Understanding Basic Electronics: Voltage, Current, Resistors, Capacitors, and Transistors, Schemes and Mind Maps of Computer Vision

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Technology

Basic Electronics

HARVEY D. VILLALUNA BSIT – 1B

There are two types of electrical signals , those being alternating current (AC), and direct current (DC). With alternating current, the direction electricity flows throughout the circuit is constantly reversing. You may even say that it is alternating direction. The rate of reversal is measured in Hertz, which is the number of reversals per second. So, when they say that the US power supply is 60 Hz, what they mean is that it is reversing 120 times per second (twice per cycle). With Direct Current, electricity flows in one direction between power and ground. In this arrangement there is always a positive source of voltage and ground (0V) source of voltage. You can test this by reading a battery with a multimeter. For great instructions on how to do this, check out Ladyada's multimeter page (you will want to measure voltage in particular). Speaking of voltage, electricity is typically defined as having a voltage and a current rating. Voltage is obviously rated in Volts and current is rated in Amps. For instance, a brand new 9V battery would have a voltage of 9V and a current of around 500mA ( milliamps). Electricity can also be defined in terms of resistance and watts. We will talk a little bit about resistance in the next step, but I am not going to be going over Watts in depth. As you delve deeper into electronics you will encounter components with Watt ratings. It is important to never exceed the Wattage rating of a component, but fortunately that Wattage of your DC power supply can easily be calculated by multiplying the voltage and current of your power source. If you want a better understanding of these different measurements, what they mean, and how they relate, check out this informative video on Ohm's Law. Most basic electronic circuits use DC electricity. As such, all further discussion of electricity will revolve around DC electricity.

As the name implies, resistors add resistance to the circuit and reduces the flow of electrical current. It is represented in a circuit diagram as a pointy squiggle with a value next to it. The different markings on the resistor represent different values of resistance. These values are measured in ohms. Resistors also come with different wattage ratings. For most low-voltage DC circuits, 1/4 watt resistors should be suitable. You read the values from left to right towards the (typically) gold band. The first two colors represent the resistor value, the third represents the multiplier, and the fourth (the gold band) represents the tolerance or precision of the component. You can tell the value of each color by looking at a resistor color value chart. Or... to make your life easier, you could simply look up the values using a graphical resistance calculator. Anyhow... a resistor with the markings brown, black, orange, gold will translate as follows: 1 (brown) 0 (black) x 1,000 = 10,000 with a tolerance of +/- 5% Any resistor of over 1000 ohms is typically shorted using the letter K. For instance, 1,000 would be 1K; 3,900, would translate to 3.9K; and 470,000 ohms would become 470K. Values of ohms over a million are represented using the letter M. In this case, 1,000,000 ohms would become 1M.

Diodes are components which are polarized. They only allow electrical current to pass

through them in one direction. This is useful in that it can be placed in a circuit to prevent

electricity from flowing in the wrong direction.

Another thing to keep in mind is that it requires energy to pass through a diode and this

results in a drop of voltage. This is typically a loss of about 0.7V. This is important to keep in

mind for later when we talk about a special form of diodes called LEDs.

The ring found on one end of the diode indicates the side of the diode which connects to

ground. This is the cathode. It then follows that the other side connects to power. This side is

the anode.

The part number of the diode is typically written on it, and you can find out its various

electrical properties by looking up its datasheet.

They are represented in schematic as a line with a triangle pointing at it. The line is that side

which connected to ground and the bottom of the triangle connects to power.

A transistor takes in a small electrical current at its base pin and amplifies it such that a much larger

current can pass between its collector and emitter pins. The amount of current that passes between

these two pins is proportional to the voltage being applied at the base pin.

There are two basic types of transistors, which are NPN and PNP. These transistors have opposite

polarity between collector and emitter. For a very comprehensive intro to transistors check out this page.

NPN transistors allow electricity to pass from the collector pin to the emitter pin. They are represented in

a schematic with a line for a base, a diagonal line connecting to the base, and a diagonal arrow pointing

away from the base.

PNP transistors allow electricity to pass from the emitter pin to the collector pin. They are represented in

a schematic with a line for a base, a diagonal line connecting to the base, and a diagonal arrow pointing

towards the base.

Transistors have their part number printed on them and you can look up their datasheets online to learn

about their pin layouts and their specific properties. Be sure to take note of the transistor's voltage and

current rating as well.