5V to 12V

What is the simplest/easiest way to bump 5 volts to 12 volts?

a 5V to 12V DC-DC Step-Up Converter.
Like: http://www.circuit-projects.com/cimg/usb-5v-to-12v-step-up-dc-dc-converter-by-lt1618.gif

N314:
What is the simplest/easiest way to bump 5 volts to 12 volts?

What are you trying to do? if you need to power a 12V device, there are DC to DC converters. If you are adjust signals, op-amps might be option.

I am trying to give a wireless transmitter more power, it takes up to 12 volts, but my Arduino only supplies 5.

In that case a DC to DC convertor will not meet your needs since the power out of DC to DC convertor is less than the power input and the Arduino power output is extremely limited.

Are you trying to increase the signal to the modulation input to the transmitter or are you trying to increase the power line (Vcc) of the transmitter.

N314:
What is the simplest/easiest way to bump 5 volts to 12 volts?

You need to use a separate 12 volt supply. Tie the Arduino ground to the 12 ground and the transmitter ground then tie the +12V to the transmitter. If you're trying for battery operation you can use a 12volt battery with enough milliamp hours and use it to power the arduino and transmitter.

If you are running off of USB and need 12V, here is what I do. I use a TL497A. (an older but useful regulator IC… I bought a bunch years ago) These are still available from Mouser for around $2.00 each and sample designs are real easy to find and are cheaper than MAXIM PWM step up controllers. (Max733, max618, etc)

Another good chip is the MC34063.

Both chips will need a power choke (coil) to create the step-up voltage but that is the only oddball component needed.

http://www.micro.feld.cvut.cz/home/XE34NZE/prednasky/08%20SS-control%20circuits.pdf