sensor.

<img src="hx710-arduino-plot.gif" class="my-5 img-fluid mx-auto d-block">

```c
const int HX_OUT_PIN = 2;
const int HX_SCK_PIN = 3;

enum HX_MODE { NONE, DIFF_10Hz, TEMP_40Hz, DIFF_40Hz};
const byte HX_MODE = DIFF_40Hz;

void setup() {
  pinMode(HX_SCK_PIN, OUTPUT);
  pinMode(HX_OUT_PIN, INPUT);
  Serial.begin(9600);
}

void loop() {
  Serial.println(readHX());
}

unsigned long readHX() {

  // pulse clock line to start a reading
  for (char i = 0; i < HX_MODE; i++) {
    digitalWrite(HX_SCK_PIN, HIGH);
    digitalWrite(HX_SCK_PIN, LOW);
  }

  // wait for the reading to finish
  while (digitalRead(HX_OUT_PIN)) {}

  // read the 24-bit pressure as 3 bytes using SPI
  byte data[3];
  for (byte j = 3; j--;) {
    data[j] = shiftIn(HX_OUT_PIN, HX_SCK_PIN, MSBFIRST);
  }
  
  data[2] ^= 0x80;  // flip the 'out of range' error bit

  // shift the 3 bytes into a large integer
  long result;
  result += (long)data[2] << 16;
  result += (long)data[1] << 8;
  result += (long)data[0];

  return result;
}
```

## Open-Source HX710B Libraries

Although some libraries are available which facilitate interacting with the HX710, here I engage with it discretely to convey each step of the conversion and measurement process. I found that many libraries use the 10 Hz mode by default, whereas I certainly prefer the 40 Hz mode. More frustratingly, code in many libraries refer to this as _gain_, which is incorrect. The datasheet indicates gain is fixed at 128 and cannot be changed in software.

## Resources

* [Pressure Sensor Guide](https://www.electroschematics.com/pressure-sensor-guide/) by T.K. HAREENDRAN - A similar write-up that goes into additional detail. They didn't de-solder the pressure sensor to identify the component name, but there's lots of good information on this page.

* [bogde/HX711 on GitHub](https://github.com/bogde/HX711) - An Arduino library to interface the Avia Semiconductor HX711 24-Bit Analog-to-Digital Converter (ADC) for reading load cells / weight scales. Code on this page does not use this library, but others may find it helpful.

* [HX710 datasheet (English)](https://www.electronicscomp.com/datasheet/hx710b-ic-datasheet.pdf)

* [Differential pressure sensors](https://www.avnet.com/wps/portal/abacus/solutions/technologies/sensors/pressure-sensors/measurement-types/differential/) - Article about the topic which includes a good example of an instrumentation amplifier.

* [Design tips for a resistive-bridge pressure sensor in industrial process-control systems](https://www.ti.com/lit/an/slyt640/slyt640.pdf) - Texas Instruments application note

* [The Wheatstone Bridge](https://meritsensor.com/the-wheatstone-bridge/) by Michael Daily