Quiz 2 Topics

Question 1

Cooperative Multitasking

Answer 1

the threads/tasks decide which tasks to do and for how long (this means potentially one task could run forever and prevent others from ever running)

Question 2

Preemptive Multitasking

Answer 2

the OS decides which tasks to do and for how long. Run by the scheduler, based on time and priority

Question 3

Scheduler Issues (timing of tasks and switching between them)

Answer 3

must consider the time it takes to switch between tasks.

if time to run tasks is small - waste time switching too often

if time to run tasks is large - slow response

Question 4

Threads

Answer 4

a function that runs inside of a program/process that shares memory with that process

every process has at least one thread but it can have multiple threads of different priorities

Question 5

Real Time OS

Answer 5

special operating system designed to give reliable timing.

minimizes task switching time

Question 6

Semaphore vs Queue

Answer 6

semaphore - thread safe, signals between tasks

queue - thread safe, passes data between tasks

Question 7

using vTaskDelay (or similar) vs dummy loops to burn time

Answer 7

vTaskDelay type functions allow the OS to use the ‘dead time’ to do something else, where as dummy loops just waste it.

Question 8

D/A converter

how to calculate its resolution

Answer 8

summing op amp

resolution =voltage range/[ (2^number of bits)-1]

Question 9

A/D converter - Single Slope

Answer 9

uses an integrator (to integrate reference voltage function), compares the measured value to the integrator output - records the time when those values are equal

very accurate, not as fast
used in multimeters

Question 10

A/D converter - Flash

Answer 10

uses big voltage dividers, compares measured value with each node in the voltage divider

very fast, limited resolution

Question 11

A/D converter - Successive Approximations

Answer 11

uses output from D/A converter (makes a guess) and compares to measured value. keeps “guessing” until it gets close enough to the input.

Question 12

Digital Input

Answer 12

discrete values, typically uses a voltage level of 0 to 5V

Question 13

Digital Input

Answer 13

discrete values

source - output a voltage, processor supplies power
sink - ground when switch is closed, requires external power

Question 14

Analog Input

unipolar and bipolar

Answer 14

continuous range of values

unipolar = 0 to +V
bipolar = -V to +V

use an opamp to amplify a small signal
use a voltage divider to decrease a large signal

Question 15

Analog Output

Answer 15

continuous range of values

also output using pulse width modulation
amplify using a power transistor

Question 16

PWM

Answer 16

uses transistor in full on or full off state to minimize the energy dissipated by the transistor

relies on dynamics of the system to smooth out switch effect

duty cycle % is proportional to effective output voltage

Question 17

Digital Encoders - absolute using binary

Answer 17

generates a unique code for each shaft position. When powered up, they do not require a reset cycle even if the shaft was rotated while the power was switched-off

Question 18

Digital Encoders - incremental

what is a quadrature

Answer 18

sends an A and B pulse output that has to be counted by an external controller. provides incremental counts relative to a “start” or “home” position.

quadrature - two tracks (A and B) that are 90 deg out of phase. this is important for bidirectional position sensing

Question 19

Doppler Radar

Answer 19

shoots a beam of radio waves at a moving object to measure speed. this places no load on the measured object, just measures the change in frequency that occurs when the object is hit with the radio waves.

ex: used in police scanners

Question 20

Tachometer

Answer 20

measure angular velocity

attach an electric generator to the end of the rotating shaft, the output of which is a voltage that is a function of the shaft’s angular velocity

Question 21

Magnetic Pickup

Answer 21

measures angular velocity

small magnet wrapped with a coil of insulated wire and placed in a metal case. when the end of the magnet is placed near a magnetic material (ex: rotating gear) the magnetic field changes and there is a pulse voltage induced in the coil. when the material is removed, there is a pulse of opposite sign. the pulse frequency is proportional to angular velocity.

Question 22

Stroboscopic Tachometer

Answer 22

measures shaft speed

produces flashing light at a user controlled frequency that is shined on a rotating shaft or pulley that has a mark on one position. the user adjusts the flash frequency until the mark appears stationary.

read out directly in rpm

Question 23

Piezoelectric Accelorometer

Answer 23

measures change in acceleration

consists of a housing mass, a preloading spring sleeve, and a piezoelectric sensing element that can generate charge. when subject to acceleration, the force on the sensing element is altered and it generates charge which is sensed with an amplifier.

Question 24

Strain Gage Accelerometers

Answer 24

measures change in acceleration

uses strain gages as the sensing elements. they have low natural frequency limits (way less than that of piezoelectric type), but they are way less expensive.