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Electronics Merit Badge

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1 Electronics Merit Badge
Old Colony Council Merit Badge University March 2012 Joe Mulcahey Len Barrett Sean Mulcahey Mention optional kit=$10 (same or equivalent required to complete badge) Homework: read MB pamphlet, bring in questions Rev. S, 01MAR12 Based on the Electronics Merit Badge classes taught at the 2005 & 2010 National Jamborees

2 Electronics Merit Badge Class Outline
Class 1 Safety (Requirement 1) March 3 Electricity & Electronics Introduction Circuit 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)

3 Safety 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?

4 Electricity Safety High Voltage ( 120V AC or greater) – Safety mainly about not touching the wrong thing Current kills – Only 16 volts can kill when enough electrons flow through the heart or head Ventricular fibrillation – Electrons passing through the heart causes muscles to seize, leading to death If the shock doesn’t kill you, you can still be badly burned from touching the wrong thing Shock can be avoided by being educated about potentially dangerous situations. Stay away from them!!!

5 How to Avoid Shock Turn power off before working on equipment
Don’t touch circuits that could have high voltage on them Do not allow electrons to flow through the heart. I don’t think the snake knew about this detail The 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.

6 Electronics Safety Electronics generally uses lower voltages (less than 48 volts) You are usually working with DC voltage instead of AC voltage You are usually more concerned with sparks from connecting the wrong wires together, or burning yourself with a soldering iron, or some similar event Even when working with lower voltages, you may still receive an electrical shock from equipment you are using Emphasis here is that electronics is inherently safer than electricity, because the voltages are much smaller. This does not diminish the necessity for safety.

7 Personal Safety Be aware of what you are doing, and where you are placing equipment and yourself Pay attention to hot soldering irons Keep a good distance between you and those next to you Know when you are working with high current and/or high voltage circuits THINK before you do something Wear safety glasses when soldering

8 One Hand Rule Prevents current from flowing in one arm, through your heart, and out the other arm Keep one hand in your pocket!

9 Introduction to Electronics
Electrical and Electronics Engineering are both career fields that are involved with Electronics Technology Electrical engineers specializing in power work with motors and generators, and design transmission lines and power plants EEs specializing in electronics deal with communications, such as radio, television and telephony, radar and digital & analog circuit technologies All engineers draw from the fundamentals of science and mathematics They design and work with electrical, electronic, electro-optical, and electromechanical devices, circuits, and systems

10 Introduction (Continued)
Electrical Engineers collaborate with other professionals in developing sophisticated software tools that support design, verification, and testing Electrical 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 manufacturing In 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)

11 Types 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: Lightning Combing hair Walking across carpet and getting shocked Pulling out scotch tape

12 Types 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 house Home air conditioners

13 Types 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 players Radios Electricity in cars Anywhere you use a battery for power

14 Basics 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 AMP Current: Electrical symbol for current is I

15 Current Flow – Water Analogy
Water flows in the hose, entering at the top and exiting the bottom The water is the “current”; the flow of electrons The more water flowing in the pipe, the more electrons are flowing in the wire Different pipe diameters illustrates different resistance to water flow, which correlates to different resistor values Get 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.

16 Current Current: Defined as “flow of electrons”
Current: Units of current is the AMP Current: Electrical symbol for current is I Common units for current are: amps milliamps (mA): 1 mA = amp microamps (mA) : 1 mA = amp, or mA nanoamps (nA) : 1 nA = amp, mA, or mA It 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.

17 Voltage – Water Analogy
Small height = low voltage Big height = high voltage height This is a very important concept to get across. Voltage, current and resistance are the basis for this class. height Gravity provides the force for water (current) to flow This illustrates a small voltage, so electron flow is small Gravity provides the force for water (current) to flow This illustrates a larger voltage, so electron flow is larger

18 Voltage Volts is the electrical force that causes
electrons (current) to flow Units of volts is the VOLT The symbol of volts is E or V. We will use V Common units for voltage are: volts Millivolt (mv) : volt Microvolt (mv) : volt, or mV Nanovolt (nv) : volt, mV, or mV

19 Resistance – Water Analogy
10000Ω Different pipe diameters represents different resistor values The smaller the diameter of the pipe, the larger the resistance 1000Ω 100Ω 10Ω

20 Resistance Resistance is an electrical property of a material that “resists” the flow of electrons The schematic symbol for a resistor is: Common units for resistance are: ohms kiloohm: 1KΩ = 1000 ohms, 10KΩ = 10,000 ohms megaohm: 1MΩ = 1,000,000 ohms The 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.

21 Power – Water Analogy In electronics, power is equal to current X voltage The units for power is the WATT The symbol for power is W or P In our water analogy, power is equal to water flow X pressure You can see from the picture that more water flow will mean more force, and more pressure will mean more force

22 Ohm’s Law One of the most important laws in electronics/electricity
V = I x R : Voltage = Current x Resistance Voltage is measure in volts, current is measured in amps, and resistance is measured in ohms 1 amp, going through 1 ohm of resistance, results in a voltage drop of 1 volt 1 V = 1 A x 1 Ω Ohms’s law is the purpose of this class. Clear understanding of current and voltage and resistance is key in making ohm’s law comprehensible.

23 More Ohm’s Law Different forms of Ohm’s Law:
V = I x R : Voltage = Current X Resistance I = V / R : Current = Voltage / Resistance R = V / I : Resistance = Voltage / Current Make 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 = 10 Resistance = 1000Ω Compute current: I = V / R I = 10 / 1000 = .01A .01A = 10mA Question: what would the current be if the voltage was 1 V? How about 1000 V? + 10V 1000 Ω

24 Ohm’s Law Pie Chart If you know any two values, you can get the other two with these formulas

25 Bonus Ohm’s Law Question: Resistor Cube
Resistances in series add: RTotal=2R Resistance between points A and B = 5/6 Ohms Would take the typical second-year EE student about 8 pages of work to solve. Resistances in parallel divide: RTotal=R/2 What is the resistance between points A and B?

26 Where Did the Names of the Electrical Parameters Come From?
Volts: Count Alessandro Volta ( ), Italian Scientist Ohms: Georg Simon Ohm ( ), German Physicist Amps: André-Marie Ampère ( ), French Physicist Watts: James Watt ( ), British Engineer Farads: Michael Faraday ( ), British Physicist Henrys: Joseph Henry ( ), American Physicist Other Units: Coulomb, Gauss, Joule, Tesla and of course Smoot

27 Smoot? 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.

28 Electronic Symbols Single Pole, Double Throw Switch (SPDT) Battery
NC W Single Pole, Double Throw Switch (SPDT) NO Battery Capacitor or Resistor Light Emitting Diode (LED) Buzzer Ground Fuse Lamp

FLASHLIGHT SWITCH LAMP + BATTERY This simple schematic is the circuit of each flashlight. Place emphasis on ground, so that it is fully understood that ground = 0 volts. GROUND GROUND TWO GROUND SYMBOLS IS THE SAME AS CONNECTING WITH A WIRE GROUND = 0 VOLTS

30 DC Circuit Wiring Design three different DC circuits
Switch Power Supply Buzzer Light Wired to turn Buzzer On/Off Switch Wired to turn Light On/Off Power Supply Buzzer Light Switch Wired to turn Light On in one direction and Buzzer On in other direction Power Supply Buzzer Light

31 Direct Current: Draw 3 different wiring test circuits
Switch Power + 12 Fuse Light Buzzer

32 Circuit to Switch Buzzer On / Off - Draw the rest of the wires
Direct Current Circuit to Switch Buzzer On / Off - Draw the rest of the wires Switch Power + 12 Fuse Buzzer On Light Buzzer

33 Circuit to Switch Buzzer On / Off
Direct Current Answer Circuit to Switch Buzzer On / Off Switch Power + 12 Fuse Buzzer On Light Buzzer

34 Draw Circuit to Switch Light On / Off
Direct Current Draw Circuit to Switch Light On / Off Switch Power + 12 Fuse Light On Light Buzzer

35 Draw Circuit to Switch Light On / Off
Direct Current Answer Draw Circuit to Switch Light On / Off Switch Power + 12 Fuse Light On Light Buzzer

36 Direct Current Switch Power Fuse + 12 Light On Buzzer On Light Buzzer
Draw Circuit to Turn Buzzer on in one Direction and Light in other Direction Switch Power + 12 Fuse Light On Buzzer On Light Buzzer

37 Direct Current Switch Power Fuse + 12 Light On Buzzer On Light Buzzer
Answer Draw Circuit to Turn Buzzer on in one Direction and Light in other Direction Switch Power + 12 Fuse Light On Buzzer On Light Buzzer

38 Electronic Components
Microphone Sound → Current Batteries In volts Resistor In Ohms Inductor or Coil In henries + Power Supply Outputs Volts Pass around components Potentiometer Variable Resistor Transformer Input voltage Speaker Current → Sound 120V AC In DC volts Out Isolated Capacitors In Farads Step Down + Step Up

39 Electronic Components
Diode PN junction. Current flows in direction of arrow only Transistor Electronic Switch. Emitter, Base & Collector terminals. Small current (B-E) controls a larger one (C-E). Made of N (negative) and P (positive) sections Switch Normally Open (n.o.) Normally Closed (n.c.) Anode (P) Cathode (N) n.o. n.c. PNP LED Light Emitting Diode Slide Switch Can connect the center Pole to one of two Throws (SPDT) NPN (“Never Points iN”) PNP (“Points iN Proudly”) Meters Current Meter Voltage Meter Resistance Meter Bonus Question: Which type is the Transistor on the Electronics Merit Badge?

40 Resistor Color Rings A Resistor’s value is indicated
by its color bands and is measured in ohms First Ring is First number / Closest to edge of resistor Second Ring is second number Third Ring is number of zeros Fourth Ring is tolerance 1% or 5% or 10% etc. A Fifth Ring, if present, could indicate reliability or temperature sensitivity Resistor Color Code Values Pass around resistor slide rule First Ring Black = 0 Brown = 1 Red = 2 Orange = 3 Yellow = 4 Green = 5 Blue = 6 Violet = 7 Gray = 8 White = 9 Second Ring Black = 0 Brown = 1 Red = 2 Orange = 3 Yellow = 4 Green = 5 Blue = 6 Violet = 7 Gray = 8 White = 9 Third Ring Multiplier Silver = X Gold = X Black = X Brown = X Red = 2 = X Orange = 3 = X ,000 Yellow = 4 = X ,000 Green = 5 = X ,000 Blue = 6 = X 1,000,000 Violet = 7 = X 10,000,000 Fourth Ring Brown = +/- 1% Red = +/- 2% Gold = +/- 5% Silver = +/- 10% None = +/- 20%

41 G-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 Slapped Big Bears Run Over Your Gladiola Bed Vexing Garden Worms Black Bears Run Over Yellow Grass, But Vultures Glide over Water Better Be Right Or Your Great Big Venture Goes West Bye Bye Rosie Off You Go to Birmingham Via Great Western Black Bart's Rambler Over Yonder Gave Bad Vibes Going West Bright Boys Rave Over Young Girls But Veto Getting Wed Big Boys Race Our Young Girls Behind Victory Garden Walls Big Boys Race Our Young Girls But Violet Generally Wins Black Birds Ruin Our Yellow Grain, Butchering Very Good Wheat Billy Brown Ran Over a Yodeling Goat Because Violet's Granny Was Grumpy Bad Betty Runs Over Your Garden But Violet Gray Won't Billy Brown Revives On Your Gin, But Values Good Whisky Better Be Ready, Or Your Great Big Venture Goes West Black Beetles Running On Your Garden Bring Very Good Weather Bowling Balls Roll Over Your Grandpa But Victim Gets Well Batman Bests Robin On Yonder Gotham Bridge; Very Good, Will Get Superman Next! Badly Burnt Resistors On Your Ground Bus Void General Warrantee Big Bart Rides Over Your Grave Blasting Violent Guns Wildly Bad Borg Raid Our Young Galaxy Before Vaporizing Good Walter I can’t say the one I use here!

42 Resistor Value Examples
Ring Black = 0 Brown = 1 Red = 2 Orange = 3 Yellow = 4 Green = 5 Blue = 6 Violet = 7 Gray = 8 White = 9 First Ring is first digit Second Ring is second digit Third Ring is number of zeros Example of Color Rings First Ring Red = 2 Black = 0 Second Ring Red = 2 Third Ring Red = X = ohms Brown = X = ohms Brown=1, Green=5, Brown=x10, Tolerance=+/- 20%, Resistance=150 Ohms Green=5, Red=2, Yellow=x10,000, Tolerance=+/- 20%, Resistance=520 kOhms Test of Color Rings First Ring Brown = ____ Green = ____ Second Ring Green = ____ Red = ____ Third Ring Brown = ____ = ___ ohms Yellow = _____ = ____ ohms

43 Resistor Value Examples
Answer Ring Black = 0 Brown = 1 Red = 2 Orange = 3 Yellow = 4 Green = 5 Blue = 6 Violet = 7 Gray = 8 White = 9 First Ring is first digit Second Ring is second digit Third Ring is number of zeros Example of Color Rings First Ring Red = 2 Black = 0 Second Ring Red = 2 Third Ring Red = X = ohms Brown = X = ohms Brown=1, Green=5, Brown=x10, Tolerance=+/- 20%, Resistance=150 Ohms Green=5, Red=2, Yellow=x10,000, Tolerance=+/- 20%, Resistance=520 kOhms Test of Color Rings First Ring Brown = 1 Green = 5 Second Ring Green = 5 Red = 2 Third Ring Brown = x10 = ohms Yellow = x10,000 = 520k ohms

44 Transistors Transistor Switch Circuit Mechanical Switch Circuit
A Transistor is an Electronic Switch Transistor come in different sizes depending on the amount of current and voltage required Transistor NPN Switch Mechanical Switch Circuit Transistor Switch Circuit Digital example. For analog, a small B-E current can control a larger CE current. Light 12 Volt Battery Switch open Light off = 0 Switch close Light on = 1 12 Volt Battery NPN Transistor Computer can send a signal to turn on the transistor which then turns on the light

45 Draw, 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.

46 Integrated Circuits An 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 inverters An inverter contains 6 Transistors = 36 total Functions Inverters Gates Flip flops Counters Memory MPU Watch ICs Calculators ICs Microwave Timer ICs Radio ICs Dialer ICs Car Controller ICs 6 Transistors in one IC What type transistors? NPN or PNP? Inverter changes 0 to 1, 1 to 0.

47 Insets: Wafer of Intel® Xeon™ processors and Gordon Moore, co-founder of Intel and author of Moore’s Law

48 Microprocessor Integrated Circuit: 60,000 Transistors
End of Class 1

49 Education & Certification Required for Engineering Careers
Engineering Assistant 6 months to 2 years of Technical School during or after High School Entry-Level Design Engineer 4-year Bachelor of Science in Engineering Degree Senior-Level Design Engineer, Engineering Manager 4-year BS Degree, 2-year MS Degree 2-20 years experience Some Engineering Positions Require State Registration (P.E.) Professor, University or Industry R&D Laboratory Researcher Ph. D. or Sc. D. Degree in Physics or Engineering

50 From the American Society for Engineering Education, 2009
US Numbers by Type From the American Society for Engineering Education, 2009 (

51 US BS Engineering Graduates By School, 2009 (Source: ASEE)
Mostly state schools (nothing wrong with that!)

52 US News & World Report 2011 US Undergraduate Engineering School Rankings (with Ph. D. Program)
School ( * = public) 1 Massachusetts Institute of Technology 2 Stanford University (CA) 3 University of California, Berkeley* 4 California Institute of Technology 5 Georgia Institute of Technology* 6 University Of Illinois, Urbana-Champaign* University of Michigan, Ann Arbor* 8 Carnegie Mellon University (PA) 9 Cornell University (NY) Purdue University (IN)* 50% state schools in top 10

53 Starting Salaries Top Jobs for 2010 Bachelor’s Graduates (

54 About 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 experiments Studied, passed FCC tests and became an amateur radio operator Studied 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 Hartford College Co-op student at Raytheon in the Antenna and Microwave Department Earned the BSEE and MSEE degrees from MIT in 1984 Raytheon (since 1981) My specialty is designing and testing really big and expensive phased array radar antennas for missile defense Raytheon 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

55 About Len Barrett Learned Aviation Electronics in the Navy
Worked in an Electronics repair shop CGR and Siemens: Serviced x-ray equipment, CT scanners and MRI scanners Got a business degree from Northeastern Currently at Aramark: Technology Manager in South Shore Hospital’s Clinical Engineering Department

56 About Sean Mulcahey Eagle Scout with Gold Palm, 2009
Merit Badges earned: Electronics, Engineering, Radio, Energy, Computers and 26 others Crew Guide, Venturing Crew 748 NEU Sophomore in Electrical Engineering Currently on co-op at Bose, in the Product Safety Laboratory Test returned and not-yet-released products for safety Take expensive and fragile audio equipment and set it on fire, apply massive overvoltages, shake and drop

57 Now go get some hands-on experience!
Test Equipment Power Supply Power Equipment or Components for Test Volt-Ohm Meter (VOM) or Digital Volt Meter (DVM) Check AC & DC Voltages, Resistance, Opens/Shorts May also Measure Capacitance, Inductance, Gain, etc. Oscilloscope Graphs one Voltage vs. Time or vs. another Voltage Radio Equipment Testing Signal Generator Receiver Power Meter Spectrum Analyzer Graphs Voltage versus Frequency Network Analyzer Field Strength Meter Now go get some hands-on experience! End of Class 2

58 Soldering Safety Note: A Soldering Iron gets hotter than 300 F. Do not touch the soldering iron’s metal parts or you will receive a third degree burn A good solder joint depends on the following: 1) Solder iron must have a clean, well-tinned tip 2) Parts to be soldered must be clean 3) There must be a sound mechanical joint 4) Parts to be soldered must be well heated before applying solder 5) Wait approx. 5 seconds after soldering to allow strong mechanical joint to form

59 Soldering – Heating Junction
Iron Iron Wire Wire PC Board Wrong way PC Board Right way Iron Solder melts at 310° F. The wire and PC (Printed Circuit) board must be the same temperature for the solder to melt on both items. Wire Place 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

60 Soldering – Applying Solder
When the board and wire are hot enough the solder will flow and create a cone shape. If the board is not hot enough the solder will be rounded on the board creating somewhat of a ball. The finishing solder should also be shiny. Clip extra wire at board level. Wrong way Wire Iron After 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. Solder PC Board Wire Iron Wire Right way PC Board Solder PC Board

61 Un-Soldering Use 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 wire Either use solder wick or solder sucker to draw solder off the board, or simply pull wire from PC board when hot The soldering iron will damage electronic components if left on device for greater than 15 seconds, so work quickly Sometimes it helps to put more solder on the solder joint to improve the thermal conductivity Clean the soldering iron tip and keep it shiny

62 Un-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 Board Iron Pliers PC Board

63 Kit Assembly Wrong Correct Red + Black
1) Place components into PC board in the order recommended on instruction sheet 2) When components are placed into PC board, bend leads out slightly to keep parts from falling out, when the PC board is turned over for soldering. 3) Follow instructions as to proper orientation of components. PC Board Wrong Clip wire at board Correct Red + LED Note Flat Edge Black

64 Soldering Kit

65 From the Kit Manual

66 Anode 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

67 C2 Negative, Q2 Base When 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.

68 IC1 pin 2 & 6 IC1 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.

69 IC1 pin 3 This 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

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