# Learn Electronics/Foreword

1. Aim of book: To make it possible for people to read this and start creating their own electronic devices and understanding them. Introducing theories only when they apply to what the reader is doing (follow the Keep It Short and Simple rule).
Although the Electronics wikibook has about the same goal, it introduces too many theories that don't apply to beginners and no hands-on experience, making it impossible to learn out of that book. Links to some theories in that book may be added so they are not replicated on both books, unless it needs to be shortened.
2. Prerequisites: Some knowledge of physics and math is assumed
3. Materials: You may want to consider getting the following materials: Breadboard, and a source of voltage to start with. (under construction)

# Sources of Direct current (DC) Voltage

* For simple hands-on experiences to learn about Electronics it is best to start with BATTERIES as a simple source of electricity. All sorts of types of batteries are available, and it is important to select the correct type for the particular usage.
** AN EXAMPLE:
I have 2 sets of 3-volt (two 1.5 volt each in series) D-size batteries, one new, call it black, and the other used, call it red. The open-circuit actual measured voltages are approximately Red=2.75 Volt, Black=2.97 Volt. Each of these sets of batteries has an internal resistance which can be calculated as follows:
..... Use a load resistance, but which? My ammeter has a range with a full-scale deflection of 0.5 Amperes, which I could get by using a resistor having about 3/0.5 = 6 Ohms (6 Ω). But I do not have such a resistor.
..... Using a 25 Ω resistor as a load, I get a current flow of 95 milliamperes (mA) from the black batteries. Calculating the total approximate resistance in circuit (internal plus external) 2.97/0.097=31.3 Ohms (total). Deduct the external 25 Ω, and get approximately 6 Ω for the internal resistance of the black battery set.
..... Using the same 25 Ω external resistor, I get a current flow of only 60 mA from the red batteries, which indicates an approximate internal resistance of (2.75/0.060) - 25 = 46 - 25 = 21 Ω.
* Another simple source of DC is a BATTERY CHARGER. This gets its energy from one of the sockets usually available at the bottom in every room. A battery charger starts off with Alternating Current (AC) derived from the mains/line via that socket, and, using one or more rectifiers, converts it into Direct Current (DC) whose voltage keeps changing very quickly all the time from zero to maximum and back again. Often a Capacitor, also sometimes called a Condenser, is used to "smooth" the available DC voltage, and the resulting DC. It is connected across the DC voltage source.
** An example of a battery charger with 3 different output circuits described on the label:
*** 1) for two or four AA, two or four C or two or four D rechargeable batteries (2.9V, 100 mA for two in series)
*** 2) for only one 9V rechargeable battery (9V, 5 mA), and
*** 3) for only one(?) AAA rechargeable battery (5.8V 18mA).
*** Some manufacturers have on the battery label their instruction showing for how long their rechargeable battery should be charged. Never attempt to "charge" any battery not labelled as being rechargeable - it may be dangerous.
* Many different types of adapters are available that supply either AC or DC for toys, players/recorders, etc. at the correct voltage as required. The correct adapter must be used for each purpose.

# Sources of Alternating current (AC) Voltage

* CAUTION! Using the wall socket as source can be very dangerous, and should be postponed until much is known about electricity, its uses, and safety measures associated with it.
* The voltage available at the wall socket is too high for elementary experimentation, but transformers are available that will reduce the voltage to non-dangerous levels. Look for adapters that also are available in many different types and AC voltages.
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