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README.md 0.1.4 MCP9808_RT 2021-11-08 20:21:36 +01:00

Arduino CI Arduino-lint Arduino-lint License: MIT GitHub release

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 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

Constructor

  • MCP9808(const uint8_t address) constructor for e.g. UNO.
  • MCP9808(const uint8_t address, const uint8_t dataPin = 255, const uint8_t clockPin = 255) constructor for ESP32 and ESP8266.
  • bool setAddress(const uint8_t address, TwoWire *wire = &Wire) if multiple I2C buses are present one can choose. Default I2C bus is Wire.

Address

There ar 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 Conv time (ms) Samples/s Notes
0 0.5°C 30 33
1 0.25°C 65 15
2 0.125°C 130 7
3 0.0625°C 250 4 default

Note: for the same resolution it is about 3x faster than a 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 = crit 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.

Operation

See examples

Future

  • update documentation
  • do unit test
  • add more examples for the ALERT