DIODES (D) + LIGHT EMITING DIODES (LED)

DIODES (D) are components that allow electric current to flow in only one direction, the direction of the arrow on the schematic. The forward direction is the ANODE (A) and the reverse direction is called the CATHODE (K). They have to be connected the right way around or they clearly wont work, but an actual diode has a line signifying the anode on one end to make this easier.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

LIGHT EMITTING DIODES (LED) are type of diode which emits light when electric current passes through them. They are awesome! There are two wires that hang off every LED, the longer one is the anode and the shorter one is the cathode. Like any diode, they have to be connected in the right direction in order to work. LEDs need to have the correct amount of voltage running through them or they burn out. A standard red LED uses 2.0V and .02mA.

To work out what type of resistor to use in your circuit, use this variation on Ohm's Law:

R = (V_S - V_F) / I

• V_S= Supply Voltage
• V_F= LED Voltage

So if the supply voltage (V_S) is 9V in our circuit, and we are using a single red LED which uses 2V (V_F) and needs 20mA (I) we would need a 350 ohm resistor.

• (9V - 2V) / 0.020A = 7V / 0.020A = 350 ohms

It's better to overestimate resistance rather then underestimate and blow your LED, so use the nearest standard value which is higher. In this case, that would be 390 ohms. Don't forget that resistors have a tolerance value, so use that to fall within the range you need!
.