Hi and welcome to iThePro. This tutorial is about arduino and we going to learn some basics things together. In this Part we going to see some Electronics Background.

Let start with the basics about voltage, current and resistance. These three components come together in the Ohm's Law, which is the key to understanding a circuit. Ohm's law says v is equal to i times r, or voltage is equal to current, which is measured in amps times resistance, which is measured in ohms.

-Limit the flow of electron.

-Resistance is measured in ohms.

-Know how much voltage is used up.

Example 1 : Simple One LED Specs.

Vs : Power Supply 5-Volt circuit.

Vl : LED use 2-Volt.

I : 20mA.

Example 2 : Connecting LEDs in Series.

The power supply must have sufficient voltage to provide about 2V for each LED (4V for blue and white) plus at least another 2V for the resistor. To work out a value for the resistor you must add up all the LED voltages and use this for Vl.

A red, a yellow and a green LED in series need a supply voltage of at least

If the supply voltage VS is 9V and the current I must be 15mA = 0.015A,

Resistor R = (VS - VL) / I = (9 - 6) / 0.015 = 3 / 0.015 =

so choose R = 220ohm (the nearest standard value which is greater).

http://electronicsclub.info/leds.htm

**Understanding Power Flow:**Let start with the basics about voltage, current and resistance. These three components come together in the Ohm's Law, which is the key to understanding a circuit. Ohm's law says v is equal to i times r, or voltage is equal to current, which is measured in amps times resistance, which is measured in ohms.

**Ohm's law:**V = I x R

Voltage(Volts) = Current(amps) x Resistance(ohms).

**Resistors:**-Limit the flow of electron.

-Resistance is measured in ohms.

**Finding the correct Resistor:**-Know how much voltage is used up.

Example 1 : Simple One LED Specs.

Vs : Power Supply 5-Volt circuit.

Vl : LED use 2-Volt.

I : 20mA.

R = (Vs-Vl) / I.So we can use 150 Ohm or higher than,

R = (5-2) / 0.02 A.

R = 3 / 0.2 = 150 Ohm.

__but not less than 150 Ohm.__Example 2 : Connecting LEDs in Series.

The power supply must have sufficient voltage to provide about 2V for each LED (4V for blue and white) plus at least another 2V for the resistor. To work out a value for the resistor you must add up all the LED voltages and use this for Vl.

A red, a yellow and a green LED in series need a supply voltage of at least

**3 × 2V + 2V = 8V, so a 9V**battery would be ideal.**VL = 2V + 2V + 2V = 6V**(the three LED voltages added up).If the supply voltage VS is 9V and the current I must be 15mA = 0.015A,

Resistor R = (VS - VL) / I = (9 - 6) / 0.015 = 3 / 0.015 =

**200ohm**,so choose R = 220ohm (the nearest standard value which is greater).

**Avoid connecting LEDs in parallel!****References :**http://electronicsclub.info/leds.htm

__See The Arduino for Beginners Tutorials__