Light up LED

Now that we have discussed the basics of electrical circuits, let's build our first circuit. In this circuit, we will simply light up a LED. We will start off with a look at the schematic diagram, which will tell us how to build the circuit:

In this diagram, we can see that the circuit consists of one 9-volt power source (9-volt battery) one LED and one resistor. One of the first questions people new to circuits ask is how we calculate the value of the resistor. To calculate this value, we need to know what the forward voltage for the LED is and the maximum current it can take without blowing. The forward voltage is the voltage amount required before the LED will conduct electricity and the voltage drop that will occur. If you purchase the LED from a good electronic store, they should have a datasheet that will tell you the forward voltage and the maximum current the LED can take.

We use the forward voltage and maximum current in the following formula to figure out what size resistor we need:

In this formula, the voltage marked with the S is the voltage source, which is 9V in this example. The voltage and current marked with LED is the forward voltage and maximum current, respectively, for the LED. The LED I am using for this example is 3.4 volts and 20 milliamps. This gives a value of (9 - 3.4 volts)/20 milliamps, which are 280 ohms. Since I do not have a resistor with a value of 280 ohms, I rounded it up to the next highest value with is 330 ohms as shown in the schematic.

The following photograph shows how I connected everything:

If you have everything connected correctly the LED will light up when the battery is connected.