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MobUbiq > 3 IoT Nodes > Flashcards

3 IoT Nodes Flashcards

1
Q

Capacitive Sensor:

A

A change in capacitance with a change in the environment

ie liquids, humidity, acceleration, human contact

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2
Q

Resistive sensor:

A

Physical changes such as light, force, heat

Applications: touch screen, street lights, camera

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3
Q

4 types of actuators:

A

Hydraulic: hydraulic power. Powerful/ slow
Pneumatic: compressed air, rapid deliver
Electric: uses electricity, versatile
Mechanical: use other mechanical energy

Uses:
Adding light, heat, sound
Moving objects
Displaying messages

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4
Q

Noise: Exponential Smoothing

A

Noise:

A class of auto regressive integrated moving average.
The output is contributed by the current and previously computed value

y[i] = ax[i-1] + (1-a)y[i-1]

y = output
x = input
ax[i-1] = smoothing factor, between 0 & 1
y = previous output
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5
Q

Describe a Node

A 
Power Supply
Microcontroller
Communications (transceiver)
Sensors & Actuators (w/ ADC)
Memory (program & data)

Radio Frequency (RF), USB, Wireless, Bluetooth.

Some have integrated sensors such as light & temperature

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6
Q

Typical clock rate of a node’s processor

A

usually 8MHz, but sometimes 16MHz and above

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7
Q

Typical ram of a node

A

4-8kb of RAM (random access memory)

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8
Q

Typical flash memory of a node

A

128-256kb of flash memory.

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9
Q

Limitations of nodes

A
  • Often in hostile places; airplanes, forests, battle field
  • Limited storage space and power (hard to change battery)
  • Limited computational power
  • Mobile networks inferior to wired
  • Arbitrary topology - nodes in a plane wont be in a fixed place so difficult to create encryption key amoung local niehgbourhood of nodes
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10
Q

XM1000 Node Processor:

A

Processor: Texas Instruments, 16bit RISC (Reduced instruction set computing) archiatecture
62.5-ns Instruction Cycle Time

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11
Q

XM1000 Node Memory

A

116kb flash memory
8kb RAM
1mb external flash

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12
Q

XM1000 Node ADC & Interfaces:

A

ADC: 12bit resolution (8 channels)
Interfaces: UART, SPI, 12C, USB

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13
Q

XM1000 node accuracy

A

Humidity: +- 3% %RH
Temp: +- 0.4c

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14
Q

XM1000 node communication (transceiver) spec

A 
RF Chip: IEEE 802.15.4 standard 2.4Ghz wireless module
Transfer rate: 250Kbps
RF power -25dBm ~0dBM
Range: ~120m outdoor
~20-30m indoor
Power consumption 17.4mA
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15
Q

What standard is used for IoT?

A

IEEE 802.15.4
Stanard used which specifies the physical layer (PHY) and medium access control (MAC) for low-rate personal area networks (LR-WAN)

Emphasis on low-speed, low cost, small packets, simplicity unlike Wi-Fi which focuses on higher bandwidths (and high power)

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16
Q

What are the specs of IEEE 802.15.4?

A

Max data rate: 250kb/s
3 frequency bands incl 2.4GHz used by XM1000 (others: 868/915Mhz)
10m communication range

17
Q

Discuss PHY and MAC in IEEE 802.15.a

A

PHY is the physical layer which manages the RF transceiver, channel selection and regulates energy usage and signal management functions

MAC is medium access control, enables transmission of MAC frames. An interface that manages access to the physical channel and network beaconing.

18
Q

Describe Beacon & Non-beacon

A

In MAC: mode…

Beacon:
Transmits beacon and keeps data syncronised
Uses coordinator to transmit data
All other nodes scan for beacon and use CSMA-CA to access Superframe

19
Q

Network topolgies

A

Point to point, star and mesh:

point to point - simple, low latency, bluetooth headphones

star - low latency, consistant, one hop, WiFi at home. Cant route around network should node fail, cant store data should gateway to internet fail.

mesh - complex, higher latency (slower), long range over buildings or campus’s (1000’s nodes). Uses Gateway, sensor node with routing and simple sensor nodes. Stores data even if connection to the internet goes, ie good for energy meters. Routes around network if one node fails.

20
Q

What is a transfer function?

A

A mathematical function representing the input-output relationship

Input: measured physical parameter ie heat/ light
Output: Electrical output signal

A TF describes system response of sensor

21
Q

How would you describe a linear Transfer Function?

A

A linear TF can be described as a straight line. Very unusual for a sensor.

S = a + bx

x = input
b = slope (sensitivity)
a = offset (or output where input is 0)
22
Q

How would you describe a non-linear Transfer Function?

A

An output from an input (sensor) that is not a straight line ie there is variation between the level and input and the output.

Appropriate functions should be utilised to describe the response:

Polynomial function
Exponential Function
Logarithmic Function
Power Function

Some sensors have multiple inputs

23
Q

Transfer Functions: what is a Polynomial Function?

A

f(x)

Anything with a whole number on the x ie f(x) = 5x(2(sq)

24
Q

If we zoom out of a graph enough, which transfer function will grow faster on the y axis?

A

In fact, it can be shown that this is true for ANY exponential function and ANY polynomial function with positive growth. The exponential function will eventually outstrip the polynomial function.

25
Q

Types of transfer functions?

A 
Linear
Polynomial
Exponential
Power
Logarithmic
26
Q

Transfer Function: What is resolution?

A

Describes the smallest increments of stimulus

Outputs change in small steps

27
Q

Transfer Functions what is accuracy?

A

Describes how close the measurement is to the true value

28
Q

Transfer Functions: what is precision or repeatability?

A

Describes the difference in results when measurements are taken repeatedly under the same conditions

29
Q

What is a magnetic sensor?

A

Detects magnetic fields for measuring rotary movement

30
Q

What is a inductive sensor?

A
  • A change to the amplitude of an emitted high frequency electromagnetic field of oscillations
  • For detection of metallic object & different metals
  • Common in vehicle detection
31
Q

What is a thermoelectric sensor?

A
  • A creating of voltage when there is a different temperature on each side of an object
  • For measurement of temperature
32
Q

Whats a pyroelecric sensor?

A

Temp voltage generated from a certain material when heated or cooled
For human/ animal motion detection, flame detection, gas analysis

33
Q

What is a sound level sensor?

A

Generation of electrical voltage signals with vibration of air
Two approaches: inductive (dynamic mic) and capacitive (condenser mic)
COmmon sensing app: sound meter

34
Q

Describe the signals of sensors

A

Sensors produce a series of digital signals

Signals may contain noise

Implementing complicated digital filters may not be desirable as complex and high power consumption

simple data smoothing may be sufficient to remove some noise

35
Q

Noise: What is a Simple Moving Average

A

A method to obtain samples from a set number of samples. Designed to take the most recent so that the average remains correct.

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