Bus & Signal Processing

Transcription

1 Prototyping Electronic Devices Class 12 Bus & Signal Processing Deqing Sun, Peiqi Su ITP, Fall, 2018

2 What is bus 2

3 Differences between Bus and Cab? 3

4 Differences between Bus and Cab Bus is capable to carry many passengers that sharing the same route. 4

5 In electronics How to connect different devices so that they can communicate with each other? Device A Device B Device A Device B Device C Device D Device C Device D Cab Concept Bus Concept 5

6 Bus in electronics Bus is a set of connections shared by multiple hardware components. Signals are dropped off or picked up at every device attached to the bus. What s the advantage to use bus? Cab Concept Bus Concept 6

7 Advantage of Bus The purpose of buses is to reduce connections between components. It carries out all communications over a single data channel. Cab Concept Bus Concept 7

8 Parallel bus and Serial bus Buses can be divided into two types: Parallel: Conveying multiple binary digits (bits), simultaneously Serial: Sending data one bit at a time, sequentially 8

9 Examples of serial and parallel interface Flag semaphore Parallel. Multiple bits at same time (two flags with various position) Morse code Serial. One bit at a time (either on or off) 9

10 Serial/Parallel Hard drives Hard drive buses shifted from Parallel (left) to Serial (right) since Serial bus has 2 main advantages Fewer wires (Very useful) Faster clock speed capability 10

11 Parallel Bus is rare today Due to the complexity in connection, parallel bus is rarely used today. Memory module is one of the few hardware still using parallel bus. As we won t use it, we won t talk much about it in this class. 11

12 Common serial buses in ITP projects Synchronous I2C - 2 wires SPI - 3 wires+1 slave select for each device (e.g. 4 wires for one device, 5 for 2) Asynchronous RS wires 1-Wire - 1 wire 12

13 Diff. between synchronous and asynchronous Whether the interface uses a clock line to synchronize signal. Asynchronous interface sends data at certain rate. Receiver needs to count time by itself. Synchronous interface has a clock line that inform receiver when to receive a new bit. What if sender freezes for a while? 13

14 USB 14

15 USB s advantage USB can supply some power USB is robust USB support hub USB is supported by a lot of devices 15

16 Extend USB Extend USB with repeater: This type of USB extension cord has a hub on it s female end. It decode signal and encode again to fix distortion in transmission. Limited Length, High reliability, High speed. 16

17 Extend USB Extend USB with ethernet cable: This pair of adaptor convert USB signal on Ethernet cable and back. You can use a long cable for connection. Longer Length, Lower reliability, Low speed. Arduino, thermal printer, etc OK Webcam, Kinect, Storage, etc, NOT OK 17

18 Lesson we learned from USB extension We used non-shield ethernet 30ft cable to extend USB from computer to control circuit. Everything works well until show starts. Frequent disconnections happens. Using shielded cable will be more reliable, especially in space filled with radio noise like trade shows. 18

19 I2C 19

20 What is I2C The Inter-integrated Circuit (I2C) Protocol is a protocol intended to allow multiple slave digital integrated circuits ( chips ) to communicate with one or more master chips. It uses 2 wires. Normally we only have one master and Microcontroller will take that role. It requires pull-up resistors. 20

21 Pull-up & Pull-up resistor When you use a button and connect the button between input Pin and GND, you need to add a resistor between input Pin and VCC, to pull input Pin level to VCC. Such resistor is called Pull-up resistor. 21

22 How I2C works Master sends out clock and address of a slave device. If there is a slave device with matching address, it will respond and all other slave devices will keep silent. Arduino's Wire Library handles all lower level work. 22

23 Address of slave device The Wire library uses 7 bit addresses. The addresses from 0 to 7 are not used because they are reserved. So, there are addresses are available =120 As long as slave devices have different address, there will be no conflict. 23

24 Address of slave device is not arbitrary When you get a I2C chip. Manufacturer usually already pre-programmed its slave address. Some chips may let you change the last few bits of its address, but you can not change all bits of it. If you are using a microcontroller as slave, you may change the whole address. 24

25 Figure out the slave address Let s say we like this LED matrix from adafruit. It has a controller called HT16K33. We open it s datasheet. 25

26 Address of HT16K33 The address is (binary) A2 A1 A0 And A2, A1, A0 is configurable. If one pin is unconnected, the corresponding bit will be zero. For example, If we only connect A1, The devices address will be =0x72 Quiz: if A0 and A2 are connected, the address? =0x75 26

27 Pads for address configuration These 3 pad are used for configuration. You can bridge them to change address. Quiz: How should we set address to 0x74 ( )? Bridge A2 pad only Quiz: In the same I2C bus, how many HT16K33 can I connect? 8 (000,001,010,011,100,101,110,111) 27

28 A common I2C device: EEPROM EDID EEPROM, describes monitor s parameters in VGA, DVI and HDMI SPD EEPROM, describes memory module s size, type and speed, etc. Simple IC card, used to keep non-critical simple data. Used in early laundry system, etc. 28

29 SPI 29

30 SPI connection SPI uses separate connections for sending and receiving data. Each slave has own slave select. SPI device doesn t have address. 30

31 Compare to I2C SPI has separate input and output lines. SPI don t need to send address. SPI is faster and used on BLE module and SD cards. Due to the complexity of wiring (at least 4 vs 2), SPI is not as common as I2C. 31

32 One Wire 32

33 1-Wire 1-Wire is an interesting bus that only use one wire. For low power application, even power wire can be removed by using data line to provide power. Each 1-wire device has been programmed with a unique ID. Master device can perform a search algorithm to find all available devices on bus. 33

34 1-wire devices Temperature sensor IO breakout ibutton Widely used as checkpoints in security guard tour system 34

35 RS485 35

36 Rs485 RS485 is a type serial communication, but it uses a pair of wires to send one signal. You can use a transceiver to translate serial on Arduino to and from RS

37 Why do we need RS485 RS485 use twisted wire pair to transmit data. If you do wiring in industrial standard level, RS485 can go up to 4000ft (1200m) 37

38 Where we should use RS485 If you need to send data in a long distance, RS485 is a good choice. In public theater, we used RS485 to transfer data from main controller to LED displays. 38

39 Quiz 39

40 Quiz: which bus to use? Scenario: The Penis Wall 4 x 4 feet; 81 modules; control each module individually 40

41 Quiz: which bus to use? Scenario: The Bay Lights 1.8 miles (2.9 km) of the cables; 25,000 individual white LEDs; control each LED individually 41

42 Quiz: which bus to use? A light bulb? For power transmission without communication. Bus is not needed. 42

43 in-class practice i2c 43

44 What will we do We will connect 2 Arduino with i2c. The master Arduino will send a value to slave Arduino to control the onboard LED, and read analog value on A0 from slave Arduino. 44

45 Connect 2 Arduino Connect 5V, GND, SCL and SDA ports. On Arduino Uno: SCL is on A5 SDA is on A4 Arduino_i2c_master.ino Arduino_i2c_slave.ino USB to computer 45

46 Code on Master Arduino Upload class12/arduino_i2c_master to Master Arduino github.com/deqingsun/prototyping-electronic-devi ces 46

47 Code on Slave Arduino Upload class12/arduino_i2c_slave to Slave Arduino github.com/deqingsun/prototyping-electronic-devi ces 47

48 What to observe After uploading code to slave Arduino, connect USB to master Arduino. Open Serial monitor. How the LED on slave blinks? How you change the blinking timing? Try to connect A0 of slave Arduino to 5V or GND. What you see? If you finish the experiment, how you connect 2 slave Arduino to one master one? 48

49 Signal Processing 49

50 Signal Processing Signal Processing - Averaging - Hysteresis - Peak detection - Envelope detection 50

51 Why we need signal processing? When getting signals from physical world, we get some noisy signal. For example, you read a sensor value or do computer vision and get location. You can do signal processing to clean signal or extract feature from signal. 51

52 When we need it FSR sensor: Noise affects ON/OFF triggering, we don t want false trigger caused by noise. 52

53 When we need it Pulse sensor: If we know position of each peak, we can calculate heart rate 53

54 When we need it Kinect: We want to know whether user waved his hand. The position of hand can be seen as an input signal. We know X,Y position of hand. What kind of change in hand position can be defined as waving? 54

55 Platform we use deqingsun.github.io/javascript-signal-processing/ Short link: bit.do/signalprocessing Open this link on phone Open this link on Laptop 55

56 UI explanation Graph of Values View of camera JS code playground 56

57 Camera view In camera view, it s looking for a magenta object in its view. You should see a green rectangle around your phone. Your phone s vertical position will be used as input, copied to global variable value_input 57

58 Graph of values global variable value_input is drawn in Red 255 global variable value_output is drawn in Blue Now Red and blue is overlapping. Value 0~255 0 Time 58

59 Code Playground This is the place you can write code to do signal processing. Code in this box will be executed every frame. After finishing coding, click Apply code. If there is no syntax error, your code will be applied to graph. Otherwise you will see the error message. Try to type: value_output=255-value_input; 59

60 Use a new variable In Javascript if we read a variable before we create it, we will get an error. if(typeof new_var === 'undefined'){ new_var=0; Create a variable and assign a new value }; Is this variable not created yet? 60

61 Algorithm 61

62 What if we need a smoother signal? We get a noisy signal, how to clean it? 62

63 Average Filtering 63

64 Average Let refresh what is averaging. We basically add a few values together and divide the sum with count of the values. 64

65 Average Filtering (smoothing) To smooth of a signal, we don t average all data points. We take each sample points and average them with a few values before it. The spikes are suppressed and the signal become much more smooth. 65

66 How to average a streaming signal We store N recent values and calculate their average. We can create a queue of certain length to store recent data points from stream. New data will be added and old data will be discarded. 66

67 Use ring buffer to keep data In real application, shift values in array may takes a long time. We can treat an array as ring buffer. New data will overwrite old data automatically. 67

68 Live demo Try this code in browser and play with it. 68

69 Code //average filtering if(typeof data_filter === 'undefined'){ //We need to initialize variable before we use them data_filter=[0,0,0,0,0,0,0,0]; }; if(typeof data_pointer === 'undefined'){ data_pointer=0; }; data_filter[data_pointer]=value_input; //store previous values into array data_pointer++; if (data_pointer==8) data_pointer=0; sum=0; for (i=0;i<8;i++){ //get average value from array sum+=data_filter[i]; } value_output=sum/8; 69

70 Trade off of queue length if(typeof data_filter === 'undefined'){ //We need to initialize variable before we use them data_filter=[0,0,0,0,0,0,0,0]; }; if (data_pointer==8) data_pointer=0; Too short: not enough to smooth noise (demo) Too long: desired signal will be smoothed (demo) You may want to do some experiment on how long queue you are going to use. 70

71 Try different queue length 5 Mins 71

72 What if we need a threshold on a noisy signal How we void jumping result caused by noise? 72

73 Hysteresis 73

74 Hysteresis in comparator When trying to convert a signal to boolean values, we may get unwanted transition due to noisy signal. 74

75 Live demo of a simple comparator Noise introduces glitches. //Direct Comparison if (value_input>(128)){ value_output=255; }else{ value_output=0; } 75

76 How to solve the problem Using 2 different threshold! 76

77 Live demo 77

78 Code to do threshold if(typeof value_was_above_threshold === 'undefined'){ if (value_input>value_threshold){ value_was_above_threshold=true; //We need to initialize variable before we use them }else{ value_was_above_threshold=false; value_was_above_threshold=false; }; } if (value_was_above_threshold){ if (value_was_above_threshold){ value_output=255; value_threshold=128-5; }else{ }else{ value_output=0; value_threshold=128+5; } } 78

79 Try bigger and smaller Hysteresis 5 Mins 79

80 We need heartrate from heartbeat signal How we know when is heartbeat? 80

81 Peak detection 81

82 Peak detection What is a peak: A point higher than previous value and next value. 82

83 Live demo 83

84 Code to do peak detection (Simple) if(typeof previous_frame_data === 'undefined'){ //We need to initialize variable before we use them previous_frame_data=0; }; if(typeof two_frame_ago_data === 'undefined'){ //We need to initialize variable before we use them two_frame_ago_data=0; }; if (value_input<previous_frame_data && two_frame_ago_data<previous_frame_data){ //the Y axis is pointing downward this this example value_output=255; }else{ value_output=0; } two_frame_ago_data=previous_frame_data; previous_frame_data=value_input; //push new data and discard old ones. 84

85 Try to modify code to valley detection 5 Mins 85

86 Improved Peak Detection You may miss some peaks if you just compare 3 points. A better way to do peak detection is to check if signal has changed its trend. 86

87 Improved Peak Detection When algorithm is looking for peak, it will record highest value since last valley point. Once current value is lower than highest value by delta, then we found a peak. Signal decreased from highest point by delta Then we look for valley in opposite way until we find it Looking for Peak Looking for Valley Signal increased from lowest point by delta 87

88 Adjust sensitivity of algorithm You can change delta to change sensitivity of the algorithm Delta = 3 A bigger delta will be more resistant to noise, at the cost of latency. Delta = 30 88

89 Try better peak detection Try the code and change delta. 5 Mins 89

90 Envelope detection 90

91 How we know a person is waving hand? 91

92 What is envelope Envelope function is a smooth curve outlining its extremes. 92

93 Hand movement and Envelope If you hand hold still and them move up and down, the difference of upper and lower envelope will increase. So you can use difference of upper and lower envelope to figure out if you hand is waving or still. Upper Envelope Lower Envelope 93

94 Envelope detection When we want to know the range of a changing signal we can detect it s envelop to determine it. We have a slowly decreasing value, but it will go up to signal value if it is smaller than signal 94

95 Live demo 95

96 Code to do Envelop detection //envelop detection lower if (value_input<value_output){ value_output=value_input; }else{ value_output+=0.5; } //envelop detection upper if (value_input>value_output2){ value_output2=value_input; }else{ value_output2-=0.5; } 96

97 Change decrease speed of envelope 5 Mins 97

98 Wrap Up

99 Next class We will discuss: Design a case for PCB Bluetooth low energy Please bring: A Computer with Chrome installed A ios device supports BLE and you can install app 99