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Introduction to Electronics - Fourth session

This document summarizes two review sessions on practical circuits. It introduces capacitors, diodes, LEDs, transistors, integrated circuits and other components. It then describes two circuits built in the first session, including their parts lists. The second session discusses modifying the second circuit by changing resistor values and adding a potentiometer to control the blinking rate of an LED. It then introduces the third circuit using a 555 timer IC to create an oscillator. Instructions are provided on modifying this circuit to add a volume control.

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Introduction to Electronics November 12, 2015
Fourth Session Review Practical Circuits
Review
Review ● Capacitors ● Diodes ● LEDs ● Wire ● Transistors ● Integrated Circuits ● Potentiometer ● Inductors
First Circuit
First circuit Parts List: 1K ohm - 1/4 Watt resistor 5mm red LED SPST toggle switch 9V battery connector
First Circuit
Second Circuit
Second Circuit Parts List: 2N3904 PNP transistor 2N3906 NPN transistor 47 ohm - 1/4 Watt resistor 1K ohm - 1/4 Watt resistor 470K ohm - 1/4 Watt resistor 10uF electrolytic capacitor Optional: 10K ohm - 1/4 Watt resistor 1M potentiometer
Second Circuit Any general purpose NPN or PNP transistors should do for the circuit, but should you want to follow along at home, I am using 293904 (NPN) and 2N3906 (PNP) transistors. I learned their pin layouts by looking up their datasheets. A good source for quickly finding datasheets is Octopart.com. Simply search for the part number and you should find a picture of the part and link to the datasheet.
Second Session
Second Circuit try changing the value of 470K resistor. Notice that by increasing the value of this resistor, the LED blinks slower and that by decreasing it, the LED blinks faster. The reason for this is that the resistor is controlling the rate at which the 10uF capacitor is filling and discharging. This is directly related to the blinking of the LED. Replace this resistor with a 1M potentiometer that is in series with a 10K resistor. Wire it such that one side of the resistor connects to an outer pin on the potentiometer and the other side connects to the base of the PNP transistor. The center pin of the potentiometer should connect to ground. The rate of blinking now changes when you turn the knob and sweep through the resistance.
Second Session
Third Circuit
Third Circuit Parts List: 555 Timer IC 1K ohm - 1/4 Watt resistor 10K ohm - 1/4 Watt resistor 1M ohm - 1/4 Watt resistor 10uF electrolytic capacitor 0.01uF ceramic disc capacitor
Third Circuit You can read all about 555 chips on this page and see a great selection of additional 555 schematics on this page.
Third Circuit
Third Circuit If you want to take it a step farther, you can create a volume knob by connecting one outer pin of a 100K potentiometer to pin 3, the middle pin to the speaker, and the the remaining outer pin to ground.
Okay... You are not exactly on your own. The internet is full of people who know how to do this stuff and have documented their work such that you can learn how to do it as well. Go forth and seek out what you want to make. If the circuit does not yet exist, chances are there is documentation of something similar already online. A great place to start finding circuit schematic is the Discover Circuits site. They have a comprehensive list of fun circuits to experiment with.