The following slides were used as an introductory support for the hands-on workshop on the STM32 Platform that was held on the Pervasive Systems course (La Sapienza University of Rome, May 2017).

1. Hands-on Workshop:
An insight over the STM32 Platform +
Presentation of a water-level & temperature monitoring
prototype
Presenter: Julio César Carrasquel
carrasquelgamez.1726154@studenti.uniroma1.it
Rome, Italy. May 2017.
Università degli Studi di Roma La Sapienza
Dipartimento di Ingegneria Informatica,
Automatica e Gestionale Antonio Ruberti (DIAG)

2. 2
Let me introduce myself
● Licentiate Degree in Computer Science from Central University of Venezuela.
Caracas, Venezuela. Former Software Developer at Wincor Nixdorf.
● Master of Science of Engineering in Computer Science at La Sapienza University of
Rome. Rome, Italy.
● Embedded Software Traineeship at INTECS Solutions SpA (Italian company
focused on embedded systems development for several sectors such as defense,
railway, and automotive among others).
● Some key interests: Embedded Software Development, Internet of Things, Computer
Networks, Service-oriented architectures, C/C++, Java.
● For additional info check out my LinkedIn profile:
https://www.linkedin.com/in/julio-césar-carrasquel-b5729844/

3. 3
About this presentation and acknowledgements
● The following slides have been prepared as an introductory support for the
hands-on workshop on the STM32 Platform that was held on the Pervasive
Systems course (La Sapienza University of Rome, May 2017).
● The slides provide a quick look-up over the STM32 platform. In addition, it
is introduced as a demo a prototype developed within a traineeship period at
INTECS Solutions SpA (Rome, Italy).
● Special thanks to Ugo Maria Colesanti (INTECS Solution SpA) for the
tutorship given throughout the traineeship, and professor Ioannis
Chatzigiannakis (http://ichatz.me/) for the opportunity provided.

4. 4
Key notions
● Embedded System: A computer system with dedicated functions within a larger
electro-mechanical system. They range from simple portable devices (wearables,
MP3 players) up to large complex systems (automotive, telecomunications,
avionics, space).
● Microcontroller: Small computer on a single integrated circuit. It includes the
processor, memories, and input/output peripherals. Core piece on an Embedded
System.

5. 5
ARM Architecture
● Set of specifications regarding the instruction set, execution model, memory
organization, instruction cycle, and more which describes a machine
implementing that architecture.
● ARM Cortex: Wide set of 32/64 ARM Architectures.
– Cortex-A: It stands for applications. Designed for hosting rich operating system
platforms (e.g. Linux, Android).
– Cortex-M: It stands for embedded. Processors optimized for the embedded
market (low cost, energy efficient, low-power).
– Cortex-R: Real-time. High-performance and very critical scenarios (reliability,
real-time response, for example: the automative world).
● ARM Holding is a British company that develops the architecture of ARM-
based product. Intellectual Property business model.

6. 6
STMicroelectronics and the STM32 platform
● STMicroelectronics is a French-Italian multinational electronics and
semiconductor manufacturer headquartered in Geneva, Switzerland.
● STM32 is a family of 32-bit microcontrollers developed by
STMicroelectronics. Based on the 32-bit ARM processor cores. Specifically,
in the ARM Cortex-M architecture.
● In particular, we work in this workshop with the STM32L476
microcontroller which belongs to the family of low-power microcontrollers.
● The STM32L476 MCU is placed within the Nucleo development board.
The Nucleo boards provide a medium for debugging and development with
the microcontroller units.

7. 7
The NUCLEO-L476RG Development Board
St-link debugger
User button
Arduino –
compatible
pins
STM32L476RG
MCU
User Led
USB Connector
Reset button
Expansion pins
32 kHz
External
crystal
● STM32L476 MCU:
– Based on the ARM Cortex M-4 Architecture.
– 1 MB Flash memory, 128 Kb SRAM Data Memory.
– Clock frequency: up to 80 MHz.
Debugger

8. 8
ARM Cortex M-4 Architecture
● 32-bits Harvard based architecture
● Thumb-32 instruction set (16/32 bits instructions)
● Core registers: R0...R12 general purpose, SP stack pointer, PC program counter,
LP link register, APSR program status register.
● Unified memory space 4GB
● On-chip bus interfaces: Based on the ARM AMBA (defines the communication
between the microcontroller modules through the on-chip buses)
– AHB (High-performance bus) connecting the MCU core elements.
– APB (Peripheral bus). Low-bandwidth connection with the peripherals.
● NVIC controller: Interruptions and exceptions management with priority
handling
● Systick timer (24-bit decrement timer).
● Optimized for low power consumption. Various sleep modes available.

9. 9
ARM Cortex M-4 Architecture
● Example of the ARM Architecture design. The system bus (AHB) connects the core
elements (processor, memories, debug interface) whereas the peripheral bus (APB) deals
with the connection of all MCU peripherals.
● Both bus channels are interconnected by a bridge managed by a Master-Slave mechanism
following the ARM AMBA specification.

10. 10
ARM Cortex M-4 Memory map
● Address space: 4GB, little/big endian

11. 11
STM32L476 Look-up
● The microcontroller is based on the Cortex M-4. However, as it has been shown, it has its
vendor own characteristics (clock frequency speed, memory, consumption, etc).
● Different clock sources:
– External 4-48 Mhz crystal oscillator (HSE)
– Internal 16Mhz factory-trimmed RC (HSI16)
– Internal 32 Khz low power RC (LSI)
– External 32 Khz crystal for RTC (LSE)
– Internal multi-speed 100kHz-48Mhz oscillator (MSI)
– System PLL (uses HSE,HSI16 or MSI) up to 80Mhz.
● A wide set of peripherals, for example:
– Timers (16-bit low-power, generic, basic, watchdog, Systick timer)
– ADC/DAC: Analog-to-digital, digital-to-analog converters.
– Several interfaces for communication: USART, SPI, I2C, CAN, etc.
– Configurable general-purpose input/output (GPIOs).

12. 12
Software development tools
● STM32CubeMX Tool
– Make an initial configuration of the
microcontroller features.
– Pin-out conflict resolution
– Clock sources configuration
– Peripherals setting
– C code generation
● System Workbench 4 IDE
– Eclipse-based integrated development
tool-chain
– Import generated code of the
STM32CubeMX
– Debugging features
– Connection with the Nucleo
development board

13. 13
Tank water-level & temperature monitoring system
● It was used the STM32L476RG as the the core piece for the development of a tank water-
level & temperature monitoring solution.
– For detecting water-level is used the HCSR04 ultra-sonic ranging device.
– For the temperature is used the water-proof DS18B20 thermometer.
● The system also includes an U-Blox NEO-6M GPS receiver which keeps track of the location
where the system is operating.
System schematic diagram

14. 14
Tank water-level & temperature monitoring system
Sensors used within the project
● NEO-6M GPS receiver device
– Connected to the MCU through a UART interface.
– Working with the NMEA 0183 standard.
● Water-proof DS1820 temperature sensor
– Measures temperatures between -55 °C and +125 °C.
– Managed by the 1-Wire communication bus mechanism.
● Ultra-sonic HC-SR04 ranging device
– – It sends 40KHz burst pulses which are reflected back by the
obstacle.
– It forwards through the echo-line a pulse whose width is
proportional to the distance towards the obstacle.
– Measuring range: 2 cm – 400 cm

15. 15
Tank water-level & temperature monitoring system
An additional look about how the HC-SR04 ranging device works
● For measuring the distance with respect to an obstacle (the water surface), is required to supply
through the trigger input line a pulse of 10 microseconds.
● Then, it will start the ranging sending out an 8 cycle burst of ultrasound at 40 kHz.
● Whenever the sensor receives the signal back, it will set a high pulse through the echo output line
whose pulse width will be proportional to the distance between the sensor and the obstacle.
● Finally, for calculating the distance between the module and the obstacle, the echo pulse width (in
microseconds) is divided by 58 which giving the distance in order of centimeters.

16. 16
Tank water-level & temperature monitoring system
● The HC-SR04 sensor is positioned at the top of the tank, and sends the ultra-sonic
waves towards the water surface where are immediately reflected back to the device.
● Thus, this mechanism can derive the distance between the device and the water
surface. Knowing in advance the tank height it can be calculated which is the
current tank water level.
Water tank with its associated levels and thresholds.

17. 17
Tank water-level & temperature monitoring system
Implementation of a system console for the monitoring system
● The monitoring system integrates a module embedded for managing a system terminal. The idea
is to provide a command-line interface for interacting with the user connecting the
microcontroller with the computer using an UART channel which goes over the USB connection.
● Through this interface the user can configure the system main variables (sampling period, turning
on/off devices, water-tank height and the different thresholds), receive the sensor measurements
and the corresponding alarms.

18. 18
● For getting more details about the developed prototype:
– Find the project source code freely available on Github:
https://github.com/juliocesarcarrasquel/waterlevel-monitoringsystem
– Download the system technical report on Slideshare:
https://www.slideshare.net/juliocesarcarrasquel/tank-water-level-
monitoring-solution-based-on-the-stm32l476-mcu
Tank water-level & temperature monitoring system

19. 19
Other useful references
● ST Microelectronics. STM32L476RG Microcontroller: Ultra-low-power with FPU ARM Cortex-M4
MCU 80 MHz. http://www.st.com/en/microcontrollers/stm32l476rg.html
● ST Microelectronics. STM32L476xx Datasheet: Ultra-low power ARM Cortex-M4 32-bit MCU.
Retrieved from: http://www.st.com/resource/en/datasheet/stm32l476rg.pdf
● ST Microelectronics. STM32CubeMX – STM32Cube initialization code generator.
http://www.st.com/en/development-tools/stm32cubemx.html
● OpenSTM32 Community Site. System Workbench for STM32.
http://www.openstm32.org/System+Workbench+for+STM32
● NEO-6 U-Blox GPS modules Datasheet. Doc. Number: PS.G6-HW-09005-E. Rev. E. December
2011.
● NMEA Data. Retrieved from: http://www.gpsinformation.org/dale/nmea.htm. (April 2017).
● Dallas Semiconductors Corp. Division of Maxim Integrated Products, Inc. DS18B20 Programmable
Resolution 1-Wire Digital Thermometer Datasheet.
● ElecFreaks. Ultrasonic Ranging Module HC–SR04 Datasheet. Retrieved from:
http://www.micropik.com/PDF/HCSR04.pdf (April 2017).

20. 20
Thanks for your attention!
Hands-on Workshop:
An insight over the STM32 Platform +
Presentation of a water-level & temperature monitoring prototype
Questions, comments and suggestions are welcome!
Presenter: Julio César Carrasquel
carrasquelgamez.1726154@studenti.uniroma1.it
Rome, Italy. May 2017.