1 / 23

Interface Design

Interface Design. Omid Fatemi. Interfaces and Interfacing. Definitions of “interface” from Webster’s Dictionary:. noun: the place at which independent systems meet. and act or communicate with each other. e.g. human - machine interface. digital - analogue interface.

bob
Télécharger la présentation

Interface Design

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Interface Design Omid Fatemi

  2. Interfaces and Interfacing Definitions of “interface” from Webster’s Dictionary: noun: the place at which independent systems meet and act or communicate with each other. e.g. human - machine interface digital - analogue interface terminal - network interface TTL - CMOS interface parallel or serial interface verb 1: to connect by means of an interface. verb 2: to become interfaced. verb 3: to interact or co-ordinate harmoniously. e.g. to interface a printer to a computer to interface a PC to a mainframe to interface TTL logic with ECL logic

  3. 1) The human - machine interface determines the ultimate success or failure of many computer- based systems. 2) Digital systems exist within and must successfully interact with an analogue natural environment. Digital - analogue interfaces are unavoidable. 3) Rather than designing digital systems from elementary components, computer engineers more typically assemble new systems from existing subsystems. Interfaces between digital hardware subsystems and between software modules must be thoroughly considered. Why is computer interfacing important ?

  4. Why is computer interfacing important ? 4) With advances in technology, special attention must increasingly be paid to analogue effects affecting high-speed “analogue” interfaces. 5) Interfaces are a key area of standardization activity. The choice of standards can have great competitive implications. 6) Interfacing software is typically tricky and time-consuming to design and test. Much effort can be saved if proper interfacing techniques are adopted (and poor interfacing techniques avoided) and good design practices and design strategies.

  5. Human-machine interface: Input devices: keyboard, mouse, microphone, camera Output devices: CRT, printer, light panel, audio amp. Digital - Analogue Interface: Input devices: A/D converters, modems, sensors Output devices: D/A converters, modems, transducers, actuators, stepper motors Control devices: switches, multiplexers, amplifiers, attenuators Digital - Digital Interface: Connectors: wires, ribbon cable, coax, twisted pair, PCB I/O devices: buffers, level-shifters, synchronizers System-Level Interfaces Human Users Analogue Environment Digital- Human- Machine Analogue Interface Interface Digital-Digital Interface Other Digital Systems

  6. An Example – PC Computer Serial Port Controller Lab Board Keyboard CPU Cache Mouse Memory Controller Main Memory Parallel Port Controller Printer Hard Drive Disc Controller Diskette Drive Diskette Controller Video Controller CRT System Bus

  7. Typical Mechanisms at Interfaces 1) Data buffering and flow control -- helps compensate for short-term mismatches in data generation and consumption rates -- groups data into larger, more efficient chunks 2) Synchronization, handshaking -- compensates for asynchronous clocks, clock skew affecting synchronous signals, devices with different response times -- bit stuffing to equalize bit rates (telecom technique) 3) Digital processing -- framing, packet assembly and disassembly -- data communication protocols -- encoding, decoding, code conversion -- error detection and error correction -- data compression (e.g. using Huffman codes) 4) Analogue signal conversion and conditioning -- restore correct voltage and current levels -- restore correct signal rise and fall times -- pulse-shaping and channel equalization -- take precautions to reduce noise and reflections -- carrier modulation and demodulation

  8. Compute Convey Cooperate Typical Interface Design Connect Sense Reality Touch Reality Connect Transform Embedded Systems Micros Assembler, C Real-Time Memory Peripherals Timers DMA Busses Protocols Standards PCI IEEE488 SCSI USB & FireWire CAN PC interfaces HCI

  9. Sensors more generally a transducer: “a device that converts variations of one quantity into those of another”

  10. Sensors for Box Counting • Sensors connect the digital world to the analog real world • light sensistive resistivity • voltage divider for change in resistance • data logged by a computer

  11. Shaft Angle With Potentiometer • shaft angle proportional to voltage Vs • voltage Vs changes because of the change in resistance • simple application of Ohm’s law • current is constant

  12. Linear Variable Displacement Transformer (LVDT) • moving iron core changes properties of transformer • iron core position changes primary/secondary voltage ratio • difference in phase is measured and tranformed to a voltage

  13. Strain Guage • resistance varies with the ammount of stretching (strain) • flexure can be measured with a strain guage • force can also be measured

  14. Thermocouple • Seebeck effect: current will flow through a junction of disimilar metals if there is a temperature difference • millivolts and non linear • varies from 6 uV/C to 90 uV/C

  15. Thermopile • multiple thermocouples can be connected together to create a thermopile where multiple measurements can be used to find the arithmetic mean of several temperatures

  16. Phototransistor • current through external resistor varies with light intensity • can be used to detect light levels or movement • sensitive to different colors or wavelengths of light

  17. Hall Sensor • material of thickness t has current i flowing through it • magnetic field H perpendicular to i • voltage developed on third axis • E = RHi/t • R is hall constant

  18. Sensor Resolution Improvement

  19. Nonlinear Characteristics • Hysteresis is caused by memory • Saturation is when sensor input exceeds range • Breakdown is usually a damaged overdriven sensor • Bang-bang is a sudden large change in output • Dead zone is where input change makes no difference

  20. 2 Dimensional Accelerometer • ADXL202: Low-Cost ($25) 2g Dual Axis Accelerometer with Digital Output • dynamic acceleration (e.g. vibration) • static acceleration (e.g. gravity) • Low Power < 0.6 mA

  21. Ultrasonic

  22. Sensor Interfaces: summary • voltage source • directly measured • variable resistance • can be converted to a voltage and measured • voltage divider for coarser measurements • wheatstone bridge for finer measurements • variable capacitance • variable inductance • variable signal

More Related