12 V raw, yes, but a charged battery gives around 13 V, and the alternator gives some 14 V, plus there can be some noise spikes even higher. I'd rather not risk burning the chip, so I added a stabilizer circuit. As for the diode, I used the smallest one, it's 0.5 W I believe. With the 1K resistor on the input and assuming 12V signal, the current through the Zener will be 12 mA maximum.
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