Lecture

ESP32 I2C

25 Mar 2022 • Richard Kuo

Introduction to I2C interface, Sensors: SSD1306, HTU21DF, MAX30102, MLX90614, BMP085/BMP280 etc.

I2C (Inter-Integrated Circuit bus)

I2C Primer
Start Condition followed by 7-Bit Address of 0x64 and a Write command set. Successful I2C Write Byte Transmission Successful I2C Read Transmission

NodeMCU-32S pinout

0.96” OLED

Arduino Library: Adafruit SSD1306

Examples>Adafruit SSD1306>ssd1306_128x64_i2c

Sketchbook>OLED

HTU21DF - Relative Humidity and Temperature Digital Output

!!! 3.3V only !!! Features: Datasheet

Use I2C interface
Typical humidity accuracy of ±2%
Typical temperature accuracy of ±0.3C
Operates from 0 to 100% humidity but this sensor isn’t recommended for harsh environments where it could come in contact with water (such as rain).

Arduino Library: Adafruit HTU21DF

Sketchbook>HTU21DF

MAX30102 PPG (Photoplethysmogram) sensor

Features: Datasheet

Heart-Rate Monitor and Pulse Oximeter Sensor in LED Reflective Solution
Tiny 5.6mm x 3.3mm x 1.55mm 14-Pin Optical Module
- Integrated Cover Glass for Optimal, Robust Performance
Ultra-Low Power Operation for Mobile Devices
Programmable Sample Rate and LED Current for Power Savings• Low-Power Heart-Rate Monitor (< 1mW)
- Ultra-Low Shutdown Current (0.7μA, typ)
- Fast Data Output Capability High Sample Rates
Robust Motion Artifact Resilience: High SNR
-40°C to +85°C Operating Temperature Range

Arduino Library: Sparkfun MAX3010x

Examples>Sparkfun MAX3010x Pulse and Proximity Sensor Library>Example1_Basic_Readings

put index finger on MAX30102 will read higher value on R & IR
Examples>Sparkfun MAX3010x Pulse and Proximity Sensor Library>Example4_HeartBeat_plotter

Sketch> Sensors> MAX30102_OLED_BPM

MAX30102_OLED_BPM

MLX90614 Infrared Thermometer

Datasheet

Factory calibrated in wide temperature range: -40 to 125 ˚C for sensor temperature and -70 to 380 ˚C for object temperature.
High accuracy of 0.5°C over wide temperature range (0..+50°C for both Ta and To)
High (medical) accuracy calibration
Measurement resolution of 0.02°C
SMBus compatible digital interface
Available in 3V and 5V versions
Automotive grade

MLX90614::readObjectTempC()

Arduino Library: Adafruit MLX90614

Adafruit_MLX90614.h
Adafruit_MLX90614.cpp

MLX90614.read16() will read 2 bytes + pec

uint16_t Adafruit_MLX90614::read16(uint8_t a) {
  uint8_t buffer[3];
  buffer[0] = a;
  // read two bytes of data + pec
  bool status = i2c_dev->write_then_read(buffer, 1, buffer, 3);
  if (!status)
    return 0;
  // return data, ignore pec
  return uint16_t(buffer[0]) | (uint16_t(buffer[1]) << 8);
}

MLX90614.write16() will write 1 address + 2 bytes + pec

void Adafruit_MLX90614::write16(uint8_t a, uint16_t v) {
  uint8_t buffer[4];

  buffer[0] = _addr << 1;
  buffer[1] = a;
  buffer[2] = v & 0xff;
  buffer[3] = v >> 8;

  uint8_t pec = crc8(buffer, 4);

  buffer[0] = buffer[1];
  buffer[1] = buffer[2];
  buffer[2] = buffer[3];
  buffer[3] = pec;

  i2c_dev->write(buffer, 4);
}

Examples>Adafruit MLX90614 Library>mlxtest

BH1750 Ambient Light Sensor (光照感測器)

採用ROHM原裝BH1750FVI晶片
供電電源：3-5v
資料範圍：0-65535
感測器內置16bitAD轉換器
直接數位輸出，省略複雜的計算，省略標定
不區分環境光源
接近於視覺靈敏度的分光特性
可對廣泛的亮度進行1勒克斯的高精度測

Arduino Library: BH1750

Examples> BH1750> BH1750advanced

Barometer（氣壓計）

BMP085