Volt/Amp protection

Hi guys ... I've started with Arduino some months ago and a friend of mine asked me to build a rpm counter....

I've been looking for internet and I've found some tutos like those ....


But the question is... how should I protect the board from coil volt/amp in order not to burn the Arduino??

I'm thinking about a 5v regulator... but It will be enought not to overamp?


You could try calculating the current first.


You can protect the Arduino's inputs from over voltage with a pair of "protection diodes" and a resistor as show on the 2nd schematic [u]here[/u]. (I recommend changing the resistor to between 1K and 10K.) Or, you can combine that with a [u]voltage divider[/u].

The Arduino board has an on-board voltage regulator and it will run directly from 12V as long as you don't try to power too many additional things from the same regulator. (That's for the power supply, not the signal-input pins.)

The current (Amps) depends on the load (and the applied voltage... [u]Ohm's Law[/u]). For example, although a car battery can supply 500 Amps or so for starting the car, if you connect a regular 20mA LED with the appropriate current limiting resistor, you'll get 20mA through the LED & resistor.

The Arduino's output pins are rated for 40mA maximum at each pin and 200mA total combined. So you can power LEDs or drive an LCD display, but if you need more power/current you'll need a transistor, MOSFET, or relay, etc., to "boost" the current and/or voltage.