RobTillaart / HX710AB

Arduino library for the HX710A and HX710B 24-Bit ADC.

HX710AB

Arduino library for the HX710A and HX710B 24-Bit ADC.

Description

Experimental

This library provides two classes to read the HX710A and the HX710B ADC.

(from datasheet)

The HX710(A/B) is a precision 24-bit analog-to-digital converter (ADC) with built-in temperature sensor (HX710A) or DVDD, AVDD voltage difference detection (HX710B). It’s designed for weigh scales and industrial control applications to interface directly with a bridge sensor.

The HX710A can read the internal temperature.

THe HX710B can read the DVDD and AVDD supply voltage difference.

The HX710 has no means to detect errors, however several readings without noise especially zero's might be an indication that something is wrong.

The HX710 is closely related to the HX711 which has more features. These are not 1-to-1 replaceable devices.

Breaking changes 0.2.0

Some functions have been renamed to bring the API in line with the HX711 library.

Pre-0.2.0 (experimental) versions are therefore obsolete.

Performance

Performance depends on platform used and on the time to make a measurement. The latter is either 10 or 40 Hz, which possibly means optional 100 or 25 milliseconds extra waiting time.

To minimize the blocking time the library implemented (0.1.2) an asynchronous interface to keep performance at maximum level.

Related

• https://github.com/RobTillaart/HX710AB this library.
• https://github.com/RobTillaart/HX711 for load cells.
• https://github.com/RobTillaart/HX711_MP for load cells with multipoint calibration.
• https://swharden.com/blog/2022-11-14-hx710b-arduino/ usage with pressure sensor.
• https://http://www.aviaic.com/ (manufacturer)
• https://github.com/RobTillaart/weight conversions
• https://github.com/RobTillaart/pressure conversions

Test

Tested HX710B with Arduino UNO.

• raw readings work
• pressure sensor drifts.
• two sensors tested have very different "zero point"

Interface

#include "HX710AB.h"

Constructor

Two classes:

• HX710A(uint8_t dataPin, uint8_t clockPin) constructor.
• HX710B(uint8_t dataPin, uint8_t clockPin) constructor.
• void begin(bool fastProcessor = false) initialises pins. The fastProcessor option adds a 1 uS delay for each clock half-cycle to keep the time greater than 200 nS. If data does not makes sense, not stable one can try this flag.

Read, synchronous

• int32_t read(bool differential = true) powers up the device, reads from the device, sets the mode for the next read. The default parameter is true as differential readings are most used. See table below.
• uint32_t last_time_read() returns last time a value was read in milliseconds.
• int32_t last_value_read() returns last read value, note this can be differential or other. The user should keep track of this.

differential	HX710A	HX710B	notes
true	differential	differential	default
false	temperature	DVDD and AVDD

Read, asynchronous

As the device might be blocking for up to 100 millis when using the synchronous read(), the library offers an async way to read the device. This allows the user to do other tasks instead of active waiting. In fact the read() is implemented with this async interface.

• void request() wakes up the device to make a measurement.
• bool is_ready() checks if a measurement is ready.
• int32_t fetch(bool differential = true) reads from the device, sets the mode for the next read. The default parameter is true as differential readings are most used. See table above.

Calibration

The calibration for the HX710 is a two point calibration. The reason for a two point calibration is that in contrast to the HX711 for load cells, there is no "natural zero" per se.

One need to do two measurements M1(raw1, out1) and M2(raw2, out2). These exists of two raw read() values for two known / calibrated unit values.

With these two measurements the linear relation is derived

units = (raw_in - offset) * scale;

After calibration one can get the parameters from the formula, to be stored e.g. in EEPROM for a next time e.g. after reboot.

• bool calibrate(int32_t raw1, float out1, int32_t raw2, float out2) calculates the scale and offset from the two measurements. returns false if (raw1 == raw2) or (out1 == out2) as then scale and/or offset can not be calculated.
• int32_t get_offset() returns offset from the formula to store for next time.
• float get_scale() returns scale from the formula to store for next time.
• void set_offset(uint32_t offset) set offset in the formula (e.g. from EEPROM)
• bool set_scale(float scale) set scale in the formula (e.g. from EEPROM) Returns false if scale is set to zero as this would make all measurements zero.

In code this could look like

//  save calibration data
HXB.calibrateUnit(125465, 1019.2,  159864, 1025.6);
EEPROM.set(offset_address, HXB.getOffset());
EEPROM.set(scale_address, HXB.getScale());


//  load calibration data
HXB.setOffset(EEPROM.get(offset_address));
HXB.setScale(EEPROM.get(scale_address));

The values from offset and scale should be compatible with the HX711 library. However this is not tested (yet).

Units

• float get_units() read the device in calibrated units. Works only after calibration, see above.

Power

• void power_down() puts the device in sleep mode (after 60 us).
• void power_up() wakes up device.

Note the read() and fetch() functions automatically wake up the device. So powerUp() is seldom needed.

Future

Must

• improve documentation

Should

• test extensively

Could

• extend unit tests(?)
• more examples.
• extend performance test sketch
• AVR optimized code - see FastShiftIn. (low gain as sensor blocks at 10/40 Hz)

Wont

• bool isPowerUp();

Support

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Thank you,