I am making a game, and need 6 resistors for some leds. All of the leds are 20 mA. The circuits are shown below. Can anyone tell me what resistors I need? Can you also direct me to a web page where I can find a resistor calculator that will tell me what resistors I need in the future?
Thank you,
Jason

Circuit 1)
_____________________________________________________
| | | | | | |
| 1.85 volt 1.85 volt 1.85 volt 1.85 volt 1.85 volt 1.85 volt
| led led led led led led
| |_________|_______| |________|_______|
| | |
9 volt Resistor 1 Resistor 2
battery |_________________________|
| |
second |
9 volt |
battery |
|___________________________ |

Circuit 2)
_____________________________________________________
| | | | | | |
| 2.0 volt 2.0 volt 2.0 volt 2.0 volt 2.0 volt 2.0 volt
| led led led led led led
| |_________|_______| |________|_______|
| | |
9 volt Resistor 3 Resistor 4
battery |_________________________|
| |
second |
9 volt |
battery |
|___________________________ |

Circuit 3)
_____________________________________________________
| | | | | | |
| 2.2 volt 2.2 volt 2.2 volt 2.2 volt 2.2 volt 2.2 volt
| led led led led led led
| |_________|_______| |________|_______|
| | |
9 volt Resistor 5 Resistor 6
battery |_________________________|
| |
second |
9 volt |
battery |
|___________________________ |

 

Let me refer you to this part of the E-book -
Volume III - Semiconductors » DIODES AND RECTIFIERS » Special-purpose diodes.

The section on LED's should answer your questions. You also might want to refer to Volume 1 and how to work with series/paralled DC circuits.

The formula for you calculations is: R = E/I, where R is resistance, E is voltage and I is current.