GY-63_MS5611/libraries/MCP9808_RT/README.md

MCP9808_RT

Arduino library for I2C MCP9808 temperature sensor.

Description

The MCP9808 is a temperature sensor that measures typically in 1/16th == 0.0625° Celsius. What makes this sensor interesting is the ALERT pin, which allows triggering of any piece of electronics if the temperature hits a predefined value or temperature zone.

MCP9808 breakout board

//
//       Adafruit MCP9808 breakout board
//       +----------+
//       |0   ALERT |---------------+--[ 4K7 ]---- +5V
//       |       A2 |---- GND       |
//       |       A1 |---- GND       +--[ LED ]---- GND  // or other electronics.
//       |       A0 |---- GND
//       |      SDA |---- I2C MCU
//       |      SCL |---- I2C MCU
//       |      GND |---- GND MCU
//       |0     VCC |---- +5V
//       +----------+
//
//       address above is 24
//

Interface

#include "mcp9808.h"

Constructor

• MCP9808(const uint8_t address, TwoWire *wire = &Wire) Set the device address. Option one can set the I2C bus if multiple I2C buses are present. Default I2C bus is Wire.

0.4.0 Breaking change

The user must initialize the I2C bus in setup(), the library doesn't do that since 0.4.0. So one need to call Wire.begin() or Wire.begin(SDA, SCL).

Address

There are max 8 sensors on one I2C bus. Normal address = 0011xxx where xxx = A2, A1, A0

Address	HEX	A2	A1	A0
24	0x18	0	0	0
25	0x19	0	0	1
26	0x1A	0	1	0
27	0x1B	0	1	1
28	0x1C	1	0	0
29	0x1D	1	0	1
30	0x1E	1	1	0
31	0x1F	1	1	1

On request manufacturer will provide 1001xxx as base address allowing up to 16 temp sensors on one bus.

Temperature and status

• void setOffset(float offset = 0.0) set an offset to calibrate or to correct for self heating. The value of offset is not validated to keep footprint small.
• float getOffset() return value of offset (default 0).
• float getTemperature() read the ambient temperature.
• uint8_t getStatus() returns the status bits of the last call to getTemperature()

The value returned by getStatus() is the last value read by the call to GetTemperature().
There are three bits, see table below. A value of 6 == mask == 110 means that TA is above the upper AND above the critical temperature.

Bit	Mask	Description	Notes
0	0x01	TA < TLOWER	lower
1	0x02	TA > TUPPER	larger
2	0x04	TA ≥ TCRIT	larger or equal

Resolution

• void setResolution(uint8_t resolution = 3) set the resolution, if resolution > 3, it is not set.
• uint8_t getResolution() returns the resolution set.

Value	Resolution	Conversion	Samples/s	Notes
0	0.5°C	30 ms	33
1	0.25°C	65 ms	15
2	0.125°C	130 ms	7
3	0.0625°C	250 ms	4	default

Note: for the same resolution the MCP9808 is about 3x faster than the popular DS18B20.

Configuration

• void setConfigRegister(uint16_t configuration) see table below + read datasheet.
• uint16_t getConfigRegister() return set value.

Bit	Mask	Name	Description	Value
0	0x0001	ALT MOD	alert mode	0 = comparator output, 1 = interrupt output
1	0x0002	ALT POL	alert polarity	0 = active low, 1 = active high
2	0x0004	ALT SEL	alert select	0 = upper+lower+crit, 1 = critical only
3	0x0008	ALT CNT	alert control	0 = OFF, 1 = ON
4	0x0010	ALT STAT	alert status	0 = OFF, 1 = ON (read!)
5	0x0020	INT CLR	interrupt clear	0 = none, 1 = clear interrupt
6	0x0040	WIN LOC	lock Tup + Tlow	0 = unlocked, 1 = Lock
7	0x0080	CRT LOC	lock Tcritical	0 = unlocked, 1 = Lock
8	0x0100	SHDN	shutdown,	0 = continuous mode, 1 = low power
9-10	0x0600	Hysteresis	Thysteresis	00 = 0°C, 01 = 1.5°C, 10 = 3°C, 11 = 6°C
11-15		always 0

Check datasheet for the details...

Temperature limits / thresholds

• void setTupper(float temp) write upper register, accuracy 0.25°C.
• float getTupper() idem.
• void setTlower(float temp) write lower register, accuracy 0.25°C.
• float getTlower() idem.
• void setTcritical(float temp) write critical register, accuracy 0.25°C.
• float getTcritical() idem.

The values written in these registers, are the trigger values for the status read with getStatus. Note that the Hysteresis temperature delta affects the value of these triggers.

The values set are not validated to keep footprint of the library small.

Miscellaneous

• uint16_t getManufacturerID() returns 84 (my version).
• uint8_t getDeviceID() returns 0 (my version).
• uint8_t getRevision() returns 84 (my version).
• uint16_t getRFU() returns 29 (my version). Reserved for future use.

Hidden registers

The MCP9808 has hidden registers mentioned only on p.16 of the datasheet. These are for testing and calibration. The library prevents reading / writing them to keep sensors working.

Future

Must

• refactor the constructor to include Wire param
• add begin() function.

Should

• update documentation
  • compare DS18B20?
• test more
  • negative temperatures
• do unit test
• check for optimizations

Could

• add examples
  • for the ALERT
  • multi sensor

Wont

Support

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Thank you,