IoT End Devices
Karel Slavicek
Vaclav Oujezsky
2024
Schedule update
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Next week, 8th of October, the lecture at 10:00 is
canceled.
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Lab exercises take place according to schedule.
Global remarks
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Overview of available components
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Don’t try to memorize it all
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Key reprezetatives available in the lab
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More components on demand
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Very very brief excursion into electronic design
Structure of an IoT System
Structure of an IoT System
Overview
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HMI
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Input devices
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Displays
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Environmental sensors
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Proximity, positioning and inertial measurements
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Biometric
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Data storage and supportive devices
HMI Input Devices
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Pushbuttons and switches
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Capacitive / Inductive touch sensors
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Keyboard
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Rotary encoder
Pushbuttons and switches
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Frequently with „negative“ logic:
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Possible utilization of internal pull-up resistors of MCU
Keyboard
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Rows and columns
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Set all row pins as Input_Pullup
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Go column by column
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Set column pin output LOW
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Read all row pins
Rotary encoder
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Counting pulses
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Clockwise
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Counterclockwise
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Navigation in a list
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Zooming in / out
Displays
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LED, RGB LED, LED matrix
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7-Segment LED
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LCD
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TFT
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OLED
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E-Paper
LED, RBG LED
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Current limited by resistor
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Light intensity regulated by PWM (Pulse-Width
Modulation)
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Resistor value computation:
Ohms law
U = R x I
LED, RGB LED – Ohms law
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Commonly, the LED can
survive up to 20 mA
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1 – 2 mA should be enough
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R = (U – 2V) / 2mA
R = (3.3V – 2V) / 2mA = 650 Ω
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Nearest common value 680 Ω
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Required precision of current set: low
RGB LED
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Three LED diodes in one package
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Both common cathode and common anode
LED, RBG LED
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Current limited by resistor
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Light intensity regulated by PWM (Pulse-Width
Modulation)
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PWM frequency at least 50Hz
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Recommended at least 100Hz
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PWM can be generated in software
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Hardware generated PWM is expected
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Depends on hardware architecture
PWM on STM32F103
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4 timers
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Each has 4 channels
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Channels of one timer have the same period and phase
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Channels are connected to GPIO PINs
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Timer can use internal or external clock source
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System clock is 8 - 72 MHz
PWM on STM32F103
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Timer has 16-bit counter register and a Prescale
register
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One of possible modes of operation is PWM
PWM on STM32F103
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Auto-Reload Register (ARR) determines period of PWM
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Capture Compare Register (CCR) determines the duty
cycle
PWM on STM32F103
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PWM Frequency
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PWM Duty Cycle (%)
LED Matrix
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Matrix of 8x8 LED diodes
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Stackable modules
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Driver MAX7219
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Acts as a shift register
7-segment LED display
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8 LEDS in one package
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Many sizes
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Beware of maximum current
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Both variants – common cathode and common anode
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Limit number of pins → shift register
Shift register
NeoPixel LED
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3 LED diodes (RGB)
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3x8 bit
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Simplified shift register
(Data_IN, Data_Out)
Fixed timing
LCD
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Traditional, might seem to be a bit old-fashioned
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2x16 or 4x20 characters
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Based on Hitachi HD44780 chip or clones
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4 or 8 bits for data + 3 control signals
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Commonly used with I2C converter
TFT
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Matrix of pixels
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Various sizes (in inches and number of points)
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Commonly with SPI interface
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Many modules equipped with touch screen
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Touchscreen has standalone SPI interface
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Example: ILI9341
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2.4“ 240x320 pixels
OLED
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Small modules, typically
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0.91“ (128x32 pixels)
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0.96“, 1.3“ (128x64 pixels)
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Single color, twocolour a bit tricked
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I2C or SPI interface
e-Paper
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E-paper or e-ink
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Can keep the image even if powered off
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Better to blank the screen after couple of days
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Small modules for reasonable price 200x200 points
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Single or dual color
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Suspicious cheap → probably without driver
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SPI interface
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Beware of image size
Environmental sensors
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Temperature
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Relative humidity
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Barometric pressure
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Concentration of gasses
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Concentration of dust particles
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Intensity of light
Temperature
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Analog – PT100/PT1000, NTC, ….
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Dallas DS18B20
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NXP LM75
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TI TMP112
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Sensirion SHT30, SHT31, SHT35, SHT45, ….
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Infrared termometers and pyrometers
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Part of humidity and/or barometric pressure measurement
DS18B20
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Interface 1-Wire
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Unique ID
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Package TO-92, SOIC-8, or hermeticaly sealed
NEXPERIA LM75A
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General purpose chip temperature meters
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Resolution of 0.125 °C
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I2C interface
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Similar devices from TI (LM75A) or Analog Devices
(ADT75A)
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SO8 / TSSOP8 / MSOP8 / … package
Texas Instruments TMP112
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Miniature termometers
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SOT563 package (1.2 x 1.6 mm)
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Measurement on PCBs and in electronic devices
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I2C interface
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Alert on treshold (SMBus ALERT function)
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Similar models TMP101, TMP102
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TMP114 in package Picostar (0.76 x 0.76 mm)
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TMP117 in packge WSON / DSBGA package
Sensirion
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Swiss manufacturer of sensors
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SHT series includes humidity sensors
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Similar to TI TMP series
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SHT4x about 1.5x1.5mm 0.4uA
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Used mainly on PCBs
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Interface I2C
Infrared sensors
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Contactless measurement
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Industrial, building automation, medical
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Many types and modules
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Output analog, I2C, PWM
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Example: Melexis MLX90614, MLX90615
Barometric pressure and combined
sensors
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Robert Bosch GmbH
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One of few chip manufacturers in Europe
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Interface I2C
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BMP180 – just pressure
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BMP280 includes temperature
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BME280 adds humidity
Humidity sensors
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DHT-11 / DHT-22
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Temperature and relative humidity
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Specific serial protocol similar to 1-Wire
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Not compatible with Dallas 1-Wire
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16 bit relative humidity, 16 bit temperature, 8bit
checksum
Gas concentration
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Carbon dioxide
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Carbon monoxide
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Combustible gases
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Commonly long pre-heat time
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Frequently analog output
Gas concentration
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MQ-7 – Carbon monoxide
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MQ-2 – Combustible gas
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Carbon dioxide MG811
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Carbon dioxide NIR based
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MH-Z19B – UART/PWM
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SDC30 - UART/I2C/PWM
Dust particles
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Sharp GP2Y1010AU0F
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Based on light reflected from dust particles
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Analog output
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Sensirion SEN54-SDN-T
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The same principle
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Interface I2C
Light intensity
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A lot of analog devices
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BH1750
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I2C
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0 - 65535lux
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Precision and callibration
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VEML7700 (Vishay)
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I2C
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0 - 120000lux
Proximity measurement
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PIR
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Ultrasound
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Lidar
PIR - Pyroelectric (passive) InfraRed
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Motion sensor
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Surveillance
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Binary output
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Some delay
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Various angle and reach
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Many types: HC-SR505, HC-SR501, AM312
Ultrasound
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Distance measurement
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Originaly parking sensor in cars
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Many new applications
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Reach about 4 m, resolution 0.5 cm
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Trigger pin sends 8 x 40 kHz pulses
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Echo pin receives reflected signal
Ultrasound
Ultrasound
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Speed of the sound in air 340m/sec
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Obstacle in distance 1m:
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Time the signal travels from sensor to obstacle =
1/340 s = 2.9 ms
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Signal roundtrip time = 5.8 ms
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Distance in cm = echo pulse width in μs/58
Lidar
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VL53L0X
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I2C interface
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Same principle as ultrasound sensor
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Same reach and precision
Doppler radar
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RCWL-0516
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Movement detection up to ~ 8m
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Competitor to PIR sensors
GPS
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Most commonly used module NEO6M / NEO6Mv2
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Antena on uFL connector
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UART and PPS interface
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Serial text based protocol
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NMEA 0183 Standard For Interfacing
Marine Electronic Devices, Version 2.30
GPS
Gyroscope + Accelerometer
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Most popular solutions based on InvenSense MPU6050
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3-axis gyroscope and accelerometer
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Gyroscope: + 250 500 1000 2000°/s
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Accelerometer: ± 2 ± 4 ± 8 ± 16g
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16-bit ADC
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Interface I2C
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Alternative MPU6000 – SPI interface
Inertial sensor with magnetometer
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InvenSense MPU9250
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Similar to MPU6050
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Added magnetometer = electronic compass
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Interface both I2C and SPI
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Position expressed in angle coordinates: yaw, pitch,
and roll
Angle coordinates
Direction cosine method
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It is necessary to align output of sensor to the Earth
coordinate system and orient it to north pole
Direction cosine matrix
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Offset compensation
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Optionally, Kalman filter for data smoothing
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Euler angles, DCM computation
Biometric sensors
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Fingerprint
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Heart rate
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EKG
Fingerprint
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Will be part of followup lecture „IoT Security“
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Commonly, UART interface
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Main manufacturer of simple components is Synochip
Heart rate
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Chip Maxim Integrated MAX30100
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Includes oxymeter
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IR LED: 880nm
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RED LED: 660nm
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Interface I2C
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Low power consumption
EKG
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Based on Analog Devices AD8232
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Analog output
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Software for Arduino available
Data Storage
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uSD
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Flash
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EEPROM
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eMMC
uSD card reader
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A lot of simple and cheap modules
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Interface SPI
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Filesystem FAT32
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Software libreries exists, though the FAT is simple
enough
Flash
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Block organization, no filesystem
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SPI interface
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Larger capacity than EEPROM and smaller than SD
cards
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Popular module W25Q32 – 32MBit = 4MByte
eMMC
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In some sense successor of uSD
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About the same capacity
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More solid mechanical connection
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Used instead of uSD in several Something-Pi
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Reader in uSD format
Unsorted
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RTC
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Converters
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Multiplexers
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ADC
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NFC card reader
RTC
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With few exceptions, MCUs used in IoT don’t have real
time clock
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Several external RTC exist
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Battery keeping the time
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Interrupt sometimes on exotic voltage level →
additional electronics needed to wake-up MCU
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I2C interface
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PCF8563, DS3231
Thank you for your atttention!
Questions and comments?