Systems & Devices Part 1

Transcription

1 Systems & Devices Part 1 Alexander Nelson February 5th, 2018 University of Arkansas - Department of Computer Science and Computer Engineering

2 What composes wearable, ubiquitous, or invisible systems? 0

3 Components of Systems Ubicomp systems are composed of a subset of the following: Sensors Actuators Communications Displays Storage Computation where the components & scale of each is defined by the application 1

4 Sensors

5 Types of Sensors Many different types of sensors Wikipedia categorization (summarized): Acoustic Chemical Electric Current Environmental Proximity Inertial Optical Pressure Force Thermal 2

6 Sensor Interfaces Systems use many interfaces to obtain sensor values These include: Binary Signals Analog to Digital Parallel Interfaces Serial Interfaces (SPI, I2C, UART) Pulse Width Modulation 3

7 Binary Signals Binary Signals 0 or 1 Pushbuttons, Threshold values, counts, etc... P2 is latched periodically Will be 0 unless switch is engaged 4

8 Debouncing Imperfect contact can create glitches Use delays to verify signal is steady 5

9 Analog vs. Digital Analog Digital 6

10 Conversion To work with sensor data, analog signals must be converted to digital Analog to Digital Conversion (A to D) 7

11 Sampling/Conversion Sampling Converting Analog to Digital Values Precision/Quantization Errors Error introduced because digital values have a defined precision Aliasing Errors Error introduced by periodic signals Nyquist Rate Minimum rate at which periodic signal can be sampled without introducing aliasing errors 8

12 Aliasing Error Aquisition-and-IO/The-Fine-Art-of-Analog-Signal-Sampling.aspx 9

13 Measurement Circuits Sensor manufacturers create elements that have a predictable response to a stimulus These responses modulate a quantity that can be sampled by a digital system Typical quantities: Resistance Capacitance Inductance 10

14 Analog to Digital Voltage Divider Resistor Sensors Thermometers, Photoresistors, Force sensors, etc... Measure resistance through two known quantities Derived from Ohm s Law (w/ assumptions) 11

15 Analog to Digital Wheatstone Bridge Wheatstone Bridge Voltage Measurement Can allow differential measurement, non absolute references, and can be extremely precise 12

16 Analog to Digital Capacitance Measurement 13

17 Analog to Digital Capacitance Measurement Capacitance can be measured by the voltage change over time 14

18 Parallel Interfaces Parallel Interface Many binary signals to represent word-length values D0-D7 represent a single byte to be transferred 15

19 Serial Interfaces Series a number of things coming one after another Serial Interface Bits transferred one after another 16

20 Serial Interfaces UART UART Universal Asynchronous Receiver-Transmitter Asynchronous No shared clock Data transfer is unidirectional Transmission Speed Usually given in baud (bits per second) Receiver & transmitter have foreknowledge of transmission speed Data frame Data transferred byte-by-byte Each frame is bordered by start & stop bit(s) 17

21 Serial Interfaces SPI SPI Serial Peripheral Interface Synchronous unidirectional master slave data transfer Master device configures clock, clock polarity, and when communication occurs Data frame Frame started by a logic 0 on the Source Select line Determines which slave device is to listen Data is transferred bit-by-bit, latched at either rising or falling edges 18

22 Serial Interfaces SPI 2 SPI Timing Diagram 2 Peripheral Interface Bus#/media/File:SPI timing diagram2.svg 19

23 Serial Interfaces I2C I2C Inter-Integrated Circuit (I-squared-C) Address-based 2-wire communication interface 20

24 Serial Interfaces I2C Data Transfer 1. Data transfer initiated(s) SDA pulled low, SCL stays high. 2. SCL is pulled low, and SDA sets the first data bit level while keeping SCL low (during blue bar time). 3. The data are sampled (received) when SCL rises for the first bit (B1). For a bit to be valid, SDA must not change between a rising edge of SCL and the subsequent falling edge. 4. This process repeats, SDA transitioning while SCL is low, and the data being read while SCL is high (B2,...Bn). 5. The final bit is followed by a clock pulse, during which SDA is pulled low in preparation for the stop bit. 6. Stop bit (P) signaled when SCL rises, followed by SDA rising 21

25 Serial Interfaces I2C Addresses I2C has only 2 data lines Uses addresses to specify which chip listens Address is 7 bits followed by a write bit Write bit specifies if action is to read or write at register address 22

26 Pulse Width Modulation Pulse Width Modulation Encoding message through pulsing signal 3 3 By Zureks - Own work, CC BY-SA 3.0, 23

27 Pulse Width Modulation Applications of PWM: Sensor output Servo Input LED dimming Power Delivery 24