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278 lines
9.9 KiB
Markdown
278 lines
9.9 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/MS5611_SPI/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/MS5611_SPI/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/MS5611_SPI/blob/master/LICENSE)
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[](https://github.com/RobTillaart/MS5611_SPI/releases)
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# MS5611_SPI
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Arduino library (SPI) for MS5611 pressure (and temperature) sensor.
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## Description
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The MS5611 is a high resolution pressure (and temperature) sensor a.k.a GY-63.
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The high resolution is made possible by oversampling many times.
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This library only implements the SPI interface.
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Based upon the 0.3.6 version of the I2C library,
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see - https://github.com/RobTillaart/MS5611
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#### Compatibility
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The library should be compatible with MS56XX, MS57xx and MS58xx devices (to be tested).
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Some device types will returns only 50% of the pressure value.
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This is solved by calling **reset(1)** to select the math used.
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#### Self heating
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In some configurations especially when using SPI the sensor showed a self heating.
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First this was approached as a problem, so investigations were done to understand the
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cause and how to solve it. During this process the view changed of seeing the higher
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temperature as a problem to being the solution.
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The sensor is primary a pressure sensor and if it is heated by a cause (don't care)
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it needs compensation. For that the temperature sensor is build in the device.
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Depending on the configuration self heating can be as low as 0.1°C to as high as 10++ °C.
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**WARNING** One should **NOT** use 5V to control I2C address line, SPI select, or
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the protocol select line. This causes extreme heat build up > 10°C.
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One should only use 3V3 lines for these "selection lines".
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See also - https://github.com/RobTillaart/MS5611_SPI/issues/3
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Note: the self heating offset can be compensated with **setTemperatureOffset(offset)**
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which allows you to match the temperature with the ambient temperature again.
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As the self heating effect is not expected to be linear over the full range of the
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temperature sensor the offset might work only in a smaller range.
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To have a reliable ambient temperature it is advised to use an dedicated temperature sensor for this (e.g. DS18B20).
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#### Breakout GY-63
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```cpp
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//
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// BREAKOUT MS5611 aka GY63 - see datasheet
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//
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// SPI I2C
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// +--------+
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// VCC VCC | o |
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// GND GND | o |
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// SCL | o |
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// SDI SDA | o |
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// CSO | o |
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// SDO | o L | L = led
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// PS | o O | O = opening PS = protocol select
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// +--------+
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//
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// PS to VCC ==> I2C (GY-63 board has internal pull up, so not needed)
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// PS to GND ==> SPI
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// CS to VCC ==> 0x76
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// CS to GND ==> 0x77
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//
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```
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#### Related libraries
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For pressure conversions see - https://github.com/RobTillaart/pressure
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For temperature conversions see - https://github.com/RobTillaart/Temperature
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## WARNING EXPERIMENTAL
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Note: This library is under development
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SPI communication works and reasonable values are read, at least for pressure.
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All SPI tests so far gave too high temperatures, some were rising slowly, others faster.
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Values are read correctly but somehow the selection of SPI as protocol seems to cause internal heating.
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This self heating has been confirmed and is discussed - https://github.com/RobTillaart/MS5611_SPI/issues/3
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Some results of experiments:
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| Platform | tested | time (us)| Notes |
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|:----------------|-------:|:--------:|--------:|
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| UNO SW SPI | fail | | temperature is rising very fast (stopped) ==> DO NOT USE 5V
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| UNO HW SPI | fail | | no data,
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| ESP32 SW SPI V | Y | 1299 | VSPI pins; temperature is rising slowly
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| ESP32 SW SPI H | Y | 1298 | HSPI pins; temperature too high (+3) but stable
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| ESP32 HSPI | Y | 1396 | temperature is rising slowly and stabilizes
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| ESP32 VSPI | Y | 1395 | temperature is rising slowly and stabilizes
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| NANO 33 SW SPI | - | - | not tested yet
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| NANO 33 HW SPI | - | - | not tested yet
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#### Note UNO
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For VCC 3V3 was used as the other pins CLK and SDI have a voltage converter in the GY-63.
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- Unclear why HW SPI blocks for UNO.
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- The 5V voltage is definitely too high for the sensor, but protocol wise it was expected to work.
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- it might be a timing issue as the ESP32 showed some improvement when "fiddle the timing"
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#### Note ESP32
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H-SPI pins:
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- not reliable at start, incorrect PROM reads, both HW and SW.
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- adjusting the timing improves this a bit.
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- these pins also interfere with uploading sketches.
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#### Conclusion for now
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There are a few open ends to investigate.
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- investigate an UNO with a level converter (for selection pins)
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- investigate timing (clock) of the SPI. (both ESP and UNO)
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If you have experiences with this library please share them in the issues.
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## Release Notes
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### 0.1.0 initial release
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Based upon 0.3.8 of the I2C MS5611 library.
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## Interface
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#### Base
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- **MS5611_SPI(uint8_t select, uint8_t dataOut = 255, uint8_t dataIn = 255, uint8_t clock = 255)** constructor.
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- **bool begin()** initializes internals,
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- **bool isConnected()** checks device by calling **read()**.
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- **bool reset(uint8_t mathMode = 0)** resets the chip and loads constants from its ROM.
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Returns false if ROM could not be read.
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- mathMode = 0 follows the datasheet math (default).
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- mathMode = 1 will adjust for a factor 2 in the pressure math.
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- **int read(uint8_t bits)** the actual reading of the sensor.
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Number of bits determines the oversampling factor. Returns MS5611_READ_OK upon success.
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- **int read()** wraps the **read()** above, uses the preset oversampling (see below).
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Returns MS5611_READ_OK upon success.
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- **float getTemperature()** returns temperature in °C.
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Subsequent calls will return the same value until a new **read()** is called.
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- **float getPressure()** pressure is in mBar.
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Subsequent calls will return the same value until a new **read()** is called.
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#### Oversampling
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- **void setOversampling(osr_t samplingRate)** sets the amount of oversampling.
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See table below and test example how to use.
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- **osr_t getOversampling()** returns amount of oversampling.
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Some numbers from datasheet, page 3 MAX column rounded up. (see #23)
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(actual read time differs - see performance sketch)
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| definition | value | oversampling ratio | resolution (mbar) | time (us) | notes |
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|:--------------:|:-----:|:------------------:|:-----------------:|:---------:|:------:|
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| OSR_ULTRA_HIGH | 12 | 4096 | 0.012 | 9100 |
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| OSR_HIGH | 11 | 2048 | 0.018 | 4600 |
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| OSR_STANDARD | 10 | 1024 | 0.027 | 2300 |
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| OSR_LOW | 9 | 512 | 0.042 | 1200 |
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| OSR_ULTRA_LOW | 8 | 256 | 0.065 | 600 | Default = backwards compatible
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#### Offset
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The offset functions are added (0.3.6) to calibrate the sensor against e.g. a local weather station.
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This calibration can only be done runtime.
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- **void setPressureOffset(float offset = 0)** Set an offset to calibrate the pressure.
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Can be used to get the pressure relative to e.g. 1 Atm.
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Set the offset to -1013 HPa/mBar and you get a sort of relative pressure.
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Default the offset is set to 0.
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- **float getPressureOffset()** returns the current pressure offset.
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- **void setTemperatureOffset(float offset = 0)** Set an offset to calibrate the temperature.
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Can be used to get the temperature in degrees Kelvin, just set the offset to +273.15.
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Default the offset is set to 0.
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- **float getTemperatureOffset()** returns the current temperature offset.
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#### Misc
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- **int getLastResult()** checks last I2C communication. Replace with more informative error handling?
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- **uint32_t lastRead()** last time when **read()** was called in milliseconds since startup.
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#### DeviceID
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- **uint32_t getDeviceID()** returns the hashed values of the calibration PROM.
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As these calibration are set in the factory and differ (enough) per sensor these can serve as an unique deviceID.
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Having a device-ID can be used in many ways:
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- use known offsets for each sensor automatically,
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- work as an identification of that specific copy of the project (customer specific tracking).
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- ID in a mesh network
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- etc.
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Note: this is not an official ID from the device / datasheet, it is made up from calibration data.
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#### getManufacturer
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The meaning of the manufacturer and serialCode value is unclear.
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- **uint16_t getManufacturer()** returns manufacturer private info.
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- **uint16_t getSerialCode()** returns serialCode from the PROM\[6].
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#### 2nd order pressure compensation
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- **setCompensation(bool flag = true)** to enable/desiable the 2nd order compensation.
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The default = true.
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Disabling the compensation will be slightly faster but you loose precision.
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- **getCompensation()** returns flag set above.
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#### SPI functions
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// to be tested.
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- **void setSPIspeed(uint32_t speed)**
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- **uint32_t getSPIspeed()**
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- **bool usesHWSPI()**
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#### SPI - ESP32 specific
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// to be tested.
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- **void selectHSPI()**
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- **void selectVSPI()**
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- **bool usesHSPI()**
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- **bool usesVSPI()**
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- **void setGPIOpins(uint8_t clk, uint8_t miso, uint8_t mosi, uint8_t select)**
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## Operation
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See examples
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## Future
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#### must
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- update documentation
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- follow I2C library.
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- investigate internal heating with SPI.
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#### should
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- proper error handling.
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- move all code to .cpp
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#### could
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- redo lower level functions?
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- handle the read + math of temperature first?
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