12V to 5V

Using Arduino Project Guidance
2

How much 5V current do you need? If it's less than 3A, there are many 5V linear regulators to choose from. Mouser lists dozens.
Here's a likely one, an ST Microelectronics LD1085V50ST

http://ca.mouser.com/ProductDetail/STMicroelectronics/LD1085V50/?qs=sGAEpiMZZMsGz1a6aV8DcCRy2MVkeVbmq8UhGP29P1g%3D