I will be building some small Arduino and ATtiny85s systems for vehicles and would like a suggestion on the best way to power them from a 12-14vDC source. Could I use a simple DC-DC converter (like a VB1205S-1W), or would it be prudent to use something more complex to protect the processors from the starter/ignition system? All the other components in my circuit (relays etc) will run off the 12v source, so I don’t need much more 5v current beyond what the processors will require. Thank you for any guidance you can provide…
If excess heat isn’t a problem, a cheap and simple 3 terminal 7805 would work. In any case, overvoltage protection is smart.
I am running one in the car with a regulated 12 V to 5 Volt converter. If the car is not that old, the starter or generator will not cause to much ‘dirt’. If Cars have docking stations for Ipod etc, the manufacturer usually had to put in voltage filters in the first place.
I’d recommend Murata’s OKI-78SR product range ($4 at mouser, 7-36VIN range, output at 3.3 or 5 depending on the part, 1.5A out. Pretty much a switching regulator drop-in-replacement for the 7805 that costs about 8x as much for well over 2x the energy efficiency). As a general circuit:
Have a diode on the battery line going in, a decently-sized cap between that wire and ground after the diode, then the VIN pin on that wire. Have the cap be big enough that it can handle the power requirements for your circuit for a couple of seconds (that way if the battery drops below ~7V while starting, which is unlikely, but depending on your application worthy of consideration, esp for the extra buck or two the extra hardware will cost you, the cap will still be able to power the circuit)