Transcript Lecture 2
ECE 101 An Introduction to Information Technology Digital Sensors Unit Prefixes tera giga mega kilo deci centi milli micro nano pico T G M k d c m n p 1012 109 106 103 10-1 10-2 10-3 10-6 10-9 10-12 Information Path Source of Information Information Display Digital Sensor Information Processor & Transmitter Transmission Medium Information Receiver and Processor Electric Circuit Concepts • Charge, Q or q • Current, I or i – motion of charge (“through”) – Direct current – Alternating current • Voltage or electric potential, V or v (“across”) – Motion of charge occurs due to a force pushing on it – Work per unit charge is voltage – If current through an element results in an expenditure of energy, than a voltage or potential drop occurs – Battery • Power, P = V*I, or p=v*i Electric Circuit Laws • Multiple loads – Series – same current – Parallel – same voltage • Resistance and Ohm’s law, vR=iRR • Kirchhoff’s Laws – Voltage law: v1 + v2 + v3 + …. = 0 (sum of voltages around a loop is zero) – Current law: i1 + i2 + i3 + …. = 0 (sum of currents at a node is zero) Mechanical Switches • Break the flow of electrical current • May be activated by the outside environment, such as, change in switch position, temperature, acceleration • May be activated in series – open: no alarm – closed: alarm activated • May be activated in parallel – open: alarm activated – closed: no alarm Mechanical Switches • Note the matrix arrangement for the keyboard and the clever scheme to minimize the number of wires – Each key is a switch – Reduce the number of wires by using a matrix of switches formed by rows and columns of keys – Number of wires = number of columns + number of rows: NW = NC+ NR – Number of switches, NS = NC* NR Sensors or Transducers • Front end of information (electrical) systems • Converts physical energy into an electrical signal • Produce the data to be transmitted, processed and/or stored • Analog (continuous) or digital (example, a binary switch) • Mechanical, optical, thermal, electrical Optical sensors • Visible [UPC (universal product code) using lasers)], IR (remote controls) • Beam interrupt – presence of light may actuate a switch (often mechanical) • Digital Data transmission – use of threshold – Noise and weather (attenuation) not as significant – Beam intensity not a factor (good for cellular telephone) Optical Proximity Sensors • Unlike beam interrupt, the the transmitter and receiver in the same device. • Reading of Bar Codes, facsimile machines • Note the clever way of reading the UPC code at an angle and the operation of an auto-focus camera. Trigonometry is key here! Infrared (IR) Range Sensors Infrared (IR) Range Sensors • Uses variation of proximity sensor to determine the range of an object for setting the focus of an auto focus camera transmitter R S x R/S = f/x f receiver S and f fixed by camera design Digital IR Range Sensors Digital IR Range Sensors • Uses an array of small detector elements no determinations or calculations needed transmitter R S R/S = f/x f receiver S and f fixed by camera design Inverse Square Law • Key law in physics, gravity, light intensity, Coulomb’s law in E&M… • I=P/A where A=r2, or I~1/ r2 – Determines the spacing of antennas in cellular telephone system – Can be used to locate a transmitting signal Inverse Square Law R = Ro R = Ro r = ro r = ro I (r = ro) = P/(2r2) = I (r = ro) /2