physcom 2022 exam

What are the characteristics of SMT?

- solder joint forms the mechanical and electrical connection - connection does not use holes - denser layout - cheaper PCBs - improved frequency response

1. How does the current flow in a NPN transistor? 2. How does the current flow in a PNP transistor?

1. In an NPN transistor, output current flows from the collector to the emitter. 2. In a PNP transistor, output current flows from the emitter to the collector.

1. What is a transistor? 2. What are the three pins called? 3. Name a common transistor?

1. Like an electronic switch - It can turn a current on and off. 2. Base (b) (MOSFET gate), collector (c) (MOSFET drain) and emitter (e) (MOSFET source). 3. Fx. A common transistor is the "bipolar junction transistor" or "BJT".

1. What is a NPN transistor? 2. What is a PNP transistor?

1. NPN: positive voltage to the collector terminal and positive voltage to the base. reverse from PNP, will turn on when power is applied 2. PNP: positive voltage to the emitter terminal and a negative voltage at the base terminal. allows power when no power is given to base, but will turn off when power is applied to base.

What are the two ways of attaching electronic components to a PCB?

1. Surface mount (SMT) 2. Through-hole

Circuit diagrams: What are the 3 guidelines for layout?

1: The lowest voltage should be shown at the bottom, and the highest voltage at the top. 2: The information should flow from left to right. 3. Sensors and other input devices on the left, and outputs such as motors, LEDs, on the right

What is a crystal for a microprocessor clock waveform in need of?

2 ceramic capacitors with values between 15 to 33pF.

At what percentage infill does the strength return have diminishing returns?

50%

What is a capacitor? What is capacitance measured in? what can they be used for? what are the similarities with diodes? can you draw a circuit with a capacitor included? How can capacitors and resistors be combined.

A capacitor is a bit like a savings account. This element stores energy when times are good and electricity is flowing into the capacitor. When the current is removed, the capacitor releases its charge until it is got no charge left. This can be used for example to power a microcontroller. If the MC loses power for just a second the MC will restart, so, the capacitor can power the MC so it doesn't restart. circuit symbol is two paralell lines with space in the middle Capacitance (C) measured in Farads (F) • E.g. microfarads (µF) or picofarads (pF) or nanoFarads (nF) Total Charge = C * Voltage Capacitors and resistors can be combined to create filters that target specific frequencies. E.g. sub-woofer Applying the wrong polarity will destroy the capacitor All capacitors have a maximum voltage rating. • a capacitor should be selected so that its working voltage should be at least 50 % greater than the highest voltage to be applied to it. Ceramic capacitors have values ranging from a few picofarads to one or two microfarads, ( µF ) but their voltage ratings are generally quite low. Electrolytic capacitors are generally used when very large capacitance values are required.

What is an IMU?

A combination of accelerometer and gyroscope. Gives a complete understanding of a device's acceleration, speed, position, orientation and more.

How does the current flow in a transistor?

A current flowing from the base to the emitter "opens" the flow of current from the collector to the emitter. Flows from Emitter to Collector in PNP Flows from Collector to Emitter in NPN

What is a magnetometer?

A device to measure strength and direction of magnetic fields. Used for compasses in phones etc.

What is a diode? On a diode, what would be indicated by a grey marking at one end? Draw a circut using a diode

A diode is like one-way street allowing electricity flow in only one direction Used in preventing splashback Polarized • Two sides: cathode (-) and anode (+) • Electricity flows from + -> - Most diodes start to work when the voltage exceeds 0.7 Volts Looks like an arrow in circuit diagrams, with LED there's and arrow pointing away. LEDs can be found in all sort of devices Grey or black rings on diodes indicate the cathode side

What is an inductor?

A electronic component that processes the property of inductance, meaning it opposes change in current flow. When supplying an AC supply we can use the inductor to filter out the alternating current and only let DC to pass. An inductor can be used to filter out current spikes in a circuit. And is often used together with a capacitor(which is filtering voltage) to filter. They are used in transformers, motors and relays. Is also used in boost converters to increase the DC output voltage.

GYROSCOPE

A gyroscope measures orientation, using the principles of angular momentum. Gyroscopes are often combined with accelerometers for more robust motion- sensing. Gyroscopes can be used to help with stabilization and well as changes in direction and orientation. Unlike accelerometers, gyroscopes do not have a fixed reference, and only measure changes. The units of angular velocity are measured in degrees per second (°/s) or revolutions per second (RPS). Ignores gravity.

What is a gyroscope?

A gyroscope measures orientation, using the principles of angular momentum. They do not have a fixed reference like accelerometers. Measures in degrees per second

What is a MAGNETOMETER?

A magnetometer is a measuring instrument used to measure the strength and the direction of magnetic fields. Often used as compasses in consumer devices such as mobile phones and tablet computers.

What is a pull-up and pull-down resistor? Draw a circut using a pull-up or pull-down resistor

A pull-up or pull-down resistor can ensure that a pin is in a high or low state - Often used with switches A pull-up resistor is connected to VCC and a pull-down resistor is connected to ground. Often used in switches. The resistor allows a little amount of current to run though it, but when the button is pressed there is less resistance, and the current will those the button side instead. This is used when the MCU needs to see the button pressed. pulldown will be a high state when pressed a pull up will be a low state when button pressed. Pull-up resistor: - the input pin will read a high state when the button is not pressed - a small amount of current is flowing between VCC and the input pin (not to ground) - When the button is pressed, it connects the input pin directly to ground. The current flows through the resistor to ground, thus the input pin reads a low state.

What is a raft, brim and skirt?

A raft is a horizontal latticework under the model, often used with ABS. Used when something needs support underneath to make sure print in place works. A skirt is a line around the model. its used to make the printer establish a smooth flow. A brim is the same as the skirt, expect is touches the model, used when the surface area of the print is not enough to secure it to the print surface.

What is an LDR?

A resistor that is dependent on the intensity of light. Resistance decreases as light falls upon them.

What is the definition of a sensor?

A sensor converts physical signal into electrical signals that can be manipulated symbolically on a computer

What is a capacitive touch sensor?

A sensor that when two objects touch or is in proximity of each other, charge will flow between them. Detects changes in the electrical field around them. Good for low force touches

What is a transfer function

A transfer function is a mathematical transformation that scales the data from an input device. A transfer function that matches the properties of an input device is known as an appropriate mapping. For force sensing input devices, the transfer function should be a force-to-velocity function: • E.g., the force one exerts on the IBM Trackpoint isometric joystick controls the speed at which the cursor moves. Other appropriate mappings include position-to-position or velocity-to-velocity functions, used with tablets and mice, respectively. A common example of an inappropriate mapping is calculating a velocity based on the position of the mouse cursor • such as to scroll a document. The resulting input is difficult to control

What is a potentiometer?

A variable resistor. Used for position detection and linear user input. It consists of 3 terminal devices.

Which AVR is best for PWM signals?

ATtiny45 noget med clock sensitivity

What is some exampels of movement sensors?

Accelerometer, gyroscope and magnometers, all of which is not dependent on external infrastructure.

PULSE SENSOR (ANALOG)

Activity tracking Can be mounted multiple different places Small form factor Acceptable performance Can be easily tweaked When the heart pump the bloods veins expands and contracts, using infra red light the sensor measures how much light is reflected and the frequency.

What can a sensor sense?

Air pressure sensors Capacitive sensors Acoustic sensors Photoelectric and laser-based sensors Optoelectric sensors Pressure mat switches and strain gauges. Contact and non-contact (magnetic) switches. Vibration detectors. Infrared motion detectors. Active microwave and ultrasonic detectors.

ACCELEROMETER

An accelerometer is a device that measures proper or g-force acceleration. Accelerometers are often built into devices to detect the orientation. Sense either static or dynamic forces of acceleration. • Static - gravity • Dynamic - vibrations and movement. Accelerometers usually contain capacitive plates • Some attached to springs As the plates move, the capacitance between them changes. These changes can be used to calculate acceleration. Acceleration is measured in g • as a multiple of the acceleration caused by Earth's gravity. Another commonly used unit of acceleration is meters per second squared (m/s2). • Free- fall acceleration (1 g) is 9.81 m/s2

What is an actuator? Name some exampels of actuators and their uses

An actuator is a component that is responsible for moving a mechanism. Their source of energy can come from • Electric voltage • Hydraulic fluid pressure • Pneumatic pressure Exampels: DC motor Servo motor Stepper motor Solenoids

What is an electric circuit? Draw an electric circuit

An electric circuit is a closed loop containing a source of electrical energy (a battery) and a load (a light bulb)

What is an ADC?

Analog-to-Digital converter (build into an atmega)

WATER FLOW SENSOR

Basically a Hall Effect sensor with plastic... Good for specific use cases, and prototyping "Easy" to DIY Water mill, with a rotor spinning and calculating the water flow.

What is a BMS?

Battery management system A Bms is there to keep the battery safe. It is responsible for not over chargeing or over dis-chargeing. If more cells in a battery is is responsible for keeping them on the save voltage.

How can we sense indoor motion?

Bluetooth, Wifi, RF, magnetic positioning, Infra red.

How does eyetracking work?

By an infrared illuminant tracking the cornea of the eye by reflecting the light back from the eye and measuring the position..

What is a voltage divider? What is an LDR voltage divider? Draw both a voltage divider using resistors and a divider using LDR

Can be used to turn a large voltage into a smaller one, by using 2 resistors in series If R1 was 1.7kΩ and R2 was 3.3kΩ - a 5V input could be turned into 3.3V at Vout. V_out = V_in * (R_2/R_1+R_2) A Light Dependent Resistor (photocell) can be used as a light sensor because its resistance changes in varying light levels. Usually, the LDR has 1 MΩ resistance in total darkness and approximately 5.4 kΩ in bright light.

How to do capacitative sensing?

Can measure anything with different diaelectric than air • A piece of wire and a simple timer • A piece of wire and CapSense library • A specialized chip (like QT113) When a touch is detected, pin goes LOW

How can you track gestures?

Computer vision og gyroscope + accelerometers

DHT22 + DS18B20 (DIGITAL)

DHT22: Digital Temp + Humidity Lowcost Small form factor Precision is so and so... DS18B20: Digital Temp sensor (waterproof) Surprisingly precise ...Waterproof Durable and sturdy

What are decoupling capacitors?

Decoupling capacitors supress high-frequency noise in power supply signals High frequencies (kHz-MHz range) bypass the integrated circuit (IC), and run through the capacitor to GND If the power supply temporarily drops its voltage, a decoupling capacitor can briefly supply power

What are digital filters? High and low pass filters? MOVING AVERAGE?

Definition - a digital filter performs mathematical operations on a sampled, discrete-time signal to reduce or enhance certain aspects of that signal. Remove noise from a sensor signal Good at rejecting outlier values • Helps you to find out what value is the 'most seen value' The filter sorts the readings and chooses the center value Low pass filter • used to focus on a desired signal frequency • usually for smoothing • Lets the low frequencies pass through High-pass filtering is the opposite of low-pass filtering • you're left with all the noise and rapid changes Moving average: Used to smooth out a signal Simplified form of a low pass filter - • Low pass filter allows you to focus on a desired frequency • Moving average filter simply smoothes out Takes the average of the last "X" amount of readings and averages them to produce the output. You can change the size of the window (the number of previous readings that can be averaged together) if the window size is too large, there will be noticeable latencies. If the window size is too small, the signal will still be noisy

How much current do i need

Depends on the components in the circuit Check the datasheets of the components, and add up the total (its best to round numbers up) Or you can check with a multimeter, measuring the current going though the system when its running Motors, or LED strips are known for large current draw and would need a separate power supply not enough current = brown-out Circuit that includes: ATmega328 = 20mA 3 red LED's with 330 ohm resistor = 10mA pr LED 2 motors = 25 mA pr motor 20mA + (3 * 10mA) + (2 * 25mA) = 100mA

What is classification?

Determining which group an observation or sample belongs to. Can be used to categorize gestures. (machine learning)

How are MCUs used in interaction design?

Embedded in smart objects, IoT, mobile and wearable computing. They make the design and development faster and easier. Needs to evaluate what kind of MCU you used, as some MCU, had a weak internal clock, and will drift, where some offer better long term clock.

Name three different types of force sensors

FSR (force decrease with more pressure), flex(increase when bend), stretch(increase when stretched)

What is an FSR?

Force sensor, not reliable on the form of pressing object = smart.

Name the 3 different forms of touch

Force, capacitive and resistive

What is FDM?

Fused Deposition Modeling, the printer we have used

GSR SENSOR (ANALOG)

Galvanic Skin Response sensor Measures electrical conductance of skin Measures "strong emotion" Sweat Mounted to two fingers

What kind of communication protocols does our ATmega have?

I2C-bus (sends data between MCUs), SPI (bootload pins), and UART/USART(TX/RX, programming and monitoring the chip)

IMU

IMUs (which combine both accelerometers and gyroscopes) are used to give a complete understanding of a device's acceleration, speed, position, orientation and more. can optionally include magnetometer, to sense magnetic fields, used in compasses.

LINE BREAK SENSOR (ANALOG)

IR light sensor - analog value based on amount of IR light hitting it 3.3V and 5V. Small form factor - could be problematic and requires calibration The spy sensor, makes a "line" of infra red light, that if broken registered it. Often used in motion sensoring in alarms

Logic gate: What does the AND-gate checks for? 1. What is the output if input a is 1 and input b is 0? 2. What is the output if input a is 1 and input b is 1?

If both inputs (a AND b) are 1. 1. output is 0 2. output is 1

Parallel circuit: When are two components in parallel?

If components share two common nodes, they are in parallel. Where series components all have equal currents running through them, parallel components all have the same voltage drop across them They share the current, but with full voltage.

Why is slicer settings important for rapid prototyping?

It can be made faster, stronger etc. depending on what is to be tested

What is a sound detector and its outputs?

It has 3 outputs: binary sound detection, audio envelope and true audio output. They are independent.

What is a crystal? How does it work?

It is a clock input to your microprocessor. It tis measured in Hz, and when a voltage source is applied to a small thin piece of quartz crystal, it changes shape (aka the Piezo-electric effect). This shape change produces mechanical vibrations or oscillations which can be used as a waveform for a clock.

Logic gate: What is the definition of the XOR-gate?

It only gives out 1 if one and only one input is 1. Otherwise it will return 0.

What is a hall-effect sensor?

Magnetic sensors. Commonly used as a switch to turn on when magnets are nearby. Rated to work with different magnetic fields, measured in Gauss.

Batteries in Parallel

Meaning the capacity is increased. 2 2000mAh batteries will in parallel have a 4000mAh capacity. The voltage remains like if it is one battery. Batteries are wired in parallel when the positives are wired together and the negatives are wired together

What is an accelerometer?

Measures g-force acceleration, can be used to detect direction in devices.

What is a MOSFET? Draw a circuit using a mosfet. Compare to BJT. Descripe the different channels of MOSFET.

Metal Oxide Semiconductor Field Effect Transistor. The main principle of the MOSFET device is to be able to control the voltage and current flow between the source and drain terminals. It works almost like a switch and the functionality of the device is based on the MOS capacitor. The MOS capacitor is the main part of MOSFET. Has a drain, gate and source. There are both n and p channels MOSFETS. Same as NPN and PNP in BJT. BJTs are usually used for electrical currents of under one amp, while MOSFETs are typically used for higher-current applications.

What are the advantages of an MCU?

Micro-Controller-UNIT Reduces circuit size significantly, allows greater flexibility (can be reprogrammed).

What are the disadvantages of an MCU?

More expensive than other ICs (integrated circuit) and has limited storage etc.

OPTICAL DUST + CO2 SENSOR (ANALOG)

Optical Dust Sensor - GP2Y1010AU0F Lowcost So and so performance Useful in very specific contexts works by using infra red to measure how many particles are in the air MG-811 CO2 Sensor A bit tricky to work with Low cost air pollution "indication" Surprisingly expensive Not to scale works by using infra red light, and measures how much of the light is blocked by the co2 in the air

Describe the power formula

P (watts) = V (volts) x I (amps) P = V^2 ÷ R (Ω) P = I^2 x R

What is a Piezo sensor?

Piezo sensors are flexible devices that generate electric charge when they're stressed. This characteristic makes piezos an ideal solution for low-power flex, touch, and vibration sensing.

How do we use a decoupling capacitor?

Place the capacitor between the VCC and GND, parallel to the load. It should always be located as close as possible to the IC.

What can be used to rate the performance of a sensor?

Precision/resolution how close the values are grouped together and accuracy how close the values are to the true goal (skydeskrive). Usually multiple inputs is received and a mean is calculated.

What is PCB?

Printed Circuit Board You can create your own PCB by using chemical techniques to convert a copper-covered board into a custom-etched one. You can construct highly reliable, compact circuits. can also be milled with a fancy CNC machine.

How do we calculate resistors in parallel?

R_tot = (R1 * R2) / (R1 + R2)

What is a hall sensor?

Reacts to a magnetic field. The most common reaction, in Interactive Systems, being the sensor acting as a digital switch "turning on" in the presence of a strong enough magnetic field. Hall effect sensors are all rated to work with a specific strength of magnet field (measured in Gauss) which dissipates with distance from the magnet.

What is SLS?

Selective Laser Sintering,

What is the difference between analoge and digital sensors

Sensors measure a physical quantity and respond to it by producing an output such as a voltage. Analog sensors are those which produce an analog signal based on what they sense. Similarly, digital signals are those which produce a digital signal in response to what they measure at the input. Analog sensors output a signal that varies between 0-1 Dialog sensors output a signal that are 0 or 1 (low or high)

How do you calculate resistance? Both in series and parallel. Two resistors with resistance values 1.2 kilo-ohms and 2.2 kilo-ohms are connected in series. Determine the total resistance of the network. Two resistors are combined in parallel. If they have values of 100 ohms and 1.2 kilo-ohms, determine the value of their combined resistances.

Series: r_1 + r_2 + r_3 + r_4 Parallel: 1/R_T = 1/R_1 + 1/R_2 + 1/R_3 + 1/R_4 When you have only two resistors in parallel: R_tot =(R_1*R_2) / (R_1+R_2)

WATER LEVEL SENSOR (ANALOG)

Simple but rigid setup Works well! Unfortunately sparse info and datasheets online A water level sensor measures the amount of liquids in a closed container. measures the water pressure to calculate the water level.

What is a microcontroller? And what to consider when choosing one?

Small programmable chip holding memory and a processor. The brain of your circuit. How many pins do you need. Memory on the MCU. Clock speed (precision)

What types of acceleration can a accelerometer detect?

Static (gravity) or dynamic (movement)

What is a stepper motor? What can it be used for?

Stepper motors are good for position control. Steppers are a special segment of brushless motors. You can use them to incrementally "step" to the next position

SOUND DETECTOR

The Sound Detector has three different outputs: binary sound detection, audio envelope (changes in the sound), and a true audio output (e.g. human speech, music, natural sound). The 3 outputs are simultaneous and independent, so you can use as many or as few as you want at once.

Logic gate: What result does the NAND-gate give? 1. what is the output if the input a is 0 and the input b is 0? 2. what is the output if the input a is 1 and the input b is 0?

The opposite of the AND-gate. 1. output is 1. 2. output is 1.

Logic gate: What result does the NOR-gate give? 1. What is the output if the input a is 0 and the input b is 0? 2. What is the output if the input a is 1 and the input b is 1? 3. What is the output if the input a is 1 and the input b is 0?

The opposite of the OR-gate. 1. Output is 1. 2. Output is 0. 3. output is 0.

What is infill?

The structure that is printed inside the object OR The amount of air inside the solid structures from fusion (eg. walls) 90% means 10% of the room inside the wall is air

What are the main difference between a MOSFET and a BJT?

The terms current controlled device and voltage controlled device are ambiguous. Book by author Donald Neamen refers BJT as voltage controlled current device. BJTs are current-controlled devices. BJTs are switched on by a current going through the base of the transistor. MOSFETs are voltage-controlled. Voltage, not current, either turns the transistor on or off. (According to me, in case of BJT the output current NEEDS to be controlled by a continuous current I.The moving charge maintains the barrier. Say if base current in Common-source mode is made zero, you lose the control over BJT. Yes, this current Ib is controlling the voltage across the base-emitter junction and controlling it. Now in MOS, you control output current by application of a Voltage which results in charge accumulation at controlling gate. You see accumulated charge controls output. An accumulated charge independently creates a Voltage across gate. This controlling voltage can be stored permanently without any external help like in case of FLASH memories used in USB. So in one case a moving charge (current) and in other static charge (voltage) controls the output. This happens because in BJT the Base-Emitter junction conducts the charge of control current. However, in MOS the insulated gate doesnt allow current flow(neglecting leakage through dielectric).)

ELECTRET MICROPHONE

Tiny microphone, works best as binary switch Can be DIP (Dual in-line package) or with a board attached Competition: SparkFun/Adafruit boards and the MAX4466

Series circuit: When are two components in series?

Two components are in series if they share a common node and if the same current flows through them. They share the voltage, but with full current.

What is a resistive touch screen?

Two large transparent conductive overlays that vary in resistance

Describe Ohm's law and the relationships between current, voltage and resistance found in an electrical circuit.

Voltage(V)= current(I) x resistance(R) or I=V/R or R= V/I

Sensor data, what should we know?

What type of raw data comes from the sensor • Format • Type How to convert the raw data into something meaningful • Check the datasheet for conversions

What is a resistor? What is it used for? What kind of resistors exists? Draw a circute using a resistor. What is resistance measured in?

a component of an electrical circuit that has resistance and is used to control the flow of electric current. Can be used to limit the amount of current that will move through that circuit each second. Unit - Ohms (Ω) Different kinds of resistors: - Photocell -> to pile det peger ind mod sqiggely line - Thermistor - Potentiometer -> en vandret pil ind på sqiggely line - Flex sensor -> en skå pil igennem sqiggely line - force-sensitive resistor (FSR) -> en skå pil igennem sqiggely line

What is a switch? Draw a circut using a switch

a device that can interrupt the electrical flow in a circuit

What is a thermometer?

a device used to measure temperature. Reads with analog read.

How does a battery work?

batteries contain a liquid part inside which causes chemical reactions to happen when there are electrons being moved through it. Lihium polymer (Lipo Battery) Lithium ion (Li-ion battery)

What is a slicer?

converts 3d models into printable file-format. STL or mesh -> slicer -> g.code

Logic gate: What does the OR-gate checks for? 1. What is the output if input a is 0 and input b is 0? 2. What is the output if input a is 1 and input b is 0?

if either one of its inputs (a OR b) is 1. 1. output is 0 2. output is 1.

What is current? And what is it measured in?

the amount of electrical energy passing through any point in the circuit -> measured in amperes or amps (A) • Direct current (DC) and Alternating current (AC)

What is resistance? And what is it measured in?

the amount that any component in the circuit resists the flow of current -> measured in ohms (Ω) • All electrical devices resist the flow of current

What is voltage? And what is it measured in?

the relative level of electrical energy between any two points in the circuit (e.g. power and ground) -> measured in Volts (V)

What must be considered when choosing an input device?

• The physical sensor • Feedback • Ergonomics • Interplay between all of the interaction techniques Most devices sense: • Linear position • Motion, or force Rotary devices sense: • Angle • Change in angle • Torque This determines the mapping from input to output, or transfer function.