Here is a great and very simple circuit for beginners in electronics that lights a LED lamp!
All you need is a LED,a battery and a resistor
If you don't know which LED leg is positive and which is negative there is a very easy way to find out.
Look into the LED bulb-the big lead is negative (Ground) .Ground connection always have to be bigger.Many problems arise in circuits because of bad grounding.
Here is a blow-up of a LED head.
 |
| the big lead is negative |
Some science
Now let's go into some more detail.You need a resistor to light the LED and to protect it from excessive current.
resistor value
How to calculate the resistor value.
Simple.Using Ohm's Law V=IR or R=V/I.
An extended form would be R=V1-V2/I.
or resistance=sourceVoltage -LEDvoltage/LEDcurrent
Red LEDs have about 2 volts and their forward current is 15 miliAmperes or 0.015 Amperes.Other LED colors are rated different.
The battery we use here is 9 Volts.
So ,replacing the formula for these values we get
R=9V-2V/0.015=466.66667 or 467 ohms for the resistor.If you cannot find a resistor of the exact value then pick one with the next closest value.It will do.
resistor Wattage
Now we need the resistor Wattage.
ResistorWattage=sourceVoltage -LEDvoltage x LEDcurrent
R=9V-2Vx0.015=0.105 which means that 1/4 watt resistor will do.
Resistors come in various wattages 1/4, 1/, 1/2,1 watt,2,5,etc...
calculator
If you still cannot get it try this online Ohm's Law resistor calculator.
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