EMBEDDED SYSTEMS BASICS WORKSHOP by ELC Skyward SKYWARD - - PowerPoint PPT Presentation

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EMBEDDED SYSTEMS BASICS WORKSHOP by ELC Skyward SKYWARD - - PowerPoint PPT Presentation

Jan 31, 2024 17 likes •582 views

EMBEDDED SYSTEMS BASICS WORKSHOP by ELC Skyward SKYWARD EXPERIMENTAL ROCKETRY SKYWARD EXPERIMENTAL ROCKETRY Who we are? SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS 2 Our Purpose Skyward Experimental Rocketry is an active student

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SKYWARD EXPERIMENTAL ROCKETRY

EMBEDDED SYSTEMS BASICS

WORKSHOP by ELC Skyward

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

SKYWARD EXPERIMENTAL ROCKETRY

Who we are?

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

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Our Purpose

Skyward Experimental Rocketry is an active student association operating inside Politecnico di Milano, it was born in 2012 with the ambitious goal of designing and realizing small and medium sized experimental sounding

  • rockets. Our project takes on from the passion of its founders and their desire

to challenge other similar associations active in Europe. The context we are in is very competitive and stimulating: our goal is to beat the altitude record achieved by an experimental rocket (32300m – HyEND – University of Stuttgart, Germany), and to do this we are following a program divided in different steps, each one involving new development and technological solutions.

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

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Our Workgroup: ELS

The electronic system has been designed and assembled entirely within the association, and will handle real-time recording and transmission

  • f data during launch.

The electronic system consists of a motherboard, which will coordinate all subsystems, each of which is controlled by a series of dedicated daughter-boards. The firmware on the microprocessors has been developed by our software engineers and it is designed to make the most of the hardware redundancy present onboard.

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SKYWARD EXPERIMENTAL ROCKETRY ROCKSANNE 2-ALPHA

Anakin Board Stormtrooper Array

Distributed System

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The whole system has been designed in the aim of modularity and flexibility.

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SKYWARD EXPERIMENTAL ROCKETRY ROCKSANNE 2-ALPHA

Distributed System - Flowgraph

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

PHASE 0: BASICS

What is an embedded system?

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

Why Embedded Systems ?

  • HW / SW for Special Purpose

○ Optimized for specific tasks ○ Sensors/ Microprocessor/ Actuators

  • Specific Constraints

○ Real Time / High Efficiency ○ Failsafe ○ Power Consumption ○ Structural

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GPS IMU LCD ALARM GPS IMU MOTORS LEDS

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

Embedded System - Nosecone Array

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POWER SYSTEM PRESSURE GPS THERMAL CUTTER CORE SYSTEM GSM TEMPERATURE STRAIN GAUGES SENSORS ACTUATORS

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

Our Design Purpose - Air Conditioning System

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SENSORS ACTUATORS MICROCONTROLLER

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

PHASE I : SPECIFICATIONS

Let’s define the proper hardware

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

Our Requirements

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TEMPERATURE HUMIDITY FSR 0 - 40 [°C] 0 - 100 [%] RESOLUTION 1 [°C] 1 [%] ACCURACY 2 [°C] 5 [%] SAMPLING FREQUENCY 0.1 [Hz] 0.1 [Hz]

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

Sensors Parameters

TRANSDUCER PROPERTIES

  • Range
  • Sensitivity
  • Resolution
  • Accuracy
  • Response time
  • Precision
  • Offset / Linearity / Hysteresis / Dynamic Linearity

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

LM75 - temperature sensors

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(125-(-55)) / 2^9 = 0.35 [°C] 1/300ms = 3.33 Hz

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

Sensors - Other Parameters

  • Supply Voltage (and current consumption)
  • Connectivity (Analog or I2C/SPI/UART)
  • Package

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

Sensor Connectivity - Digital Busses

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  • UART
  • I2C
  • SPI

3 or 4 wire

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

Sensor Connectivity - Analog Front End

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SENSORS GAIN + FILTER AMUX + ADC

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Package - IC

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THT: Through-Hole Technology SMT: Suface-Mount Technology

  • SIP: single in-line

DIP Lead pitch: 1inch = 2.54mm

  • QFN: Quad Flat No-leads
  • SOIC: Small outline IC

0.050 inch (1.27mm)

  • TSSOP: thin-shrink small
  • utline package

(pitch < 0.050 inch)

  • TQFP = thin-quad flat pack

( p about 0.5mm)

  • BGA: Ball Grid Array
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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

Package - others

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THT: Through-Hole Technology SMT: Suface-Mount Technology

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

BME 280 - Humidity parameters

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

BME280 - Electric Parameters

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

Microcontroller - PIC18F26K22

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

PHASE II : SCHEMATICS DESIGN

Let’s connect all the components

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

Power Section - RT9080

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  • LDO: Low Dropout Voltage
  • Fixed Output / Adjustable

RT9080:

  • Vout Fixed: 3.3V
  • MAX Input Voltage Range: 1.5V - 5.5V
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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

Other Voltage Regulator - DC:DC converter

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LDO DC:DC Accuracy High Low Linearity High Noisy Efficiency P = Iout (Vin-Vout) 80 - 95 %

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  • Uses the mechanical resonance of a vibrating

crystal to create an electrical signal with precise frequency

  • External / Built-in
  • Special Layout needed

Oscillator

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Decoupling\Bypass Capacitors

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  • Transient in current drawn by a particular

device, decoupling capacitors provide a local source of charge so that current can be supplied quickly without causing the voltage

  • n the power pins to dip suddenly.
  • These capacitors are connected between

power and ground to help stabilize the voltage delivered to active digital devices..

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Backup Capacitors

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Pull-up/Pull-down Resistors

An old wise man once told us: "I've never saw a resistor being afflicted by segmentation fault"

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  • Ensure the right logic level even if the

devices are in Hi-Z state or disconnected

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Headers - connectors

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RS485 STRAIN GAUGES THERMOCOUPLES MAIN POWER USB POWER ICSP GENERAL PURPOSE

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

(many) LEDS

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

PHASE II : PCB DESIGN

Let’s define where to place these components

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

  • Make the electrical interconnections between

components

  • Mechanical Supports for components
  • Many layers:

○ Metal (signal and power) ○ Dielectrics (separation)

PCB: Printed Circuit Board

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PCB REALIZATION

With Altium Designer 16

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Components Library Schematics PCB Design

What we will see...

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Mask Realization

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Etching

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

PHASE V : FIRMWARE

Quick overview of Real Time Mission Critical Software

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Real Time Mission Critical Software

RealTime:

software which fails if a timing deadline is not met.

  • Digital audio system
  • Control application

Mission Critical:

software whose failure might cause catastrophic consequences (death, damage to property, financial losses, etc.)

  • Medical radiation device
  • Nuclear reactor safety system
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Real Time Mission Critical Software

+

RealTime Mission Critical

=

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Real Time Mission Critical Software

  • Car’s airbags
  • Space and Aviation navigation system
  • Military applications
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Real Time Mission Critical Software

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  • A control software for a Nuclear Power Plan need to

sample the temperature of the core and maintain it at the required set point.

  • The temperature may be sampled at fixed ratio and

need to be processed as soon as possible.

  • Many other sensor need to be monitored in order to

discriminate

  • False Positive and Real Emergencies.
  • Redundancy are even in software for example different

control algorithm to perform the calculation and a voting system to thrust the results.

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Software Development Methodology

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AGILE

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Software Development Methodology

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AGILE

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Software Development Methodology

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  • Agile doesn’t fit very well for this
  • All requirements need to be covered
  • Usually is not possible or not safe to

patch a released system

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Software Development Methodology

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How a real time software looks like:

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  • Limited Time/Memory

Task

  • Real Time Scheduler
  • Low level Driver
  • Interrupts
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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

How a real time software looks like:

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Scheduler

  • Periodic and Aperiodic

Task

  • Many strategy

(Rate-monotonic, EDF, Round Robin etc)

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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

How a real time software looks like:

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Common problems

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Producer Consumer

  • One or more source of data (for

example sensors)

  • FIFO queue storing temporary

data waiting to be processed.

  • Asynchronous flow

Skyward use case: We use this solution because some boards are interconnected via CanBus. There is no master/slave so two or more boards can try to send data at the same time. If a collision occurs the second board will try a retransmission as soon as the bus is free. Using a queue we can buffer data and send it later.

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Common problems

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Memory Fragmentation

  • NO MALLOC (at least after the

initialization phase)

  • Dynamic allocation causes

memory fragmentation

  • Long running programs can

suffer

  • Non deterministic

defragmentation

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Common problems

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Memory Fragmentation Solution: Memory Pools

  • Fixed size queues
  • Deterministic behaviour (what

to do if the queue is full?)

Skyward use case: Fixed queues. Avoid dynamic allocation.

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Common problems

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  • Can be > 1s
  • Even on good SD card
  • Need to minimize the

number of write access

Slow I/O (Example SD Card)

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Common problems

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  • One buffer is filled
  • The other is processed
  • When the second is empty just swap

Slow I/O Solution: Double Buffer

Skyward use case: We use double buffering for logging our sensors to SD card on our main board.

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Conclusions

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  • Rigorous specification and continuous review and team communications
  • Keep it simple ( less code => less tests => less bugs)
  • Ask to yourself multiple times: How things can fail? How can I prevent and if not what

I can do to recover from failure?

  • Good specification => Good design => Good product
  • It doesn’t matter if you are making a rocket, a car or an air conditioner… have fun!
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SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEMS BASICS

JOIN US!

WWW.SKYWARDER.EU

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