Digital Tach

[Bernd Felsche]

Lachlan tapped away at the keyboard with:

> I am an advocate of simplicity and would prob not go so far as a
> PLC or other programable device. Apart from the fact that I only
> ever did it at TAFE in Aus and would have to 'learn' it all over
> again!. I think that with simple components like counters and
> dividers and common logic IC's you could easily do this but having
> said all that I would probably end up building a multi-function
> device that had bar graph, digital display and a switch to switch

Two important questions:
How accurate does the RPM have to be (resolution and time-base)?
How frequently do you want the display to update?

The greater the "quality" of the instrument, the greater the
functional complexity.

Would it be sufficient to display the count of ignition pulses over
five 6ths of a second as hundreds of rpm? That's about the simplest
digital (counter-timer) implementation. Need faster response or
higher resolution? Then it gets more complex.

With the cost of microcontrollers quite low, you quickly arrive at
the point where it's chepaer to make it a hardware/software
combination; not quite single-chip implementation, but pretty close.
You also get the benefit of flexibility; i.e. adding on data
logging, etc without re-designing the whole instrument from scratch;
especially if you can think ahead a little and not box yourself in
with the first implementation.

> Lachlan. (ranting)
> 


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