So far, that a novice in this area, do not blame me. Make a "tachometer" for the car.
On the arduino you plan to feed al. current with high frequency (approximately 4 signal one turn dvigatelem and up to 8,000 rpm*, i.e. somewhere 533 signals per second).
First wrote a function that ate all the CPU time and checked each step of the signal status on the digital port and add 1 to the counter if the signal was varied from 0 to 1.
Just a couple of minutes ago came across the function attachInterrupt, rewrote everything with it and everything seems to work great. But the problem lies elsewhere.1.
Since in the car walks current 12 volt had to make a "Converter" from 12 to 5 volts. Once I figure out how to do it right, necessarily come off their hands, but now it's 15 simple diodes and 1 transistor. It turned out 4.8 volts at the output, which is quite suit me, but such an abundance of the diodes I have a problem and asking for your help, as all correctly to organize?2.
For tests (and not to burn the computer) from an old phone charger and half a usb cable for arduino made Board (connected the 2 wires, + and -). It worked, but when connect from charging, the arduino at all does not see a signal on the pin. If you turn back to the computer, then everything works fine and the signal it recognizes. Just read again the documentation on the Arduino and noticed a note "author External power (not USB) can be supplied via an AC/DC (power supply)", i.e. he meant that it is impossible to supply power not from the computer to the usb port?You know, a seasoned "techie" would long ago have taken this poor Arduino and put in a corner, but I just started to learn it and I hope for your help)