[Robotgroup] LED's and Resistors?

[Andre Lamothe]

Well, the lights are in parallel feeding off the 4.5V supply, so you can tap 
off that and if you want create a "voltage" divider circuit to generate the 
3V, depending on how many "loads" you put on the voltage divider it will 
change the divider and the voltage will vary, not that important in a simple 
circuit like this, but a concern. Additionally, the ugly part is that it 
will waste power -- Voltage dividers aren't a good way to generate POWER 
SUPPLIES -- they are good for signal control and scaling though--

Instead, here's a trick get (2) 1N4001 diodes -- when they are foward biased 
they will drop about 0.7 volts each, (2) in series will drop 1.4ish volts 
and viola you have your 4.5 - 1.4 = ~3V, no power wasted, and the voltage 
will be very stable over the range of current you pull. So, here's the 
circuit --