GY-63_MS5611/libraries/MS5611/README.md

MS5611

Arduino library for MS5611 pressure (and temperature) sensor.

Description

The MS5611 is a high resolution pressure (and temperature) sensor a.k.a GY-63. The high resolution is made possible by oversampling many times.

The device address is 0x76 or 0x77 depending on the CSB/CSO pin.

This library only implements the I2C interface.

An experimental SPI version of the library can be found here

• https://github.com/RobTillaart/MS5611_SPI

Self heating

In some configurations especially when using SPI the sensor showed a self heating. First this was approached as a problem, so investigations were done to understand the cause and how to solve it. During this process the view changed of seeing the higher temperature as a problem to being the solution.

The sensor is primary a pressure sensor and if it is heated by a cause (don't care) it needs compensation. For that the temperature sensor is build in the device. Depending on the configuration self heating can be as low as 0.1°C to as high as 10++ °C.

WARNING One should NOT use 5V to control I2C address line, SPI select, or the protocol select line. This causes extreme heat build up > 10°C.

One should only use 3V3 lines for these "selection lines".

See also - https://github.com/RobTillaart/MS5611_SPI/issues/3

Note: the self heating offset can be compensated with setTemperatureOffset(offset) which allows you to match the temperature with the ambient temperature again. As the self heating effect is not expected to be linear over the full range of the temperature sensor the offset might work only in a smaller range. To have a reliable ambient temperature it is advised to use an dedicated temperature sensor for this (e.g. DS18B20).

Breakout GY-63

//
//  BREAKOUT  MS5611  aka  GY63 - see datasheet
//
//  SPI    I2C
//              +--------+
//  VCC    VCC  | o      |
//  GND    GND  | o      |
//         SCL  | o      |
//  SDI    SDA  | o      |
//  CSO         | o      |
//  SDO         | o L    |   L = led
//          PS  | o    O |   O = opening  PS = protocol select
//              +--------+
//
//  PS to VCC  ==>  I2C  (GY-63 board has internal pull up, so not needed)
//  PS to GND  ==>  SPI
//  CS to VCC  ==>  0x76
//  CS to GND  ==>  0x77
//

Related libraries

For pressure conversions see - https://github.com/RobTillaart/pressure

For temperature conversions see - https://github.com/RobTillaart/Temperature

Release Notes

0.3.0 breaking change

1. fixed math error so previous versions are obsolete.
2. temperature is a float expressed in degrees Celsius.
3. pressure is a float expressed in mBar.

0.3.5 NANO 33 BLE

The I2C/Wire library of the NANO 33 BLE does not see the device on the I2C bus. After hours of testing it looks like that the I2C/Wire library of the NANO 33 BLE does not handle isConnected() like other platforms do. Adding a wire->write(0x00) in isConnected() fixes the problem, however more investigation is needed to understand the root cause.

0.3.6

The write(0) in isConnected() is made conditional explicit for the NANO 33 BLE.

The timing for convert is adjusted from TYPICAL to MAX - datasheet page 3.

0.3.7

• default address for constructor, can be set as define on the command line. MS5611_DEFAULT_ADDRESS
• added getDeviceID(), to provide a sort of unique device ID (experimental) based upon uniqueness of the factory calibration values.

0.3.8

• reset() returns bool indicating succesful ROM read
• get/setCompensation() to enable/disable compensation.

Interface

Base

• MS5611(uint8_t deviceAddress = MS5611_DEFAULT_ADDRESS) constructor. Since 0.3.7 a default address 0x77 is added.
• bool begin(uint8_t sda, uint8_t scl, TwoWire *wire = &Wire) for ESP and alike, optionally set Wire interface. Initializes internals by calling reset(). Return false indicates either isConnected() error or reset() error.
• bool begin(TwoWire *wire = &Wire) for UNO and alike, optionally set Wire interface. Initializes internals by calling reset(). Return false indicates either isConnected() error or reset() error.
• bool isConnected() checks availability of device address on the I2C bus. (see note above NANO 33 BLE).
• bool reset() resets the chip and loads constants from its ROM. Returns false if ROM could not be read.
• int read(uint8_t bits) the actual reading of the sensor. Number of bits determines the oversampling factor. Returns MS5611_READ_OK upon success.
• int read() wraps the read() above, uses the preset oversampling (see below). Returns MS5611_READ_OK upon success.
• float getTemperature() returns temperature in °C. Subsequent calls will return the same value until a new read() is called.
• float getPressure() pressure is in mBar. Subsequent calls will return the same value until a new read() is called.

Oversampling

• void setOversampling(osr_t samplingRate) sets the amount of oversampling. See table below and test example how to use.
• osr_t getOversampling() returns amount of oversampling.

Some numbers from datasheet, page 3 MAX column rounded up. (see #23) (actual read time differs - see performance sketch)

definition	value	oversampling ratio	resolution (mbar)	time (us)	notes
OSR_ULTRA_HIGH	12	4096	0.012	9100
OSR_HIGH	11	2048	0.018	4600
OSR_STANDARD	10	1024	0.027	2300
OSR_LOW	9	512	0.042	1200
OSR_ULTRA_LOW	8	256	0.065	600	Default = backwards compatible

Offset

The offset functions are added (0.3.6) to calibrate the sensor against e.g. a local weather station. This calibration can only be done runtime.

• void setPressureOffset(float offset = 0) Set an offset to calibrate the pressure. Can be used to get the pressure relative to e.g. 1 Atm. Set the offset to -1013 HPa/mBar and you get a sort of relative pressure. Default the offset is set to 0.
• float getPressureOffset() returns the current pressure offset.
• void setTemperatureOffset(float offset = 0) Set an offset to calibrate the temperature. Can be used to get the temperature in degrees Kelvin, just set the offset to +273.15. Default the offset is set to 0.
• float getTemperatureOffset() returns the current temperature offset.

Misc

• int getLastResult() checks last I2C communication. Replace with more informative error handling?
• uint32_t lastRead() last time when read() was called in milliseconds since startup.

DeviceID

• uint32_t getDeviceID() returns the hashed values of the calibration PROM. As these calibration are set in the factory and differ (enough) per sensor these can serve as an unique deviceID.

Having a device-ID can be used in many ways:

• use known offsets for each sensor automatically,
• work as an identification of that specific copy of the project (customer specific tracking).
• ID in a mesh network
• etc.

Note: this is not an official ID from the device / datasheet, it is made up from calibration data.

2nd order pressure compensation

• setCompensation(bool flag = true) to enable/desirable the 2nd order compensation. The default = true. Disabling the compensation will be slightly faster but you loose precision.
• getCompensation() returns flag set above.

Operation

See examples

Future

• update documentation
  • separate release notes?
• proper error handling.
• redo lower level functions?
• handle the read + math of temperature first?