Presentation on theme: "Electronics Merit Badge"— Presentation transcript:
1Electronics Merit Badge Old Colony CouncilMerit Badge UniversityMarch 2012Joe MulcaheyLen BarrettSean MulcaheyMention optional kit=$10 (same or equivalent required to complete badge)Homework: read MB pamphlet, bring in questionsRev. S, 01MAR12Based on the Electronics Merit Badge classes taught at the 2005 & 2010 National Jamborees
2Electronics Merit Badge Class Outline Class 1 Safety (Requirement 1)March 3 Electricity & Electronics IntroductionCircuit Diagrams & Schematics (2)Solving Circuit Problems using Ohm’s Law (5a)Class 2 Job Opportunities in Electronics (6)March 10 Test Equipment Demos (5b)Class 3 Proper Soldering Techniques (3)March 24 Kit Assembly (4)
3Safety with Electricity and Electronics Does this look safe to you? Rightmost picture looks to be from Korea. What does that say about electricity safety in the US and other places?
4Electricity SafetyHigh Voltage ( 120V AC or greater) – Safety mainly about not touching the wrong thingCurrent kills – Only 16 volts can kill when enough electrons flow through the heart or headVentricular fibrillation – Electrons passing through the heart causes muscles to seize, leading to deathIf the shock doesn’t kill you, you can still be badly burned from touching the wrong thingShock can be avoided by being educated about potentially dangerous situations. Stay away from them!!!
5How to Avoid Shock Turn power off before working on equipment Don’t touch circuits that could have high voltage on themDo not allow electrons to flow through the heart. I don’t think the snake knew about this detailThe snake crawled under the fence. Once through the fence, it felt the shock from the electric fence, and turned to bite the fence.This passed current through either its brain or heart, and that was it.Its body made a connection from the fence to ground, and was being shocked.The snake felt the shock and responded by striking at the source of its pain… the fence.My guess is that once it bit the fence, it provided a better electrical path from the fence, though its heart, to ground.
6Electronics SafetyElectronics generally uses lower voltages (less than 48 volts)You are usually working with DC voltage instead of AC voltageYou are usually more concerned with sparks from connecting the wrong wires together, or burning yourself with a soldering iron, or some similar eventEven when working with lower voltages, you may still receive an electrical shock from equipment you are usingEmphasis here is that electronics is inherently safer than electricity, because the voltages are much smaller. This does not diminish the necessity for safety.
7Personal SafetyBe aware of what you are doing, and where you are placing equipment and yourselfPay attention to hot soldering ironsKeep a good distance between you and those next to youKnow when you are working with high current and/or high voltage circuitsTHINK before you do somethingWear safety glasses when soldering
8One Hand RulePrevents current from flowing in one arm, through your heart, and out the other armKeep one hand in your pocket!
9Introduction to Electronics Electrical and Electronics Engineering are both career fields that are involved with Electronics TechnologyElectrical engineers specializing in power work with motors and generators, and design transmission lines and power plantsEEs specializing in electronics deal with communications, such as radio, television and telephony, radar and digital & analog circuit technologiesAll engineers draw from the fundamentals of science and mathematicsThey design and work with electrical, electronic, electro-optical, and electromechanical devices, circuits, and systems
10Introduction (Continued) Electrical Engineers collaborate with other professionals in developing sophisticated software tools that support design, verification, and testingElectrical engineering is a discipline that integrates many other disciplines, such as physics, chemistry, mathematics, computer software and hardware, solid-state electronics, communications, electromagnetics and optics, signals and signal processing, systems science, reliability, engineering economics, and manufacturingIn order to Learn about Electronics, we must first start by gaining an understanding of what electricity is, both AC (Alternating Current) and DC (Direct Current)
11Types of Electricity Static Electricity Static electricity is usually created when materials are pulled apart or rubbed together, causing positive (+) charges to collect on one material and negative (−) charges on the other surface. Sparks may result!How to generate static electricity? Every strand of hair is repelling the next strand of hair, as they all have the same electrical charge.Run comb through hair. The comb will attract paper.Walk across a carpet and touch a doorknob.Lightning occurs when a large enough charge accumulates between the bottom of a cloud and the earth, such that an ionization path is created between the two, and electrons flow…Examples of static electricity:LightningCombing hairWalking across carpet and getting shockedPulling out scotch tape
12Types of Electricity Alternating Current (AC) The common form of electricity from power plant to home/office. Its direction is reversed 60 times per second in the U.S.; 50 times in Europe.AC power is present in the home.Pay attention to safety around AC power.One idea to illustrate AC power is to get a scout to walk in one direction and then turn around and walk in the other direction. Each time he passes the instructor, he reaches out with his hand and pushes on the instructors hand. Though current flows in 2 directions, it is reasonably easy to see how it can be used to do electrical work.Examples of AC usage:Kitchens: Stoves, ovens, mixer, etc.Computers (the plug)Lights in houseHome air conditioners
13Types of Electricity Direct Current (DC) Type of electricity used in most electronics we have today. Current only flows in one direction (not both directions, like AC).We are talking batteries. Through a chemical reaction, batteries provide a flow of electrons --- current flow.Examples of DC usage:MP3 playersRadiosElectricity in carsAnywhere you use a battery for power
14Basics of Electronics Current: Defined as “flow of electrons” We will use positive flow, not electron flow when we talk about current.Current: Units of current is the AMPCurrent: Electrical symbol for current is I
15Current Flow – Water Analogy Water flows in the hose, entering at the top and exiting the bottomThe water is the “current”; the flow of electronsThe more water flowing in the pipe, the more electrons are flowing in the wireDifferent pipe diameters illustrates different resistance to water flow, which correlates to different resistor valuesGet 1 scout to walk across the room. Now, get 2 scouts to walk across the room.The scout is an electron, and by walking, is equal to current flow. Two scouts walking are two electrons, and are doubling current flow. I know this is hokey, but can be used when it makes sense during the class.
16Current Current: Defined as “flow of electrons” Current: Units of current is the AMPCurrent: Electrical symbol for current is ICommon units for current are:ampsmilliamps (mA): 1 mA = ampmicroamps (mA) : 1 mA = amp, or mAnanoamps (nA) : 1 nA = amp, mA, or mAIt is important that emphasis be placed on units. Ma = milliamp = .001 amp. It is necessary to get this correct, as it will be used when we do the calculations later.
17Voltage – Water Analogy Small height = low voltageBig height = high voltageheightThis is a very important concept to get across. Voltage, current and resistance are the basis for this class.heightGravity provides the force for water (current) to flowThis illustrates a small voltage, so electron flow is smallGravity provides the force for water (current) to flowThis illustrates a larger voltage, so electron flow is larger
18Voltage Volts is the electrical force that causes electrons (current) to flowUnits of volts is the VOLTThe symbol of volts is E or V. We will use VCommon units for voltage are:voltsMillivolt (mv) : voltMicrovolt (mv) : volt, or mVNanovolt (nv) : volt, mV, or mV
19Resistance – Water Analogy 10000ΩDifferent pipe diameters represents different resistor valuesThe smaller the diameter of the pipe, the larger the resistance1000Ω100Ω10Ω1Ω
20ResistanceResistance is an electrical property of a material that “resists” the flow of electronsThe schematic symbol for a resistor is:Common units for resistance are:ohmskiloohm: 1KΩ = 1000 ohms, 10KΩ = 10,000 ohmsmegaohm: 1MΩ = 1,000,000 ohmsThe units symbol for ohms is: Ω (ohms)Units are important in engineering. These are very common terms that are used all the time when talking about these components.
21Power – Water AnalogyIn electronics, power is equal to current X voltageThe units for power is the WATTThe symbol for power is W or PIn our water analogy, power isequal to water flow X pressureYou can see from the picture that more water flow will mean more force, and more pressure will mean more force
22Ohm’s Law One of the most important laws in electronics/electricity V = I x R : Voltage = Current x ResistanceVoltage is measure in volts, current is measured in amps, and resistance is measured in ohms1 amp, going through 1 ohm of resistance, results in a voltage drop of 1 volt1 V = 1 A x 1 ΩOhms’s law is the purpose of this class. Clear understanding of current and voltage and resistance is key in making ohm’s law comprehensible.
23More Ohm’s Law Different forms of Ohm’s Law: V = I x R : Voltage = Current X ResistanceI = V / R : Current = Voltage / ResistanceR = V / I : Resistance = Voltage / CurrentMake sure everyone understands this page. Make sure they understand that the units (decimal place) is extremely important when doing these calculations.Getting them to think about the alternative questions (1V and 1000V) is good – especially if they can understand the difference in current just by looking at the difference in voltage, (resistor is unchanged).Perhaps looking at the example, and asking about what the current would be if only the resistor was changed from 1000 ohms to 1 ohm, shows another way to look at this simple relationship.Volts = 10Resistance = 1000ΩCompute current:I = V / RI = 10 / 1000 = .01A.01A = 10mAQuestion: what would the current be if the voltage was 1 V? How about 1000 V?+10V1000 Ω
24Ohm’s Law Pie ChartIf you know any two values, you can get the other two with these formulas
25Bonus Ohm’s Law Question: Resistor Cube Resistances in series add: RTotal=2RResistance between points A and B = 5/6 OhmsWould take the typical second-year EE student about 8 pages of work to solve.Resistances in parallel divide: RTotal=R/2What is the resistance between points A and B?
26Where Did the Names of the Electrical Parameters Come From? Volts: Count Alessandro Volta ( ), Italian ScientistOhms: Georg Simon Ohm ( ), German PhysicistAmps: André-Marie Ampère ( ), French PhysicistWatts: James Watt ( ), British EngineerFarads: Michael Faraday ( ), British PhysicistHenrys: Joseph Henry ( ), American PhysicistOther Units:Coulomb, Gauss, Joule, Tesla and of course Smoot
27Smoot? What’s A Smoot?Smoot: A humorous unit of distance invented in 1958 by a fraternity at the Massachusetts Institute of Technology. The fraternity pledges of Lambda Chi Alpha measured the length of Harvard Bridge using pledge Oliver R. Smoot ('62). According to Smoot himself, the bridge turned out to be smoots long "plus epsilon," but this has been recorded as smoots "plus an ear." The bridge is still marked in smoots. Proposals to change the definition of the unit by remeasuring it with Smoot's son Steve (MIT '89) or daughter Sherry ('99) were rebuffed. One smoot equals 67 inches ( centimeters). Oliver Smoot became an attorney but continued his interest in standards and measurement. He is a past Chairman of the Board of Directors of the American National Standards Institute (ANSI) and past President of the International Organization for Standardization (ISO).I walked across this bridge thousands of times.
29CIRCUIT DIAGRAM (SCHEMATIC) FLASHLIGHTSWITCHLAMP+BATTERYThis simple schematic is the circuit of each flashlight. Place emphasis on ground, so that it is fully understood that ground = 0 volts.GROUNDGROUNDTWO GROUND SYMBOLS IS THE SAME AS CONNECTING WITH A WIREGROUND = 0 VOLTS
30DC Circuit Wiring Design three different DC circuits SwitchPowerSupplyBuzzerLightWired to turn Buzzer On/OffSwitchWired to turn Light On/OffPowerSupplyBuzzerLightSwitchWired to turn Light On in onedirection and Buzzer On in other directionPowerSupplyBuzzerLight
31Direct Current: Draw 3 different wiring test circuits SwitchPower+ 12FuseLightBuzzer
32Circuit to Switch Buzzer On / Off - Draw the rest of the wires Direct CurrentCircuit to Switch Buzzer On / Off - Draw the rest of the wiresSwitchPower+ 12FuseBuzzer OnLightBuzzer
33Circuit to Switch Buzzer On / Off Direct CurrentAnswerCircuit to Switch Buzzer On / OffSwitchPower+ 12FuseBuzzer OnLightBuzzer
34Draw Circuit to Switch Light On / Off Direct CurrentDraw Circuit to Switch Light On / OffSwitchPower+ 12FuseLight OnLightBuzzer
35Draw Circuit to Switch Light On / Off Direct CurrentAnswerDraw Circuit to Switch Light On / OffSwitchPower+ 12FuseLight OnLightBuzzer
36Direct Current Switch Power Fuse + 12 Light On Buzzer On Light Buzzer Draw Circuit to Turn Buzzer on in one Direction and Light in other DirectionSwitchPower+ 12FuseLight OnBuzzer OnLightBuzzer
37Direct Current Switch Power Fuse + 12 Light On Buzzer On Light Buzzer AnswerDraw Circuit to Turn Buzzer on in one Direction and Light in other DirectionSwitchPower+ 12FuseLight OnBuzzer OnLightBuzzer
38Electronic Components MicrophoneSound → CurrentBatteriesIn voltsResistorIn OhmsInductor or CoilIn henries+Power SupplyOutputs VoltsPass around componentsPotentiometerVariableResistorTransformerInput voltageSpeakerCurrent → Sound120VAC InDCvoltsOutIsolatedCapacitorsIn FaradsStepDown+StepUp
39Electronic Components DiodePN junction. Current flows in direction of arrow onlyTransistorElectronic Switch. Emitter, Base & Collector terminals. Small current (B-E) controls a larger one (C-E). Made of N (negative) and P (positive) sectionsSwitchNormally Open (n.o.)Normally Closed (n.c.)Anode (P)Cathode (N)n.o.n.c.PNPLEDLightEmittingDiodeSlide SwitchCan connect the center Pole to one of two Throws (SPDT)NPN(“Never Points iN”)PNP(“Points iN Proudly”)MetersCurrent MeterVoltage MeterResistance MeterBonus Question: Which type is the Transistor on the Electronics Merit Badge?
40Resistor Color Rings A Resistor’s value is indicated by its color bands and is measured in ohmsFirst Ring is First number / Closest to edge of resistorSecond Ring is second numberThird Ring is number of zerosFourth Ring is tolerance 1% or 5% or 10% etc.A Fifth Ring, if present, could indicate reliability or temperature sensitivityResistor Color Code ValuesPass around resistor slide ruleFirst RingBlack = 0Brown = 1Red = 2Orange = 3Yellow = 4Green = 5Blue = 6Violet = 7Gray = 8White = 9Second RingBlack = 0Brown = 1Red = 2Orange = 3Yellow = 4Green = 5Blue = 6Violet = 7Gray = 8White = 9Third Ring MultiplierSilver = XGold = XBlack = XBrown = XRed = 2 = XOrange = 3 = X ,000Yellow = 4 = X ,000Green = 5 = X ,000Blue = 6 = X 1,000,000Violet = 7 = X 10,000,000Fourth RingBrown = +/- 1%Red = +/- 2%Gold = +/- 5%Silver = +/- 10%None = +/- 20%
41G-Rated Resistor Color Code Mnemonics Black Brown Red Orange Yellow Green Blue Violet Gray White (Gold Silver None)Big Brown Rabbits Often Yield Great Big Vocal Groans When Gingerly SlappedBig Bears Run Over Your Gladiola Bed Vexing Garden WormsBlack Bears Run Over Yellow Grass, But Vultures Glide over WaterBetter Be Right Or Your Great Big Venture Goes WestBye Bye Rosie Off You Go to Birmingham Via Great WesternBlack Bart's Rambler Over Yonder Gave Bad Vibes Going WestBright Boys Rave Over Young Girls But Veto Getting WedBig Boys Race Our Young Girls Behind Victory Garden WallsBig Boys Race Our Young Girls But Violet Generally WinsBlack Birds Ruin Our Yellow Grain, Butchering Very Good WheatBilly Brown Ran Over a Yodeling Goat Because Violet's Granny Was GrumpyBad Betty Runs Over Your Garden But Violet Gray Won'tBilly Brown Revives On Your Gin, But Values Good WhiskyBetter Be Ready, Or Your Great Big Venture Goes WestBlack Beetles Running On Your Garden Bring Very Good WeatherBowling Balls Roll Over Your Grandpa But Victim Gets WellBatman Bests Robin On Yonder Gotham Bridge; Very Good, Will Get Superman Next!Badly Burnt Resistors On Your Ground Bus Void General WarranteeBig Bart Rides Over Your Grave Blasting Violent Guns WildlyBad Borg Raid Our Young Galaxy Before Vaporizing Good WalterI can’t say the one I use here!
42Resistor Value Examples RingBlack = 0Brown = 1Red = 2Orange = 3Yellow = 4Green = 5Blue = 6Violet = 7Gray = 8White = 9First Ring is first digitSecond Ring is second digitThird Ring is number of zerosExample of Color RingsFirst RingRed = 2Black = 0Second RingRed = 2Third RingRed = X = ohmsBrown = X = ohmsBrown=1, Green=5, Brown=x10, Tolerance=+/- 20%, Resistance=150 OhmsGreen=5, Red=2, Yellow=x10,000, Tolerance=+/- 20%, Resistance=520 kOhmsTest of Color RingsFirst RingBrown = ____Green = ____Second RingGreen = ____Red = ____Third RingBrown = ____ = ___ ohmsYellow = _____ = ____ ohms
43Resistor Value Examples AnswerRingBlack = 0Brown = 1Red = 2Orange = 3Yellow = 4Green = 5Blue = 6Violet = 7Gray = 8White = 9First Ring is first digitSecond Ring is second digitThird Ring is number of zerosExample of Color RingsFirst RingRed = 2Black = 0Second RingRed = 2Third RingRed = X = ohmsBrown = X = ohmsBrown=1, Green=5, Brown=x10, Tolerance=+/- 20%, Resistance=150 OhmsGreen=5, Red=2, Yellow=x10,000, Tolerance=+/- 20%, Resistance=520 kOhmsTest of Color RingsFirst RingBrown = 1Green = 5Second RingGreen = 5Red = 2Third RingBrown = x10 = ohmsYellow = x10,000 = 520k ohms
44Transistors Transistor Switch Circuit Mechanical Switch Circuit A Transistor is an Electronic SwitchTransistor come indifferent sizes dependingon the amount of currentand voltage requiredTransistorNPNSwitchMechanical Switch CircuitTransistor Switch CircuitDigital example. For analog, a small B-E current can control a larger CE current.Light12 VoltBatterySwitch openLight off = 0Switch closeLight on = 112 VoltBatteryNPN TransistorComputer cansend a signal to turnon the transistor whichthen turns on the light
45Draw, Label and Explain this Schematic This is the kit we will build in the last class. Have the students draw it on another piece of paper.
46Integrated CircuitsAn integrated circuit (IC) consists of multiple transistors. The number of transistors can vary from just a few (circuits shown below), to over two billion that are in the latest Intel microprocessor.This IC has 6 invertersAn inverter contains6 Transistors = 36 totalFunctionsInvertersGatesFlip flopsCountersMemoryMPUWatch ICsCalculators ICsMicrowave Timer ICsRadio ICsDialer ICsCar Controller ICs6 Transistors in one ICWhat type transistors? NPN or PNP?Inverter changes 0 to 1, 1 to 0.
47Insets: Wafer of Intel® Xeon™ processors and Gordon Moore, co-founder of Intel and author of Moore’s Law
48Microprocessor Integrated Circuit: 60,000 Transistors End of Class 1
49Education & Certification Required for Engineering Careers Engineering Assistant6 months to 2 years of Technical School during or after High SchoolEntry-Level Design Engineer4-year Bachelor of Science in Engineering DegreeSenior-Level Design Engineer, Engineering Manager4-year BS Degree, 2-year MS Degree2-20 years experienceSome Engineering Positions Require State Registration (P.E.)Professor, University or Industry R&D Laboratory ResearcherPh. D. or Sc. D. Degree in Physics or Engineering
50From the American Society for Engineering Education, 2009 US Numbers by TypeFrom the American Society forEngineering Education, 2009(http://www.asee.org)
51US BS Engineering Graduates By School, 2009 (Source: ASEE) Mostly state schools (nothing wrong with that!)
52US News & World Report 2011 US Undergraduate Engineering School Rankings (with Ph. D. Program) School ( * = public)1Massachusetts Institute of Technology2Stanford University (CA)3University of California, Berkeley*4California Institute of Technology5Georgia Institute of Technology*6University Of Illinois, Urbana-Champaign*University of Michigan, Ann Arbor*8Carnegie Mellon University (PA)9Cornell University (NY)Purdue University (IN)*50% state schools in top 10
53Starting SalariesTop Jobs for 2010 Bachelor’s Graduates (www.jobweb.com)
54About Joe Mulcahey Before College College Raytheon (since 1981) Built lots of Heathkits, installed an intercom and an alarm system in my tree house, performed various dangerous high-voltage experimentsStudied, passed FCC tests and became an amateur radio operatorStudied some more and passed more FCC tests, got a commercial radio operator’s license enabling me to work as a studio and transmitter engineer at a 50,000 Watt radio station in HartfordCollegeCo-op student at Raytheon in the Antenna and Microwave DepartmentEarned the BSEE and MSEE degrees from MIT in 1984Raytheon (since 1981)My specialty is designing and testing really big and expensive phased array radar antennas for missile defenseRaytheon is an industry leader in defense and government electronics, space, information technology, technical services, business aviation and special mission aircraft, with more than 71,000 employees world-wide, including over 30,000 engineers
55About Len Barrett Learned Aviation Electronics in the Navy Worked in an Electronics repair shopCGR and Siemens: Serviced x-ray equipment, CT scanners and MRI scannersGot a business degree from NortheasternCurrently at Aramark: Technology Manager in South Shore Hospital’s Clinical Engineering Department
56About Sean Mulcahey Eagle Scout with Gold Palm, 2009 Merit Badges earned: Electronics, Engineering, Radio, Energy, Computers and 26 othersCrew Guide, Venturing Crew 748NEU Sophomore in Electrical EngineeringCurrently on co-op at Bose, in the Product Safety LaboratoryTest returned and not-yet-released products for safetyTake expensive and fragile audio equipment and set it on fire, apply massive overvoltages, shake and drop
57Now go get some hands-on experience! Test EquipmentPower SupplyPower Equipment or Components for TestVolt-Ohm Meter (VOM) or Digital Volt Meter (DVM)Check AC & DC Voltages, Resistance, Opens/ShortsMay also Measure Capacitance, Inductance, Gain, etc.OscilloscopeGraphs one Voltage vs. Time or vs. another VoltageRadio Equipment TestingSignal GeneratorReceiverPower MeterSpectrum AnalyzerGraphs Voltage versus FrequencyNetwork AnalyzerField Strength MeterNow go get some hands-on experience!End of Class 2
58SolderingSafety Note: A Soldering Iron gets hotter than 300 F. Do not touchthe soldering iron’s metal parts or you will receive a third degree burnA good solder joint depends on the following:1) Solder iron must have a clean, well-tinned tip2) Parts to be soldered must be clean3) There must be a sound mechanical joint4) Parts to be soldered must be well heated before applying solder5) Wait approx. 5 seconds after soldering to allow strong mechanicaljoint to form
59Soldering – Heating Junction IronIronWireWirePC BoardWrongwayPC BoardRightwayIronSolder melts at 310° F. The wire and PC (Printed Circuit) board must be the same temperature for the solder to melt on both items.WirePlace soldering iron so that it touches both the PC board and wire. The heat from the soldering iron will transfer to the PC board and wire at the same time.PC Board
60Soldering – Applying Solder When the board and wire are hot enough the solder will flow and create a cone shape. Ifthe board is not hot enough the solder will be rounded on the board creating somewhatof a ball. The finishing solder should also be shiny. Clip extra wire at board level.WrongwayWireIronAfter 3 seconds place the solder on the tip of the iron, the wire and the PC board all together.The solder should flow to everything making a good connection.SolderPC BoardWireIronWireRightwayPC BoardSolderPC Board
61Un-SolderingUse pliers to hold the component next to the lead to be unsoldered (If the lead is held with the pliers it will draw heat from the lead)Apply soldering iron tip to PC board and wireEither use solder wick or solder sucker to draw solder off the board, or simply pull wire from PC board when hotThe soldering iron will damage electronic components if left on device for greater than 15 seconds, so work quicklySometimes it helps to put more solder on the solder joint to improve the thermal conductivityClean the soldering iron tip and keep it shiny
62Un-Soldering Iron Wire With pliers, hold device close to lead that is to be unsoldered. As heat is applied from soldering iron, pull with pliers. With one side out, do the same on other side.PC BoardIronPliersPC Board
63Kit Assembly Wrong Correct Red + Black 1) Place components into PC board in the order recommended on instructionsheet2) When components are placed into PC board, bend leads out slightly tokeep parts from falling out, when the PC board is turned over for soldering.3) Follow instructions as to proper orientation of components.PC BoardWrongClip wire at boardCorrectRed+LEDNote Flat EdgeBlack
66Anode of LED1 The Oscilloscope is displaying plots of voltage vs. time Q1 and Q2 are connected in a criss-cross fashion making a square wave oscillator running at about 1.5 Hz. The frequency is determined by C1 and R6. (Also C2 and R4.)The Oscilloscope is displaying plots of voltage vs. time
67C2 Negative, Q2 BaseWhen Q1 conducts, Q2 gets turned off until the voltage at Q2 base rises above about 0.7V. C2 has to discharge through R4 for this to happen. This determines the time the multi-vibrator will stay in one state.
68IC1 pin 2 & 6IC1 is also an oscillator that drives the speaker at a frequency that we can hear. It oscillates at either the low tone of about 720 Hz or the high tone of about 980 Hz. C4 charges through R5 but discharges through R9.
69IC1 pin 3This shows pin 3 of IC1 that drives the speaker. This oscilloscope shot captured the 985 Hz tone. The output at pin 3 is a square wave (almost).End of Class 3