Frequently Un asked Questions

1. Frequently Unasked Questions Loyola Blakefield Introduction to Engineering March 8, 2012 Bob Rassa, Raytheon Space & Airborne Systems RCRassa@Raytheon.com

2. Observations. . . • Many of you used “flow of electrons” in your narratives--- • This is true, technically, BUT to include that in your discussion is like discussing the car wheels going around when you describe driving. • Instead of saying that the electrons (or current) flows to the light bulb or the resistor etc when you turn on the power switch, you say that the bulb is illuminated when the switch is pressed (or similar) – in other words, describe the observable function vs. the internal workings. • We also don’t describe the functions of components as “translating energy flow around the circuit board” • We say “power is provided to” or “the signal goes to” • Buttons don’t “send power to” something; they Activate it

3. SPST L xtal + - C C + R - Symbols Variable Resistor Capacitor Variable Capacitor Inductor Battery Ground Switch Crystal

4. SPKR antenna D motor ZENER LED D More Symbols Transistors Motor Light-Emitting Diode Speaker Zener Diode Antenna Transformer Diode

5. And still more--- AC Plug Coaxial Connector Operational Amplifier (also Pre-amp, Amp)

6. Resistors etc • Resistors, capacitors and inductors have multiple functions in a circuit. • Resistors do generally limit the current in a circuit—but that isn’t always their function • Resistors, capacitors and inductors are also used in combination as: • Filters • Resonant Circuits • Timers

7. Diodes Transistors etc • Diodes are part of a class of devices known as semiconductors • Diodes pass current in one direction only • In DC circuits they block reverse current flow • In AC circuits they pass half of the voltage cycle • Transistors are also semiconductors • Transistors amplify current • Integrated circuits are semiconductors • ICs are primarily transistors, with some diodes- very few resistors are build into an IC • ICs are typically microprocessors – very small computers – but can be other things as well, such as simple logic controllers, random access memory (RAM), and more

8. Crystals & Oscillators • Resistors, capacitors and inductors are used in combinations as Oscillators – constructs that produce a higher-frequency alternating current (AC) signal • A Crystal is often used to more precisely control the frequency of the oscillator • Oscillators use the principle of resonance – a self-reinforcing electrical signal or sound wave- in a resonant circuit • Sound resonance is what you experience if you rub a wet finger around the rim of a wine glass, for example • Bass speakers work by installing them in a cabinet with a resonant frequency in the mid range of the speaker response - this resonant frequency response increases the speaker volume

9. Television and Radio TV and radios work by transmitting a carrier frequency that is modulated by the desired viewing or listening content. The original broadcast TV (Ch 2-13) operated in the frequency band – or spectrum - of 54 MHz (Megahertz) to 216 MHz. These are the VHF channels. In the middle, from 88 MHz to 108 MHz, is the FM radio spectrum. The UHF spectrum is from 470 MHz to 890 MHz (Ch 14 to 83) The base frequency is called the Carrier or Center frequency. The content signal (audio for FM, audio and video for TV) modulates the carrier frequency. To modulate means to cause it to vary according to the modulating signal. The TV or FM receiver uses a detector circuit to “demodulate” the signal, meaning decode the content from the carrier

10. Printed Circuit Boards Printed circuit boards are devices that hold electronic components and connect them together to perform a specific function or set of functions. The components mount on the top side (component side) and are soldered to the “printed trace” on the underside. The printed trace is the series of electrical “wires” that connect the components together. It is called a printed circuit board since the trace appears to be “printed” on the underside; in actuality it is acid-etched there from a solid conductive sheet and then coated with insulation. The spots on the trace where component leads protrude through and are soldered to the trace are called “pads”.

11. Functional Block Diagrams • A functional block diagram is a drawing that shows the basic and critical functions of a circuit. • It generally doesn’t use electrical symbols except as needed for clarity • It shows the basic flow of the circuit. Typical are: • Input power • Input signal • Antennas • Signal generating devices (e.g. microphone) • Signal amplifiers, controllers, processors • Feedback loops, if any • Relays, if any • Signal outputs • Grounds as needed for clarity (not necessary to show every one)

12. Example: Traffic Light The traffic light kit simulates the traffic signal at a 4-way intersection. The function of the device is to serve as a miniature of a real traffic signal. There are 12 LEDs in a 3-lamp configuration facing each direction, in traffic signal colors of red (top), yellow (middle) and green (bottom). The system has an adjustable timer circuit controlling the lights, which determines how long the lights stay red or green in each direction. Just as in a real traffic signal, the lights go from green to yellow and then red in one direction before the lights in the cross-traffic position change to green. The system is powered by a 9-volt battery and uses a microprocessor to control the timing, which is adjustable by a potentiometer.

13. Questions?