BASICS EMBEDDED SYSTEMS2017/06/06 · SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS 3 Our Purpose Skyward Experimental Rocketry is an active student association operating inside

SKYWARD EXPERIMENTAL ROCKETRY

EMBEDDED SYSTEMS BASICSWORKSHOP by ELC Skyward

SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS

SKYWARD EXPERIMENTAL ROCKETRY

Who we are?

2

SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS 3

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.


Our Workgroup: ELS

The electronic system has been designed and

assembled entirely within the association, and

will handle real-time recording and transmission

of 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.

SKYWARD EXPERIMENTAL ROCKETRY ROCKSANNE 2-ALPHA

Anakin Board Stormtrooper Array

Distributed System

5

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

SKYWARD EXPERIMENTAL ROCKETRY ROCKSANNE 2-ALPHA

Distributed System - Flowgraph

6


PHASE 0: BASICSWhat is an embedded system?

7


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

8

GPS

IMU

LCD

ALARM

GPS

IMU

MOTORS

LEDS


Embedded System - Nosecone Array

9

POWER SYSTEM

PRESSURE

GPS THERMAL CUTTER

CORE SYSTEM

GSM

TEMPERATURE

STRAIN GAUGES

SENSORS ACTUATORS


Our Design Purpose - Air Conditioning System

10

SENSORS ACTUATORS

MICROCONTROLLER


PHASE I : SPECIFICATIONSLet’s define the proper hardware

11


Our Requirements

12

TEMPERATURE HUMIDITY

FSR 0 - 40 [°C] 0 - 100 [%]

RESOLUTION 1 [°C] 1 [%]

ACCURACY 2 [°C] 5 [%]

SAMPLING FREQUENCY 0.1 [Hz] 0.1 [Hz]


Sensors Parameters

TRANSDUCER PROPERTIES

● Range

● Sensitivity

● Resolution

● Accuracy

● Response time

● Precision

● Offset / Linearity / Hysteresis / Dynamic Linearity

13


LM75 - temperature sensors

14

(125-(-55)) / 2^9 = 0.35 [°C]

1/300ms = 3.33 Hz


Sensors - Other Parameters

● Supply Voltage (and current consumption)

● Connectivity (Analog or I2C/SPI/UART)

● Package

15


Sensor Connectivity - Digital Busses

16

● UART

● I2C

● SPI3 or 4 wire


Sensor Connectivity - Analog Front End

17

SENSORS

GAIN + FILTER

AMUX + ADC


Package - IC

18

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

● SIP: single in-line DIPLead pitch: 1inch = 2.54mm

● QFN: Quad Flat No-leads

● SOIC: Small outline IC0.050 inch (1.27mm)

● TSSOP: thin-shrink small outline package(pitch < 0.050 inch)

● TQFP = thin-quad flat pack( p about 0.5mm)

● BGA: Ball Grid Array


Package - others

19

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


BME 280 - Humidity parameters

20


BME280 - Electric Parameters

21


Microcontroller - PIC18F26K22

22


PHASE II : SCHEMATICS DESIGN

Let’s connect all the components

23


Power Section - RT9080

24

● LDO: Low Dropout Voltage ● Fixed Output / Adjustable

RT9080:● Vout Fixed: 3.3V● MAX Input Voltage Range: 1.5V - 5.5V


Other Voltage Regulator - DC:DC converter

25

LDO DC:DC

Accuracy High Low

Linearity High Noisy

Efficiency P = Iout (Vin-Vout) 80 - 95 %


● Uses the mechanical resonance of a vibrating

crystal to create an electrical signal with

precise frequency

● External / Built-in

● Special Layout needed

Oscillator

26


Decoupling\Bypass Capacitors

27

● 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

on the power pins to dip suddenly.

● These capacitors are connected between

power and ground to help stabilize the

voltage delivered to active digital devices..


Backup Capacitors

28


Pull-up/Pull-down Resistors An old wise man once told us: "I've never saw a resistor being afflicted by segmentation fault"

29

● Ensure the right logic level even if the

devices are in Hi-Z state or disconnected


Headers - connectors

30

RS485

STRAIN GAUGES

THERMOCOUPLES

MAIN POWER

USB POWERICSP

GENERAL PURPOSE


(many) LEDS

31


PHASE II : PCB DESIGNLet’s define where to place these components

32


● Make the electrical interconnections between

components

● Mechanical Supports for components

● Many layers:

○ Metal (signal and power)

○ Dielectrics (separation)

PCB: Printed Circuit Board

33


PCB REALIZATIONWith Altium Designer 16

34


Components Library Schematics PCB Design

What we will see...

35


Mask Realization

36


Etching

37


PHASE V : FIRMWAREQuick overview of Real Time Mission Critical Software

38


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



+RealTime Mission Critical

=



● Car’s airbags

● Space and Aviation navigation system

● Military applications



42

● 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.


Software Development Methodology

43

AGILE



44

AGILE



45

● 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



46


How a real time software looks like:

47

● Limited Time/Memory Task

● Real Time Scheduler

● Low level Driver

● Interrupts



48

Scheduler

● Periodic and Aperiodic Task

● Many strategy (Rate-monotonic, EDF, Round Robin etc)



49


Common problems

50

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.


Common problems

51

Memory Fragmentation

● NO MALLOC (at least after the initialization phase)

● Dynamic allocation causes memory fragmentation

● Long running programs can suffer

● Non deterministic defragmentation


Common problems

52

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.


Common problems

53

● Can be > 1s

● Even on good SD card

● Need to minimize the number of write access

Slow I/O (Example SD Card)


Common problems

54

● 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.


Conclusions

55

● 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!

SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEMS BASICS

JOIN US! WWW.SKYWARDER.EU

56

Documents

BASICS EMBEDDED SYSTEMS2017/06/06 · SKYWARD EXPERIMENTAL ROCKETRY EMBEDDED SYSTEM BASICS 3 Our Purpose Skyward Experimental Rocketry is an active student association operating inside