Lecture 7: Signal Processing V EEN 112: Introduction to Electrical and Computer Engineering Professor Eric Rozier, 2/27/13

SCHEDULE

Schedule DateMW 3/4Wrap up signalsNASA Guest Speaker 3/11Spring Break 3/18Computer Engineering 3/25Computer EngineeringMidterm II 4/1EE/Circuits 4/8EE/Circuits 4/15EE/Circuits 4/22Course Synthesis

No Lab this Week Happy early Spring Break

CAPTURING SIGNALS

What we’ve done so far… Talked about… – Why signals are important – How to sample signals – How to quantize signals – How to store signals in computers What about how to collect or capture signals?

First a bit about Electricity We talked a bit about voltage so far, but what is it really?

Electricity The flow of electrons in a conductive material. Typically we represent the flow of “holes” rather than electrons. – This is due to historical reasons, more on this in other classes.

Voltage and Current The most basic ways in which we discuss the flow of electrical charge is voltage and current. We will describe these and other EE terms both as the flow of electrical charge, and using the “hydraulic analogy”

Voltage Voltage is the potential difference in electrical charge between two points in a circuit. – Measured in Volts In the Hydraulic analogy, we envision this as water pressure.

Current Flow of electrons in a circuit. – Measured in Amperes or Amps Hydraulic analogy, volume of flow of water through a pipe.

Resistance All wires resist the flow of electrical charge, just as all pipes resist the flow of water I – Current V – Voltage R - Resistance

Resistance What happens if you were to keep pressure constant, but pinch the pipe closed?

Resistance What happens if you were to keep the flow constant, but pinch the pipe closed?

Signals to Voltage Signals are some physical phenomenon – How do we get from signal to voltage?

A quick note… A lot of what we will talk about today you won’t understand 100% Being an Electrical and Computer Engineer means learning a lot of specialized (but useful!) information – It takes time

EEN

ECN

EAN

ESN

The purpose… Not to scare you… To show you there are answers, which you will learn in time.

SENSORS

Microphones

Condenser Microphone

The capacitance (C) is inversely proportional to the distance between parallel plates. Sound levels compress the plates.

Piezoelectric Microphone Some materials produce a voltage when subject to pressure. – We call this effect Piezoelectricity Carbon microphones are similar – Change resistance in response to changing pressure

Image Sensors CCD – Charge Coupled Device Photons striking the plates add electrons to wells.

Image Sensors Wells can be “read” by applying positive charge to plates, and shifting the electrons towards a circuit.

Image Sensors CMOS – Complementary metal-oxide semiconductor – Active pixel sensor – Light sensor coupled with a signal amplifier circuit.

Image Sensors A Bayer Mask allows only certain wavelengths of light to strike each plate.

Bayer Mask

Touch Screens

Infra-red Touch Screens

Resistive Touch Screen

Capacitive Touch Screen

Magnetometers A very common type is the Hall Effect magnetometer. Charge particles (electrons, 1) flow through a conductor (2) serving as a Hall sensor. Magnets (3) induce a magnetic field (4) that causes the charged particles to accumulate on one side of the Hall sensor, inducing a measurable voltage difference from top to bottom. Edwin Hall discovered this effect in 1879.

Accelerometers Uses: Navigation Orientation Drop detection Image stabilization Airbag systems The most common design measures the distance between a plate fixed to the platform and one attached by a spring and damper. The measurement is typically done by measuring capacitance.

Gyroscopes Optical gyros: Leverage the Sagnac effect, where a laser light is sent around a loop in opposite directions and the interference is measured. When the loop is rotating, the distance the light travels in one direction is smaller than the distance in the other. This shows up as a change in the interference.

Antennas

Electro-Magnetism It turns out magnetism and electricity are related…

Antennas Antennas couple electric connections with electromagnetic fields Radio waves are just electromagnetic waves which propagate through the air

Antennas

Electromagnetic fields induce current oscillations in the electrons present in an antenna. Hydraulic Analogy – Water wheel

Spedometer

Fuel Gauge

Switches and Dials

Potentiometers

Buttons and Switches