Using LED(Light Emitting Diode)

LED is one of the most efficient device. It is a semiconductor device like diode which emits light. It also has the diode characteristic, as a rectifier. it can emit fair amount of light with small amount of electrical current.unit of light is usually being represented with lumen. The comparison of electrical power consumed and lumens produced is among the highest of many kinds of lamp.

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LED needs about 20 mA current and 0,7 voltage drop. To drive the 20mA  current, you will need a resistor to limit the current based on the supply voltage.

There are 2 legs, the cathode and anode. anode is the positive polarity and cathode is the negative polarity. Electrical current can only flow from anode to cathode. The difference from diode is the light emitting and current limit. LED can’t pass large amount of current, only about 25-30mA max. Anode is usually the long pin in LED, while the cathode is the shorter one. another way to identify the pin is by looking for the flat side on the LED. the pin on flat side is the cathode.

Here are some example for driving a led with a resistor.

Assuming that you use 5V supply, there will be a 0,7 voltage drop on  a LED, thus the voltage in resistor will be about 4,3 V.  If you the  use two LEDs, the voltage drop will be 1,4 V and so on. To drive the 20mA current, we will use the formula from ohm’s law.

V=I*R              –>             I=V/R

So, to drive 20 mA on the circuit, the value of R1 should be 4,3/20m = 215 ohm. You will find  the value 220 ohm in market, the closest value.

review of step to drive a LED:

– count the voltage drop of all LED used.

– count the voltage on resistor

– count the resistor value needed with ohm’s law

– find the closest value on market

*picture taken from google