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DT > Technical Understanding 2 > Flashcards

Technical Understanding 2 Flashcards

1
Q

what is a structure

A

a structure is a collection of parts which provides support and rigidity for the range of static and dynamic forces applied

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2
Q

definition of mass

A

describes the amount of material the object contains, kg

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3
Q

definition of weight

A

is the force of gravity pulling down on the object, N

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4
Q

definition of force

A

Describes the load put on an object, N

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5
Q

what is a static force

A

A static force is a load which is always present and does not move or change in magnitude
e.g. weight of the flagpole and the downward forces applied by Guy Lines

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6
Q

what is a dynamic force

A

A dynamic force is a load which may move and change in magnitude or direction during use

e. g. when a flag is raised up the flagpole using a pulley
- these forces are hard to predict so engineers take their ‘best guess’ based on research of similar structures

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7
Q

Types of forces: a tie

A
  • it resists a tension force and will fail by snapping

- this is reduced by making it thicker or making it from a stiffer material

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8
Q

Types of forces: a strut

A
  • it resists compression and will fail by buckling

- this is reduced by making it shorter or bracing it

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9
Q

Types of forces: a beam

A
  • it resists bending and will fail by the bottom surface cracking under tension
  • this is reduced by making it shorter or change the cross-section
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10
Q

Types of forces: a torsional force

A
  • a torsional force can cause a member to twist

- this can be reduced by shortening, making it stiffer or by changing the cross section

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11
Q

Types of forces: a shear force

A
    • they are scissor-like forces which try to slice through a component
  • this can be reduced by using a stronger material or by changing the cross section
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12
Q

what can you do to increase rigidity

A
  • change the cross - section
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13
Q

what are resistors used for?

A
  • to control current flowing in parts of a circuit
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14
Q

what are capacitors?

A
  • store an electrical charge, capacitance is measured in farads (F)
  • different types:
  • smaller ones are ceramic/polyester, not polarised.
  • Bigger ones are electrolytic and are polarised so the positive and negative leads must be the right way round, the positive lead is longer
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15
Q

what are diodes?

A
  • they are ‘one way’ components, only allow current to flow through them in 1 direction (polarity conscious)
  • They are used to protect other components e.g. if user connects battery the wrong way round, they prevent the flow of electricity
  • They prevent current flowing backwards and remove ‘back emf’
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16
Q

power supplies for electronic systems

A
  • power supply unit (PSU) or ‘plug top’ power supply
  • provides a steady voltage while pushing current through a system
  • Battery capacity (mAh) = current (mA) x time (h)
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17
Q

outputs - light

A
  • LEDs, in packages known as displays

- require a resistor to limit the current

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18
Q

outputs - sound

A
  • micro-controllers produce sound signals

- piezo - electric sounder is used to convert electronic signals -> sound waves

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19
Q

outputs - motion, solenoid

A
  • reciprocating, short stroke
  • on/off using driver
  • door lock release, pneumatic valve
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20
Q

outputs - motion, DC motor

A
  • rotary, high speed
  • speed control using PWM (pulse width modulation) output from micro controller, direction control using a motor driver IC
  • cooling fans, robots, automatic doors
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21
Q

outputs - motion, servo motor

A
  • oscillating, turns to an angle then stops
  • PWM control from a micro controller
  • robotic systems
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22
Q

outputs - motion, stepper motor

A
  • rotary, turns through precise angles, step-by-step
  • 4-wire control from a micro controller through a driver IC
  • CNC machines
23
Q

outputs - motion, brushless motor

A
  • rotary, high speed, high torque
  • PWM control from a micro controller through an electronic speed controller (ESC)
  • flying drones
24
Q

outputs - motion, piezo actuator

A
  • reciprocating, very short stroke
  • varying a voltage produces small linear movements
  • focusing systems in miniature cameras
25
Q

what are 7-segment displays

A

e.g. clocks/displays, controlled by micro controllers

26
Q

Multiplexing

A

reduces the power consumption of large displays and reduces the large no. of wires needed by displaying only one character at a time and then switching this off before displaying the next, and so on

27
Q

Alphanumeric displays

A

for detailed info either liquid crystal displays or LED

28
Q

converting between analogue and digital signals

A
  • each analogue input pin on a microcontroller contains an analogue-to-digital converter (ADC)
  • the ACD generates a range of numbers (8-bit ADC = 2^8 = 256 levels so ranges from 0 - 255 , 255 - 1 for full scale value)
  • Input voltage / supply voltage x full scale value
  • sometimes you don’t want to use the full range e.g. running a fan between 20°C - 30°C and this can be programmed
29
Q

Pulse width modulation

A
  • PWM

- it is when some micro controllers produce an analogue output signal used to control the brightness of LEDs

30
Q

signal amplification

A
  • sometimes it will be necessary to amplify the voltage of small signals from sensors before putting them into the ADC to get a good range of output values
  • A driver does this; it amplifies the output current to a level where the device works properly (normal micro controller pins can’t supply enough current, few mA at most, to power things larger than an LED or buzzer)
31
Q

signal amplification: about drivers

A
  • simplest driver is called a MOSFET (metal-oxide-semiconductor field-effect transistor) used for simple on/off control
  • 3 leads: g (gate), s (source), d (drain)
  • diode is used to protect it from high voltage electrical ‘spikes’ called ‘back EMF’
  • Motor driver IC could be used instead for when reversing is required
32
Q

Open loop systems

A
  • The micro-controller has no way of knowing whether the desired result has been achieved
  • It predicts/guesses and requires a datum, achieved with a digital sensor (microswitch), where all other movements are made from, the system will move the output until it reaches the switch.
  • e.g. cordless drill, user pulls trigger part away down - reduced speed is achieved - drill is applied to work piece so it slows down - user pulls trigger harder to maintain speed since the system doesn’t realise that the drill has slowed down

trigger - micro controller - driver - motor

33
Q

Closed loop systems

A
  • sensor is used to monitor the output, feeds info back to the MC which adjusts the output
  • uses feedback, more precise but to complex for simple systems
  • e.g. oven, temperature sensor monitors temp., when desired temperature is reached, MC will cycle heater off-on-off to maintain it
34
Q

sub - system

A

a single system within a system as a whole e.g. MC

35
Q

systems thinking

A

a logical process which analyses the needs of the application and identifies the physical quantities that need to be monitored, and the devices that need to be controlled

36
Q

1st stage of producing a system diagram

A

Identify the output devices

  • Are outputs to be controlled digitally or in an analogue way
  • are there any display or sound outputs
  • determines whether any of the output devices require a particular type of control signal e.g. a servomotor requires a PMW output signal
  • decide whether a driver is required for each output
37
Q

2nd stage of producing a system diagram

A

identify the input devices

  • Determine what sensors are to be used
  • consider issues of calibrating the sensors
  • determine what kind of signal the sensors produce and how they will be interfaced to the microcontroller
38
Q

3rd stage of producing a system diagram

A

decide on what MC to use

  • how many I/O pins are required
  • Will the microcontroller interface satisfactorily to the input/output devices chosen
  • are you familiar with the programming language
  • what are the power supply requirements
  • is the microcontroller fast enough for the application
  • can the microcontroller handle the type of data being processed
  • does the application require data to be stored
39
Q

About sensing light

A
  • LDR

- analogue resistive

40
Q

About sensing temp.

A
  • thermistor - analogue resistive
  • analogue sensing IC - AR
  • Digital temperature sensor - I2C
41
Q

About sensing sound

A
  • microphone - analogue output (pre-amplifier required)/ Digital output (indicates yes/no presence of sound)
42
Q

About sensing infra red

A
  • IR sensor - Digital output for detecting the presence of a warm object e.g. a hand sensor for an automatic tap
  • PIR sensor - for detecting a moving warm object e.g. intruder detection
  • photodiode - for receiving IR serial data e.g. from a remote control unit
43
Q

About sensing strain/force

A
  • Force sensitive resistor (FSR) - analogue resistive - for an approximate indication of applied force
  • load cell (containing strain gauges) - for accurate measurement of force/weight (instrumentation amplifier required)
44
Q

About sensing position/distance

A
  • switch e.g. micro switch, reed switch, float switch - digital switch
  • Proximity sensor - Digital output
  • Hall effect - indicates the presence or strength of the magnetic field
  • reflective/slotted Opto switch -Digital output, indicates the presence of reflective object or an object has moved to block a light beam
  • potentiometer - analogue resistive, linked mechanically to a moving system
  • rangefinder sensor - ultrasonic or infrared devices which produce a measurement of the distance from an object
45
Q

About sensing rotation

A
  • reflective/slotted Opto switch - Digital output, can detect a reflective patch or the gaps in the slotted wheel as shaft rotates
  • gear tooth sensor - detects the individual teeth on the steel spur gear as they rotate
  • quadrature rotation sensor - indicates the direction and angle of a rotation of the shaft E.g. control knob applications
46
Q

About sensing angles

A
  • Potentiometer - analogue resistive, mechanically linked to a rotating system
  • angle sensor - produces a signal indicating the absolute angle of a shaft (0-360 degrees)
  • accelerometer - can be used to measure tilt angles in two axis by measuring the effect of gravity
47
Q

Digital switch sensor

A
  • just switches which open/close when a physical quantity changes e.g. float switch, magnetic reed switch, push switch
48
Q

Analogue/digital output sensor

A
  • analog output sensor will connect to an analog input pin on the microcontroller
  • Digital output sensor will connect to a digital input/output pin
49
Q

Data stream output sensor

A
  • produce a data stream output in which direct alphanumeric information is transferred to the micro controller, rather than a voltage signal
  • use software libraries to communicate with an input device
50
Q

networking

A

electronic systems which are part of a network can share data and tasks, control each other and receive updates when required. For networking to be successful, all devices on the network must agree on a communications protocol e.g. internet protocol (IP)

51
Q

2 types of devices that use networking

A
  • networked devices - exchange info through cables

- wireless devices - wifi, bluetooth, RFID, NFC

52
Q

The different types of networked devices

A

wifi - provides high speed data transfer

Bluetooth - provides point to point short range communication (airdrop)

RFID - Radio frequency identification allows data to be read from passive tags or ID cards e.g. swipe cards, passports, security tags

NFC - near filed communication, maximum range of 4cm e.g. contactless, patients wristbands in hospitals telling the nurse what dose of medication when.

53
Q

smart objects

A
  • networked devices, they can join a network and share their information with other devices on the network - Internet of Things (IoT)
  • the IoT offers powerful opportunities for devices to sense and control their surroundings and to act collaboratively with other devices and controllers
  • e.g. smart lights that dim when you leave the room, smart thermostats refer to the weather forecast, smart milk that the fridge can detect when it runs out and re - order the milk in your next grocery delivery

DT (9 decks)

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