3 IoT Nodes Flashcards
Capacitive Sensor:
A change in capacitance with a change in the environment
ie liquids, humidity, acceleration, human contact
Resistive sensor:
Physical changes such as light, force, heat
Applications: touch screen, street lights, camera
4 types of actuators:
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
Noise: Exponential Smoothing
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
Describe a Node
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
Typical clock rate of a node’s processor
usually 8MHz, but sometimes 16MHz and above
Typical ram of a node
4-8kb of RAM (random access memory)
Typical flash memory of a node
128-256kb of flash memory.
Limitations of nodes
- 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
XM1000 Node Processor:
Processor: Texas Instruments, 16bit RISC (Reduced instruction set computing) archiatecture
62.5-ns Instruction Cycle Time
XM1000 Node Memory
116kb flash memory
8kb RAM
1mb external flash
XM1000 Node ADC & Interfaces:
ADC: 12bit resolution (8 channels)
Interfaces: UART, SPI, 12C, USB
XM1000 node accuracy
Humidity: +- 3% %RH
Temp: +- 0.4c
XM1000 node communication (transceiver) spec
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
What standard is used for IoT?
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)
What are the specs of IEEE 802.15.4?
Max data rate: 250kb/s
3 frequency bands incl 2.4GHz used by XM1000 (others: 868/915Mhz)
10m communication range
Discuss PHY and MAC in IEEE 802.15.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.
Describe Beacon & Non-beacon
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
Network topolgies
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.
What is a transfer function?
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
How would you describe a linear Transfer Function?
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)
How would you describe a non-linear Transfer Function?
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
Transfer Functions: what is a Polynomial Function?
f(x)
Anything with a whole number on the x ie f(x) = 5x(2(sq)
If we zoom out of a graph enough, which transfer function will grow faster on the y axis?
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.
Types of transfer functions?
Linear Polynomial Exponential Power Logarithmic
Transfer Function: What is resolution?
Describes the smallest increments of stimulus
Outputs change in small steps
Transfer Functions what is accuracy?
Describes how close the measurement is to the true value
Transfer Functions: what is precision or repeatability?
Describes the difference in results when measurements are taken repeatedly under the same conditions
What is a magnetic sensor?
Detects magnetic fields for measuring rotary movement
What is a inductive sensor?
- 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
What is a thermoelectric sensor?
- A creating of voltage when there is a different temperature on each side of an object
- For measurement of temperature
Whats a pyroelecric sensor?
Temp voltage generated from a certain material when heated or cooled
For human/ animal motion detection, flame detection, gas analysis
What is a sound level sensor?
Generation of electrical voltage signals with vibration of air
Two approaches: inductive (dynamic mic) and capacitive (condenser mic)
COmmon sensing app: sound meter
Describe the signals of sensors
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
Noise: What is a Simple Moving Average
A method to obtain samples from a set number of samples. Designed to take the most recent so that the average remains correct.
