Protecting Arduino from car voltage?

[tommydog]

I am using an ATtiny85 to detect voltage on the analogue pin from an ignition live in a car.  It is wired up via a piggyback fuse from the cars fuse box.  When the ATtiny85 detects a voltage from the ignition live it turns an LED on.  This all works perfectly, and all I am using is this connected directly to the ATtiny85:

Arduino 25v DC Input Voltage Sensor Module Tester Board DC001
https://www.ebay.co.uk/itm/Arduino-25v-DC-Input-Voltage-Sensor-Module-Tester-Board-DC001/223529777639?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

The problem is I have read various forum posts of people saying that voltage regulators are needed to avoid frying the Arduino. The thing is, my setup seems pretty stable.  I have checked everything with a volt meter while reving the engine etc and seem to get a pretty constant 12v.  So should I really bother with a regulator etc?  This would involve added work / complexity, so if it's not needed I would rather not use it.  What are peoples opinions on this?

[DVDdoug]

I've got an Arduino running in a vehicle (for a couple of years) and I'm just using the Arduino's built-in regulator.

I have checked everything with a volt meter while reving the engine etc and seem to get a pretty constant 12v.

It's supposed to be about 14.4V when charging, but the "issue" is potential short-term spikes that your meter won't show.

[SteveMann]

The ATtiny85 uses the MC78M05B regulator. The MC78M05B Data Sheet rates the input voltage of 5-18V.

[gilshultz]

You are correct in assuming you need protection.  NOTE: Load-dump protection devices protect sensitive semiconductors in electronic modules used for battery charging against load-dump surges which are caused when a discharged battery is disconnected from the alternator while the alternator is generating current. There is also the 24 Volt double battery jump and assume it will be connected backwards.
For me the simplest solution would be to replace the regulator.  You can search for"load dump protected regulator" you will find out there are many.
Good Luck and Have Fun!
Gil