User Interface Engineering FS 2013

Transcription

1 User Interface Engineering FS 2013 Input Fundamentals

2 Last Week Brief Overview of HCI as a discipline History of the UI Product perspective Research perspective Overview of own research as motivation Evaluation Design Prototype

3 Today

4 Buttons & Switches Buttons are everywhere Especially on interactive devices

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8 Bop It What s in it?

9 Bop It What s in it?

10 Electronics 101- The Basics - Just Enough to Scrape By Current, Voltage, Resistance Illustrations mostly from: Paul Scherz, Practical Electronics for Inventors Recommended Reading:

11 Current e e e e e e The amount of charge crossing an area per unit of time

12 Current e e e e e e I = ΔQ Δt = dq dt

13 Current Electric currents are carried by electrons Each electron carries a (negative) charge e = 1.6 x C Current is measured in Ampere (A) 1A = 1 C s e

14 e Direction of Flow Conventional current flow (I) e e e e e e e e - Battery + e YouTube: Oil Drop Experiment

15 Voltage Opposing charge distributions at a distance create electrical force between them Unit of positive charge will pushed by the positive and pulled by the negative distribution V When the charge unit moves it will change in potential energy Voltage is the amount of energy needed to move a unit charge from one place to another Potential energy Unit of charge 1V = 1 J C

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17 Voltage Reference Points 6V 3V V 0V + + Ground or 0V Reference - - 0V -3V

18 Resistance Reduction in current flow due to resistance in conductor All conductive materials have some resistance Measured in Ohm (Ω) Potential difference of 1 Volt will force a current of 1 Ampere through a resistance of 1 Ohm 1Ω = 1 V A

19 Resistance - Water Analogy

20 Resistor Symbol R

21 Ohm s Law Current through a conductor between two points is directly proportional to the potential difference across the two points I = V R V = IR R = V I Ohm's law states that the R in this relation is constant, independent of the current

22 Power The work performed by an electrical current as it runs through a circuit Measured in Watts P = V I 1W = 1VA

23 Basic Circuits

24 Series Circuits

25 Parallel Circuit

26 What s in a Switch?

27 Switches + - Interrupter Switch

28 Switches + - Two way diverter switch

29 Types of Switches Number of Poles Throws Duration of contact Long-term (Switch) Momentary (Button) Default Behavior for Push Buttons Normally Open (NO) Normally Closed (NC)

30 Single Pole Single Throw (SPST)

31 Single Pole Dual Throw (SPDT)

32 Dual Pole Single Throw (DPST)

33 Single Pole (n) Throws (SP(n)T)

34 Magnetic Reed Switch

35 Mercury Tilt-Over Switch

36 An interactive system Conceptual Overview Mechanical elements Enclosure Circuits Microcontroller Host-PC Sensors Actuators ADC DAC

37 Microcontroller Atmel ATmega328 Used in Arduino and other electronics frameworks

38 Arduino Pin Mapping

39 Arduino Board

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41 Connecting to a digital pin Switch closes/breaks circuit Problem? Input is floating Undefined behavior on digital read Value might stay or it might alternate quickly (50Hz hum) Input 5V SPST Solution: Connect to ground value via resistor Pull-Down Resistor 10K

42 Pull-Up Resistor Pull-Up resistor is equivalent Pulls voltage up to high logic state 5V 10K Input SPST

43 Interactivity 5V SPST 1K Output 12 Input 13 LED 10K D

44 /* * Switch and LED test program */ int ledpin = 12; // LED is connected to pin 12 int switchpin = 13; // switch is connected to pin 13 int val; // variable for reading the pin status void setup() { } pinmode(ledpin, OUTPUT); pinmode(switchpin, INPUT); // Set the LED pin as output // Set the switch pin as input void loop(){ val = digitalread(switchpin); // read input value and store it in val If (val == LOW) { } digitalwrite(ledpin, HIGH); // check if the button is pressed // turn LED on } if (val == HIGH) { digitalwrite(ledpin, LOW); } // check if the button is not pressed // turn LED off

45 Switch Debouncing Switches and Buttons are mechanical mechanisms Not truly binary! Many switches don t change instantaneously from on to off they bounce between states Especially momentary buttons, spring loaded buttons and tilt switches where a mass moves to make or break contact

46 Switch bounce

47 Naïve Debounce Read Input once => Wait for bounce duration => Read again Only if readings agree change state Issue? Introduces unnecessary latency Bounce duration needs to be evaluated empirically

48 Counter based Debounce unsigned char counter; //Variable used to count unsigned char T_valid; //Variable used as the minimum duration of a valid pulse void main(){ P1 = 255; // Initialize port 1 as input port T_valid = 100; //Arbitrary number from 0 to 255 where the pulse if validated while(1){ //infinite loop if (counter < 255){ //prevent the counter to roll back to 0 counter++; } if (P1_0 == 1){ counter = 0; //reset the counter back to 0 } if (counter > T_valid){ //... // Code to be executed when a valid pulse is detected. //... } } } //... //Rest of you program goes here. //

49 Analog solutions Introduce capacitor into circuit Capacitor resists the voltage change on the out pin Response speed and hence harshness of filter can be tuned exactly

50 15 Minute Break

51 Designing with Switches

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54 Key cap construction Conductive Layer Spacer Non Conductive Key Switch Membrane Conductive Layer

55 Key cap construction Conductive Layer Spacer Non Conductive Key Switch Membrane Conductive Layer

56 Keyboard Switch Matrix IBM compatible keyboard has 104(+) keys Issue? To expensive to read each key individually Depending on controller IO pins Needed for many different tasks Solution: Connect buttons in matrix fashion Keyboard: 16x8 matrix requires 24 pins

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58 Microcontroller Key Matrix Rows & Columns connected to microcontroller Controller drives circuitry and generates key events (key codes) Each row and column pin Can be used as in- or output pin Output pins are driven (low / high) Input pins are read (low / high) A C B D

59 Single Key Drive rows, read columns Drive columns, read rows A B C D E F G H I J K L M N O P

60 Multiple Keys Drive columns sequentially Read rows simultaneously A B C D E F G H I J K L M N O P

61 Multiple Keys - Ghosting and Masking Certain constellations may lead to erroneous key press/release events A B C D C is detected pressed or not Release of B can t be detected

62 Eliminating Ghosting and Masking Diodes restrict flow direction of current D

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65 Things that act like switches Many other devices (can) produce binary events just like buttons Proximity detector Touch sensor Light barrier

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68 Photo Diode IR Emitter

69 Forward / Backward rotation is ambiguous!

70 Quadrature Encoding Clockwise Rotation Phase A B C-Clockwise Rotation Phase A B

71 Example: Rotary Encoder

72 Continuous Input

73 Voltage divider Convert variable resistance to measurable signal Resistance-varying and fixed resistor in series, measure voltage between them V Out = V supply R 2 R 1 + R 2 No discrete event Polling required ADC necessary

74 Example: Potentiometer Resistive element Strip or arc Sliding contact (Wiper) Electrical terminals at each end of resistive element Electrical terminal at the wiper R

75 Further examples Force Sensing Resistor

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77 Further examples: Flex sensor Resistance straight: 10kΩ Resistance bent: 40kΩ

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80 Force sensing Switches Instead of measuring force directly measure velocity Delay between closing of two switches Time between break and make of SPDT switch Or two staggered switches

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82 Optical Mice Optoelectronic sensor essentially a super fast low-res camera Typically 18x18 pixel Sometimes >3000Hz (gaming mice) LED at grazing angle Onboard microprocessor computes 2D coordinates

83 Optical Flow Mouse sensor operates under very constraint circumstances Translation only Fixed illumination Simple flow methods are sufficient

84 Optical Flow Optical Flow estimates motion of Camera Objects Between two successive frames In the case of the mouse the problem is slightly easier: Moves in 2D On a flat surface Controlled Illumination Can be computed efficiently in hardware

85 Onboard Optical Flow Cross-Correlation Computes similarity between signals (offset in some dimension(s)) CC-based Optical Flow computation Shift frame t 0 relative to frame t 1 n times in all directions Highest correlation score signifies motion direction

86 Optical Flow in Hardware Implemented on ASIC Integrates imaging sensor and processor Compute optical flow via correlation Store previous frame (Row- and column-wise) sums of XORs of single pixels Integrate decisions to track movement Massive parallel implementation Very fast in hardware

87 Laser Optical Mice Uses infrared laser diode rather than LED for illumination. Exploit laser speckle Pattern produced by mutual interference of several wavefronts of the same wavelength but different phase and amplitudes Observable when coherent lightsource (i.e. laser) is shown onto a surface (each point on the surface acts as secondary lightsource) Increases observable structure in the environment Allows for much higher sensing fidelity and faster update rate Works on more surfaces (even glass)

88 Summary Overview of input devices built from simple buttons and switches Discrete (Game controller buttons, Keyboards) Analog(-ish) (Mouse-Wheel, Data Glove) Electronics basics Current, Voltage, Resistance, Power, Circuits Working principle of several fundamental input devices Mouse Keyboard

89 Application Cards You have been given three cards Write down three real-world application ideas using some of the technologies you learned about today A (traditional) input device that you are sure will work A non-traditional input device that re-purposes sensor technologies in a creative way (e.g., Bop-It, PhotoHelix) An out-there input device you don t even need to be sure whether it will work or not creativity counts most. You have 10 Minutes time Drop off your cards when you are done We will discuss a select number of your designs next week

90 Reading suggestions Scherz, Paul (2006). Practical Electronics for Inventors. McGraw-Hill Tucker, Allen B. (2004). Computer Science Handbook (Fundamental Input and Output Devices). Chapman and Hall. 2 nd Ed. Lyon, Richard F. (1981). The Optical Mouse and an Architectural Methodology for Smart Digital Sensors. Xerox PARC TechReport Borchers, Jan (2013). Arduino in a Nutshell