Hi Fabio, you might need some filtering to the input pulses for proper measuring. One possible way is to use an RC low-pass filter following with a schimiter trigger. You need to choose the RC parameters according to pulse width and noise frequency. Good luck. Raymond -----Original Message----- From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Fabio Pereira Sent: December 9, 2001 12:14 PM To: PICLIST@MITVMA.MIT.EDU Subject: Re: [PIC]: Digital Tachometer / Rev counter Hello Mark ! > help much. My plan is to use a wire around a spark lead as the sensor with > a PIC counting the pulses and displaying to two 7-seg displays the Revs per I'm in final tests with mine too. It's a digital tachometer with 5 digits and a bargraph of 14 leds, it also has a shift light, revolution limiter, max rpm memory, etc. It's based on 16F872 running at 16Mhz, and it's capable measuring up to 99999 RPM. For more accuracy I'm measuring the period between the Sparks. The tacho, itself it's done, and working OK, but .... Actually, I'm having trouble with the sensor interface .... The EMP from ignition is generating noise and making impossible to measure the period of the Sparks .... BTW.: If someone in the list has any idea for filtering the signal, would be fine. > I'll need some form of transformer to take the 12v car battery to a 5v > regulated circuit for the PIC, any help with all of this would be greatly Why a transformer ???? Why don't you assign a 7805 for the work ??? I think that's no problem using a linear regulator, because the current is very low ... (We are talking about PICs remember !) Thats all ... Let me know if I could help you in any way ... Fabio Pereira Joinville - SC - Brazil -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.