How to Build a Digital Physical System - Lab Lecture 2

Today's Topics Electricity/Water analogy Electrical/Electronic circuit elements Basic formulae Useful conventions Reading and drawing schematics Using datasheets Test Equipment Practical – Wire stripping and Soldering

Water Analogy The following entities between a water circulation system and an electric circuit correspond fairly well Pressure – Voltage Water flow – Current Gate valve, Constriction – Resistance Valve – Switch One way valve – Diode etc...

Comparisons

Circuit Elements Power supply Resistors Capacitors Inductors Semiconductors

Circuit Elements Power supply  Energy source  Unit - Volts

Circuit Elements Resistor, Capacitors and Inductors  Passive components

Resistors Control current, dissipate energy as heat Unit – Ohms Symbol

Resistor Color Code Black Bears Raid Our Yellow Grain, Blue Violets Grow Wild

Capacitors and Inductors Energy storage elements Used in filters

Filters

Circuit Elements Semiconductors  Active devices  Transistors, ICs, LEDs, gates, diodes

Diodes Allow current flow in one direction only Rectification – change AC to DC

LEDs Diodes that produce light

Transistors Amplification, switching

Circuit Elements Subgroup of ICs  Microcontrollers (pic, Atmega etc.) Microcontroller development boards  Arduino

Types of Circuits Analog  Continuous values of voltage between Ground and Power Digital  Only On or Off, High or Low, or Ground or Power Hybrid

Datasheets Your crucial companion Consult the manufacturer's datasheet if unsure of a device's specific behaviour Of special interest  Pinouts  Absolute maximum ratings  Typical application circuit

Important sections

Typical Circuit

Pinouts

Features

Examples Analog  Most sensors, the physical world Digital  Your computer, most modern devices, your iPod for the most part

Schematics Symbolic representation of a circuit

Schematic More complex circuit

Useful Conventions Make your schematics and breadboards easier to understand and troubleshoot for yourself and others Learn to work like the pros

Conventions Wiring colors on breadboards Red for power Black for ground Others as needed, for example, inputs yellow outputs green etc. Schematic layout Maintain left to right signal flow Inputs on the left, outputs on the right(device & page) Power to top of page, ground to bottom

Some Common Formulas Ohm's law  E = V = IR Formula wheel  E - (emf) same as Voltage  R – resistance  I – current  P - power

Circuits and Ohm's Law For resistive circuits

Series and Parallel Circuits

Series circuit Same current, voltage divides Parallel circuit Same voltage, current divides

Using Ohm's Law Equivalent resistance = 1470ohms

Illustration on Board

Series Example

Parallel Example

Our First Circuit Using an LED Determine the resistor value Use a switch to activate the circuit

Components Battery(power supply) Resistor LED Switch

Functions Battery to power circuit LED to produce the light Resistor to control circuit current suitable for the LED Switch to turn the circuit 'on'

Draw Schematic

Determine Values LED rated for 11mA(milliampere) forward current at 2V (volts) For a 5V battery power and 2V across the LED the remaining 3V need to appear across the resistor Since LED is rated at 11mA(0.011A) and is in series with resistor, same current flows through resistor. So resistor value should be 3/0.011 = 272.7ohm. We will use 270 ohm.

Calculation on Board

Physical Setup and Demo

Power Calculation

Test Equipment Multimeter Oscilloscope Signal Generator Power Supply Logic Analyzer Hand tools

Multimeter Use to measure Voltage, Current and Resistance  Some measure frequency, capacitance, temperature and more *** Caution***  Take extra care when measuring current  Start with a selection higher than the highest expected value

Making Connections Voltage is measured across device in circuit Current is measured in-line in circuit Resistance is measured across device, outside circuit

Oscilloscope Provides detailed graphic representation of signals Essential for signals with ac components Usefull for monitoring noise

Wire Stripping and Soldering For connectivity on PCBs For connectivity with connectors For connectivity with panel components For connectivity with general parts

Wire Strippers Automatic Manual

Manual Strippers Use the wire size label on tool or.. Use a position with a hole slightly larger than the wire diameter

Manual Strippers Determine strip length Place wire on hole Grab firmly Strip

Soldering Tips for good soldering Keep tip clean Heat the parts, not the solder Do not move parts during cool down Keep tip temperature only as high as necessary Work with a damp sponge ready

Soldering is easy! Follow 3 simple rules Save yourself countless wasted hours in troubleshooting your project

Very Important ***Clean Tip*** ***Clean parts*** Hot enough tip for the job Larger parts need higher temperature 750 ~ 900 deg, normal 850deg ***remember to lower dial to 400deg when idling

Parts Safety Semiconductors, some capacitors are sensitive to heat Use heat sinks when necessary

Homework Simple series parallel circuit Simple LED circuit Simple light bulb circuit - (optional) Build 2 nd circuit, get details on wiki Short paragraph about what you wish to be able to do at the end of the 8 week session

Homework