arduino in car multiple sensor reading

Hi,

I have a question related the protection of arduino used in car... I want to read multiple sensor like vss, temp etc., the question is how do i protect from voltage spikes? Do i need to put protection only on arduino supply or also on analog sensors? Sorry if sounds stupid... but i really dont know how to proceed.

Thanks in advance.

More important is the analog sensors, the power already runs through a 7805 (or similar) regulator if powered externally.

I had a similar issue in a project before.

depending on how big the spikes are, you can use resistors in series (voltage dividers) to scale the voltages down. I use variable trimmer pots in series so you can adjust it just right. You would need 2 voltage dividers (4 resistors). The first would make 12V -> 6V, and the second would change the 6V -> 3V. so with the dividers in place you can read any voltage that does not exceed 20V. Even that is cutting it close. I hope this is what you are looking for as most auto sensors are based on 0 -> 14.5V Max.

regarding this manner you have to select a higher range resistance for the resistors so the current draw from the divider doesnt offset the sensor output voltage. I would try anything between 5k to 50k at first. probably 10k is a good start.