I am building a circuit that would connect inputs between 12 to 24vdc to an arduino mega. I would normally accomplish this using a resister and zener diode. However, using a resister and zener diode will draw too much current because I have about 30 inputs. Each zener needs about 50ma of current draw to keep it in the 5v area. 30 x 50ma 1.5amps. Therefore, I need a circuit that would provide 5v to an arduino input from a 12 to 24 supply with very minimal current draw. Any ideas?

 

Standard off the shelf automotive power port to USB adapter. Most are rated for 12 - 24 VDC input and can supply around 2 amps on the better ones.

Might cost you up to $8 for a high quality one though.