29-06-2012, 12:43 PM
Beginners Guide to Electronics
[attachment=26073]
INTRODUCTION
I first became interested in electronics when I was age 10 (as long ago as 1961). In those days, transistors were only just being introduced and most equipment still used thermionic valves or “tubes” as the Americans would call them. Much of my learning was by practical experiment. I blew my Dad up only once by connecting 350 volt capacitors the wrong way round; electrocuted the window cleaner (but not fatally) and gave myself several high voltage shocks during the learning experience. This is not to be recommended so just remember that voltages in excess of 50 volts can be painful, if not downright dangerous. Anyway, I hope you enjoy my book. I guarantee it will be more interesting than any previous electronics course at school or college and you’ll understand how the components work after just a few minutes - not the fifteen years it took me to get a grip on it!
What's the Difference between A.C. and D.C.?
Everyone knows a battery or cell gives "d.c." or "direct current" and even though these letters do not mention the word "voltage" they actually mean "steady voltage." to power your radio or whatever. Less understood is "a.c." which stands for "alternating current" and this actually means a rising and falling voltage. It's important to understand the difference. You wouldn't connect your 12 volt radio directly to a mains power plug because you know the plug delivers 110v or 230 volts, depending on which country you live. Let's take a quick look at the method of making electricity. In a power station, electricity can be made most easily by using a gas or steam turbine or water impeller to drive a generator consisting of a magnet spinning inside a set of coils. The resultant voltage is always "alternating" by virtue of the magnet's rotation. Fig.1 indicates how the voltage rises positive then goes negative. Now, alternating voltage can be carried around the country via cables far more effectively than direct current because AC can be passed through a transformer and a high voltage can be reduced to a low voltage, suitable for use in homes.
How does a Resistor Work?
Imagine water flowing through a pipe. If we make the pipe narrow then this will restrict the flow of water. If we force the water (current) through the narrow gap by increasing the pressure (voltage) then energy will be given off as heat. In addition, there will be a significant difference in pressure (voltage) above and below the restriction. As an example, imagine pumping up a tyre by hand. The narrow pipe of the pump gets hot doesn’t it? In electronics we use a resistor when we need to reduce the voltage across the terminals of a circuit. This reduced voltage will cause a lower current to flow.
Resistor Colour Code
The value of a resistor is either printed in normal characters or, more usually, as coloured bands. Here is an example. The first band is red, indicating the number 2. The second band is also red, indicating 2. The third band is yellow, indicating 4 zeros. The fourth band is gold, indicating 5% tolerance. (Silver would indicate 10%, brown = 1%, red = 2%) This resistor is 220,000 Ohms in value, often written as 220k. As the tolerance is 5%, the actual resistance lies between 209000 and 231000 or 209k and 231k due to manufacturing inaccuracies. Take a box of resistors. Work out the value of each then check with a meter to see if you are correct. Note that the last band on the resister indicates the tolerance.
[attachment=26073]
INTRODUCTION
I first became interested in electronics when I was age 10 (as long ago as 1961). In those days, transistors were only just being introduced and most equipment still used thermionic valves or “tubes” as the Americans would call them. Much of my learning was by practical experiment. I blew my Dad up only once by connecting 350 volt capacitors the wrong way round; electrocuted the window cleaner (but not fatally) and gave myself several high voltage shocks during the learning experience. This is not to be recommended so just remember that voltages in excess of 50 volts can be painful, if not downright dangerous. Anyway, I hope you enjoy my book. I guarantee it will be more interesting than any previous electronics course at school or college and you’ll understand how the components work after just a few minutes - not the fifteen years it took me to get a grip on it!
What's the Difference between A.C. and D.C.?
Everyone knows a battery or cell gives "d.c." or "direct current" and even though these letters do not mention the word "voltage" they actually mean "steady voltage." to power your radio or whatever. Less understood is "a.c." which stands for "alternating current" and this actually means a rising and falling voltage. It's important to understand the difference. You wouldn't connect your 12 volt radio directly to a mains power plug because you know the plug delivers 110v or 230 volts, depending on which country you live. Let's take a quick look at the method of making electricity. In a power station, electricity can be made most easily by using a gas or steam turbine or water impeller to drive a generator consisting of a magnet spinning inside a set of coils. The resultant voltage is always "alternating" by virtue of the magnet's rotation. Fig.1 indicates how the voltage rises positive then goes negative. Now, alternating voltage can be carried around the country via cables far more effectively than direct current because AC can be passed through a transformer and a high voltage can be reduced to a low voltage, suitable for use in homes.
How does a Resistor Work?
Imagine water flowing through a pipe. If we make the pipe narrow then this will restrict the flow of water. If we force the water (current) through the narrow gap by increasing the pressure (voltage) then energy will be given off as heat. In addition, there will be a significant difference in pressure (voltage) above and below the restriction. As an example, imagine pumping up a tyre by hand. The narrow pipe of the pump gets hot doesn’t it? In electronics we use a resistor when we need to reduce the voltage across the terminals of a circuit. This reduced voltage will cause a lower current to flow.
Resistor Colour Code
The value of a resistor is either printed in normal characters or, more usually, as coloured bands. Here is an example. The first band is red, indicating the number 2. The second band is also red, indicating 2. The third band is yellow, indicating 4 zeros. The fourth band is gold, indicating 5% tolerance. (Silver would indicate 10%, brown = 1%, red = 2%) This resistor is 220,000 Ohms in value, often written as 220k. As the tolerance is 5%, the actual resistance lies between 209000 and 231000 or 209k and 231k due to manufacturing inaccuracies. Take a box of resistors. Work out the value of each then check with a meter to see if you are correct. Note that the last band on the resister indicates the tolerance.