I have no person that I can discuss this problems...
1. I'm planning to use NXP LPC2478 processor for RPM counter. It has 32 bit timer and hardware allowed to fill up to 4 MHZ fill signal. So I can use 555 timer to form proper signal from Hall sensor. I can easy take care about 5 microsecond open gate ... But I come up the Arduino device and decided to switch to it . Many reasons for that .. free developer tools and a lot of sensors and shields...
I have short conversation with guy that deal with dynamometer and he measure RPM using extra Hall sensor for crankshaft teeth.
It has 32 Teeth ( I will measure tommorow), so I can get more accuracy measurement of RPM.
Some people advise me that I can measure acceleration and find out how cylinder 1 and cylinder 2 works using measure the period between teeth.
Arduino use 12V for main power from power supply. To USB port just hookup +5V backup battery. So wheck when power down Arduino still working without interuption. Work fine. But how to find out in my program when 12V lost (220V down)?
I know I can use any pin hookup to 12V( using resitors) and messure, but may be more easy way to do that ?
I hope it should be like Interupt that happend when Arduino switch from one power to backup and back