Hi,

If anyone would like to see the code and the schematic, mail me and I'll
mail it to you.

Regards,
Niki

> I think you project is neat!
> Would you be willing to share your code (just for personal
> non-commercial use).
> tks
>
> Mike Montaigne
> montaignem@aecl.ca
>
> >----------
> >From:  N STEENKAMP [M.ING E&E][SMTP:STEENKMP@FIRGA.SUN.AC.ZA]
> >Sent:  Tuesday, January 13, 1998 4:58 AM
> >To:    PICLIST@MITVMA.MIT.EDU
> >Subject:       Re: pic tachometer...
> >
> >Hi,
> >
> >> Once again I'm drawing upon the infinite wisdom of the PICLIST...
> >>
> >>   I'm building a simple pic-based automotive tachometer and would like
> >> to count pulses from the primary lead of the ignition coil and display
> >> the RPM on an LCD.  For peace-of-mind (and other reasons), I'd like to
> >> isolate the input pin of the pic with a 4N35 optoisolator.  I can handle
> >> everything but the connection to the coil...
> >>
> >> I have 2 questions -
> >>
> >> 1.  What is the maximum frequency that the 4N35 will reliably switch at
> >> (will it keep up with the pulse train from the coil)?
> >>
> >> 2.  What do I need to do at the optoisolator's input to handle the
> >> ignition pulses?
> >>
> >Just a comment:
> >I have also constructed an automotive tachometer about a year ago.  I
> >have found that counting pulses in a fixed period is not a very good
> >approach, since the frequency of pulses can be quite low.  At 600 RPM it
> >is 20Hz for a 4cyl engine.  That means that your counting period must be
> >quite long to be able to get sufficient accuracy, which means a
> >slow update rate of the display.  The method I used was to time the
> >period between two pulses and calculate the RPM from that.  I
> >wanted to keep the refresh rate between 5 and 10 times per second.  Since
> >the higher the RPM's the shorter the period, I was also able to average
> >samples at higher RPM's for a stabler display.  From 0 to 1200RPM's I
> >used 1 sample, from 1200 to 2400 I used 2 samples.  From 2400 to 4800 I
> >used 4 samples and from 4800 upwards I used 8 samples.
> >
> >The project uses a 16C54 running at 20MHz and the display is a 16x2 LCD.
> >It has a resolution of 10RPM's.  In the top line of the LCD I display the
> >RPM's in digits and in the bottom line I have a bargraph display (made by
> >using the programmable characters of the LCD).  The display is
> >really fast and responsive.
> >I guess that using one of the PIC's with a capture and compare unit
> >would have been easier, but I wanted to see what I could do with a 54!
> >
> >Regards,
> >Niki
> >
>