Hello! I´m completely new to Arduino, but I need to make my car headlight washers.
My first idea was to take +12V (max +14.7V, car generator voltage) from windscreen washer pump as the input signal. So.. when windscreen washer pump has been active for 3 seconds then another, headlight washer pump, would activate with the help of Arduino and in the sequence: 1.5sec ON - 1.5sec OFF - 1.5sec ON.
How exactly should I do that and what kind of Arduino/relay equipment is necessary?
You don't really need a programmable microcontroller for something like that. You could use an NE555 chip (or something similar). It would be cheaper and you wouldn't need software. But, if you want to use the Arduino you can make a modification of the [u]Blink Example[/u].
My first idea was to take +12V (max +14.7V, car generator voltage) from windscreen washer pump as the input signal.
You could probably just power the Arduino with that voltage rather than using an input and powering the Arduino full-time.
But if you want to use a 12V input, use an [u]over-voltage protection circuit[/u]. (I recommend increasing the current-limiting resistor to between 1K and 10K.)
You can drive the washer pump with a [u]MOSFET driver circuit[/u] or a relay. If you build a MOSFET driver, the MOSFET needs to be rated to handle the pump current (plus some safety margin) and it needs to be a "logic level" MOSFET (which can be controlled with 5V).
A regular electro-mechanical relay also need a driver for the relay coil, but you can buy a relay board with the driver built-in. There are solid state relays that can be directly controlled from the Arduino, but make sure to get one designed to control DC. AC & DC solid state relays are not interchangeale. Again of course, the relay has to be rated to handle the current.
....A solid state relay is the simplest solution.