Environment Manager

Overview

1. Read EEPROM Calibration data
2. Write to Control Register to choose temperature or pressure
3. Task loop
   1. Read data register for the measurement
   2. Convert the raw bits to Celsius or Pascals using bit manipulation
   3. Take mutex, then write the measurement to the global data variable
   4. Update task health flag to feed the watchdog

I2C

Address + W/R: 1110111 + 0/1 Write: 0xEE Read: 0xEF

Master mode: controller initiates communication

Registers

Datasheet: https://cdn-shop.adafruit.com/datasheets/BST-BMP180-DS000-09.pdf

Name	Bin	Hex	Description
ctrl_meas	11110100	0xF4	Tells sensor when to wake up and what to measure
MSB	11110110	0xF6	MSB of temperature or pressure value
LSB	11110111	0xF7	LSB of temperature or pressure value
XLSB	11111000	0xF8	(Optional) XLSB of temperature or pressure value

Control Register

Measurement	Bin	Hex	Control Register
Temperature	00101110	0x2E	ctrl_meas
Pressure	11110100	0xF4	ctrl_meas

Measurements

Uncompensated temperature (UT) and uncompensated pressure (UP): raw values in bits

Hardware

• Pull-up resistors for SCL and SDA: 4.7

Calibration

EEPROM: Every time the STM32 boots up, the calibration data must be read from the EEPROM.

• Electrically erasable programmable read-only memory
• Retains data when power is lost
• Non-volatile, byt-addressed

Purpose of Calibration: imperfections in sensor

• An equation translates electrical signals read by the sensor into data
• The 11 values are the coefficients of that equation

Steps for Calibration

1. Read 11 memory addresses     - 0xAA (10101010) to 0xBF (10111111)     - Each address has a distinct 16-bit calibration coefficient     - Since I2C registers are 8 bits, split the 16-bits into MSB and LSB     - Read MSB first     - Combine the MSB and LSB

Oversampling Setting (OSS)

Write OSS << 6 into the control register OSS controls the accuracy and noise level.

Higher OSS	Lower OSS
Sensor takes more samples and averages them	Sensor takes fewer samples and averages them
Higher accuracy	Lower accuracy
Less noise	More noise
Longer measurement time	Shorter measurement time

Bits 7 and 6 of the control register are for the oversampling setting.

• If OSS = 0: 0 << 6 = 0 (bits 7 and 6 are 00)
• If OSS = 1: 1 << 6 = 64 (bits 7 and 6 are 01)
• If OSS = 2: 2 << 6 = 128 (bits 7 and 6 are 10)
• If OSS = 3: 3 << 6 = 192 (bits 7 and 6 are 11)

Only pressure (not temperature) has OSS.

• Sensor hardware designed for single temperature reading, so there isn’t an option for oversampling or averaging.
• Temperature is less sensitive to noise.