"Nigel Allen" <(E-Mail Removed)> wrote in message
news:4MmdnSx-(E-Mail Removed)...
<snip>
> Given you know just a little more than the average lurkler here, can you
> take a look at this:
> http://www.instructables.com/id/DIY-...ter-RPM-gauge/
> and tell me if that circuit would work with a twin cylinder machine? I'm
> kind of intrigued.
You mean, I finally get to put my electronics engineering degree to use?
Whoa! 8-P
The circuit'll work with any number of cylinders, because you're not trying
to measure a precise value - merely a calibrated scale of 0%-100%. It's just
a matter of adjusting the trimmer to suit the frequency range given out by
your bike, so even in extreme cases (16 cylinders perhaps?) you'd only need
to change a couple of components to compensate.
There is though one major problem - visibility. If you use standard 8mCD
LEDs, they'll look perfect at night but will be invisible in daylight (even
on an overcast day). If on the other hand you use 500mCD LEDs so you can see
them in daylight, you'll be blinded at night.
You could of course implement a potentiometer or switch and resistors to
manually adjust the current supplied to the display, but that'd be fiddly -
or devise a light-sensitive automatic dimmer, but that'd be more costly.
At a rough estimate of $75-$80 for parts (the semiconductors alone are
nearly $37 from Jaycar) plus several hours of dicking around, I'd have to
ask again, "is it worth it?" Sure it'd be a great adventure in
doing-it-yourself and you'll have no end of self satisfaction when you get
it working, but (1) you'll have much frustration in getting it to work (and
look) the way you want, (2) it won't look professionally done, no matter how
good you are with your hands, and (3) it is only a tachometer after all -
you'll still need to build similar assemblies for the speedometer and fuel
gauge (and potentially battery votage, current monitor, temperature monitor,
etc., etc., etc...).
I'd still go with a ready-made device (especially the $90 from China); given
that it won't look like anything anyone else has on a similar bike, it'll
have enough of the "uniqueness" you seek, and the time you spend connecting
it properly and getting it to mount without falling off at the first corner
will give you the "I did it myself" factor - and it'll have all the extra
facilities, including an odometer and trip meter.
--
Bob Milutinovic
Cognicom