Microcontrollers exam Flashcards by Jasper Sion

Characteristics of a PC computer

Fixed location
Linked to mains power
Extendable buses
Add memory
Add devices

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Examples of distributed control systems

Protection systems
Data housing
R&D
Education

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What is telemetry

Taking data from a distance and feeding it into a computer system

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Components in a microprocessor

CPU - brains of the operation, will be executing the code you have loaded on to it
ALU - optimised to carry out AND/OR/NOT operations
FPCP - optimised to carry out mathematical operations
ROM
RAM
BIOS - low level code (firmware)
ADC
DAC

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What is RISC and CISC

Reduced instruction set computer (microprocessor uses this) - 50/60 instructions
Complex instruction set computer - 500+ instructions

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Characteristics of microcontroller

Small, mobile, standalone, battery powered, fixed, can be embedded

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Differences between Harvard and Von Neumann

VN: Uses one memory unit for both instructions and data
H: Has separate memory units for instructions and data

VN: Uses one set of buses for both instructions and data
H: Has separate buses for instructions and data

VN: Commonly used in general purpose computers
H: Commonly used in embedded systems (e.g. digital signal processing)

VN: Enables a more flexible use of main memory, enabling the processor to run a variety of programs that aren’t necessarily known in advance
H: For systems with a predetermined use, instruction memory can be implemented as ROM which protects the programs from hacking

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4 advantages of Harvard

⏰️ Instruction and data can be accessed simultaneously
📝 Instruction and data memory can have different word lengths
🤖 Different technologies can be used to implement instruction and data memory
🧑‍💻️ For systems with a predetermined use, instruction memory can be implemented as ROM which protects the programs from hacking

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Name some microcontrollers

Arduino
Raspberry Pi

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Where is power indicator (1)

(2)

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Where is USB in (1)

(3)

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Board rate =

Bits per second

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Where is DC power in (power supply) (1)

(4)

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draw the diode bridge

(5)

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voltage drop of a diode

0.7V

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(6)

Time period = 0.1s
so t = 0.1
r*C = 0.01
7.6e^0.01/0.1

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Where does the battery go (Vin) (1)

(9)

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draw a zener diode

(10) doesn’t have line through the middle

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draw a circuit for a regulated voltage supply to a microcontroller

(12)

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Draw IV for zener diode

(11)

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(13)

Vr = Vin - Vz
Vr = 7-5.1 = 1.9
I = 1.9/100 = 19mA

Power in r = Iz^2 * r
=0.019^2 * 100 = 0.0361W

Pz = Vz * Ir
= 5.1 * 0.019 = 0.0969W

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identify which is harvard and which is von neumann

insert pic

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Draw SBD for the schematic

(13)

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What is pin 1 used for

It is a serial pin for if you did not want to use a USB cable

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(14) write psuedo code using an active low

logic is reversed, 0 means LED on and 1 means lED off

draw arduino circuit with a tilt switch

(15)

draw LED symbol

(16)

what is the forward voltage of bright red and what current does it need to work (17)

2-2.5 20mA

Draw an arduino schematic with a mechanical push switch and a capacitor in parallel with the 10k resistor. Calculate the size of the capacitor

(19) C = 0*10^-6

Draw schematic with BCD chip integrating a 7 seg display

(22)

# 3 write code to read a byte from digital input 0 and then output 0x79 to channel 0

diginByte0 = digitalRead(DI0) digoutByte0 = 0x79 digitalWrite(0, digoutByte0)

convert 0x79 to 7 seg display

letter E convert to binary and then apply to 7 seg display

what is a masking operation

bitwise AND the byte with a 1 where you are looking at and if the answer is the masking operation = true

how do you set a bit in a byte to 1

OR it with a 1 where the bit is and the rest of the byte is 0s

how to set a bit in a byte to 0

AND the byte with another byte which has all 1's except a 0 for the bit you want to change to 0 (its complement)

draw arduino schematic with a default on three leds with switch

(23)

code for a debouncing a push button

digin2 = read_digin(2) If digin2 ! = to old_digin2 then Wait 50 //wait 50 ms for signal to settle to avoid multiple triggers End if old_digin2 = digin2

draw a schematic using a relay output

(24)

draw a schematic with a 7 seg display

(25) with a matched resistor (need to calculate) and ground it

draw a schematic with a 7 seg display and a bcd

(21)

if ABCD on the BCD chip is allocated pins 2,3,4,5 then write the code to display the number 2 on the 7 seg display

digitalWrite(2,Low) digitalWrite(3,High) digitalWrite(4,Low) digitalWrite(5,Low) as a byte: Digout && 11110010

what does this mean (26)

there are 4 wires in this cable

(27)

(28) Pseudocode: (29)

If something is called a swittch it is

digital

sensors and transducer's are

analogue

what is a transducer

takes one signal and converts it into another e.g. converts 0-100 degrees to 0-5V

draw an arduino schematic with an analogue input (potentiometer)

(30)

current vs voltage signals sensors

current signals: wires can be as long as possible much more expensive

draw a variable resistor draw a light dependent resistor

(31)

pseudocode for reading analogue signal

int sensorVal = analogRead(A0)

write pseudocode if you have a temperature sensor which is 0-5 V = 0 - 100 °C,

rawTemp = readAnin(0) // reads in a bit value from the analogue input A0 realTemp = rawTemp * (100/255) // scale the bit value to a temperature in deg C

resolution for analogue to digital scaling =

range/255

write pseudocode using a deadband for a window opener

If realTemp > 24 then // if its too hot open a window openWindow Else if realTemp < 22 then // put a 2 deg C deadband around the switching closeWindow End if

analogue vs digital

analogue represents the real world better digital will always suffer from sample and hold quantisation errors

why are there no analogue outputs on an arduino

driving AO takes a lot of power It makes the board more expensive and complicated

scaling from digital to analogue if drive = 20%

*Reverse calc for inputs *If the drive to a motor is 0-5V for 0-100% drive *If the DAC is an 8 bit device *Then if the code wants to output 20% (=1V) *SpeedOut = 20 *AnalogOut = (20/100)* (2^8 -1) = 51

symbol for a motor

(32)

(33)

5V = 255 bits 3V = 253 * 0.5 = 153 bits motorspeed = 0 void loop() { delay(1000) /1s motorspeed = motorspeed + 1 anoutWrite(0) = (motorSpeed/100)*153

What is pulse width modulation

Modulating the width of a pulse to give quasi analogue control

what is a pulse

when something goes high low high low...

what happens when you increase the width of the pulse. include diagram

letting the motor see a higher analogue input because it is integrating between the pulses as the speed of the pulses is faster than the reaction time of the motor (33)

PWM has a

fixed frequency

speed when mark:space ratio is 100:0

100%

speed when mark:space ratio is 30:70

30%

what % duty cycle is analogWrite(255) on an arduino

100%

what % duty cycle is analogWrite(127) on an arduino

50%

what % duty cycle is analogWrite(0) on an arduino

duty cycle =

mark:space ratio

duty cycle is 70% =

70:30 M:S

resolution of a shaft encoder

360 / 2^(number of layers)

write gray code for 3 bits

000 001 011 010 110 111

draw a 3 bit grey code shaft encoder

(34)

draw a H-bridge circuit

(35)

draw a control system diagram for a heater (negative feedback)

(36)

what is hunting

when there is a time delay, it can cause the system to be constantly turning on and off

define hysteresis

the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a given magnetic field

draw the mechanical hysteresis graph

(37)

how to fix hunting

using a deadband

what is an open loop

does not have any feedback and therefore cannot correct any changes (unplugging a heater, turning off a tap)

what is a closed loop

does have any feedback and therefore can correct any changes

(38)

(39)

Yorkshire water scenario: explain d1,d2,d3

A radar sensor, set at a fixed height measures the reservoir water level, this is then converted to water depth by knowing the distance to the reservoir bottom

draw harvard and von neumann

last photo

always on - resitor is ... the switch always off - resitor is ... the switch

up down

why would you use a pull up or a pull down resistor

A pull up resistor is used to hold the signal high (+5V) as its default state, a pull down resistor holds the signal low (0V) as its default state

What is debounce and why does it happen?

Debounce happens as mechanical switches are imperfect, the ability of the contact to make a perfect connection instantly and hold that connection is not possible due to the surface finish and internal reactive spring mechanism

Draw a debounce circuit, including component values for a 100ms time constant

2nd last photo

Draw a circuit for a simple analogue input such as a temperature sensor

last photo

Suitable resistor values for Switch PTC (thermistor) Led

10k ohms 5k ohms 220 ohms

Microcontrollers exam Flashcards

(89 cards)