1. ECE 101 An Introduction to Information Technology Digital Sensors

2. Unit Prefixes teraT10 12 gigaG10 9 megaM10 6 kilok10 3 decid10 -1 centic10 -2 millim10 -3 micro  10 -6 nanon10 -9 picop10 -12

3. Information Path Information Display Information Processor & Transmitter Information Receiver and Processor Source of Information Digital Sensor Transmission Medium

4. 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

5. Electric Circuit Laws Multiple loads –Series – same current –Parallel – same voltage Resistance and Ohm’s law, v R =i R R Kirchhoff’s Laws –Voltage law: v 1 + v 2 + v 3 + …. = 0 (sum of voltages around a loop is zero) –Current law: i 1 + i 2 + i 3 + …. = 0 (sum of currents at a node is zero)

6. 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

10. 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: N W = N C + N R –Number of switches, N S = N C * N R

12. 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

13. 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)

14. 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!

16. Infrared (IR) Range Sensors

17. Uses variation of proximity sensor to determine the range of an object for setting the focus of an auto focus camera S R f x receiver transmitter R/S = f/x S and f fixed by camera design

18. Digital IR Range Sensors

19. Uses an array of small detector elements - no determinations or calculations needed S R f receiver transmitter R/S = f/x S and f fixed by camera design

20. Inverse Square Law Key law in physics, gravity, light intensity, Coulomb’s law in E&M… I=P/A where A=  r 2, or I~1/ r 2 –Determines the spacing of antennas in cellular telephone system –Can be used to locate a transmitting signal

22. Inverse Square Law r = r o R = R o I (r =  r o ) = P/(  2 r 2 ) = I (r = r o ) /  2 r =  r o R =  R o