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IAT267_Week 12.docx

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Simon Fraser University
Interactive Arts & Tech
IAT 267
Helmine Serban

Serial Communication Synchronous: 12C, SPI, Microwire Asynchronous: MIDI, Internet Communication Synchronous Serial Communication Uses two wires -data -clock (controls the rate at which data is sent) Devices -master device sends a timing pulse on the click wire every time it is ready to send or receive a bit of data shifting with each clock pulse you shift over the next bit of data Asynchronous Serial Communication Both devices have their own separate clock to keep track of time -the sender sends pulses representing the data being transmitted at an agreed-upon data rate -the receiver listens for pulses at that same rate Wireless Communication Advantages -no wires -simpler physical design for projects where devices have to move and talk to one another Examples -wearable sensor systems -digital musical systems -remote control vehicles Limitations of Wireless Communication Never as reliable as wired communication -less control over the sources of interference It is never just one to one communication -broadcasting of signals where everyone can hear -interference with other communication Wireless communication does not mean wireless power -mobile devices means battery power Electromagnetic radiation Types of Wireless Communication Infrared-needs line of sight Radio-omnidirectional (no light of sight needed) Transmitters-send a signal, cannot receive one Receivers-can receive a signal, cannot send one Transceivers-can both send and receive, more expensive For most application, it makes sense to use a transmitter-receiver pair Infrared Communication Works by pulsing an IR LED at a sent data rate Pulses are received using an IR photodiode Same as serial communication, only with infrared light There are many sources of IR light: sun, incandescent light bulbs, any heat sources It is necessary to differentiate the IR data signal from other IR energy-carrier wave Differentiating the IR Signal The receiver picks up all the IR light, but filters out anything that is not vibrating at the carrier frequency The carrier wave method allows transmitting data with no interference from other IR sources (unless they have the same frequency as the carrier wave) Data Protocols for IR Varies, depending on manufacturer To decode the signal, need to know the carrier frequency and the message structure Carrier typical frequency: 38-40 KHz Low data rate: -500-2000 bps This low speed is acceptable for remote control applications Do not use an 8 bit data format, 12, 15, 20 bit format is more common IR Detectors IR detectors are little microchips with a photocell that are tuned to listen to infrared light. They are almost always used for remote control detection-every TV and DVD player has one of these in front to listen for the IR signal from the clicker. Inside the remote control is a matching IR LED, which emits IR pulses to tell the TV to turn on, off, or change channels IR light is not visible to the human eye which means it takes a little more work to test a setup Characteristic of IR More limited than radio Cheaper Requires less power Remote control applications Arduino and IR Communication Control something connected to Arduino with a standard remote control Or inegrate Arduino into an existing infrared remote system -this is harder to do, as you have to look into the protocol and understand how it works -first step would be to indentify the protocol Radio Communication Relies on the electrical property called induction -any time you vary the electrical current in a wire, you generate a corresponding magnetic field -the changing magnatic field induces an electrical current in any other wires in the field -the frequency of the magnetic field is the same as the frequency of the current in the original wire Sending a Signal How radio works: -generates a changing current in one wire at a given frequency -at
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