Date: Wed, 26 Dec 2001 02:52:16 -0800
Reply-To: TinkerMan <tinkerman007@YAHOO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: TinkerMan <tinkerman007@YAHOO.COM>
Subject: # tachometer ideas
Content-Type: text/plain; charset=us-ascii
Hello Volks,
The wasserboxer engine system has several RPM related
thresholds, e.g. the ECU is also RPM driven (along
with a whole bunch of other monitored parameters), as
well as the dynamic oil pressure monitoring system
(DOPMS) (which has a built-in 2K RPM threshold.
Moreover, the DOPMS uses a wire coming from the motor
to the dash cluster with RPM data (pulses from the
coil?) for monitoring the engine speed and sounding
the buzzer if low oil pressure occurs above 2K RPM.
This same signal is probably used for the tachometer
if installed.
My 1990 GL doesn't have a tachometer, and I don't want
to replace the instrument cluster as some suggested.
Does anyone know (or has a working solution) of a
simple way to:
1. Monitor some signal in the engine (not so good,
will have to route a wire) or instrument cluster
(prefered) and derive from it RPM data (possibly with
a simple external circuit) for display via a few
simple LED's or for alerting purposes with a buzzer
(e.g. over-revving the motor). I'm not talking about
full blown tachometer, but rather a simple indicator
for some RPM important (e.g. 2K or 5K).
A example of a simple method I could think of would be
to insert a switch in series with the high (0.9 bar)
oil pressure switch. Disconnecting it over 2K rpm
(with the switch) would sound the built-in buzzer of
the DOPMS and serve as a 2K RPM indicator. Now how to
do the same thing without all that noise and no
switch?...;-)
Maybe there are other RPM related signals out there
that could easily monitored with LED's?
2. A simple Tachometer circuit that interfaces with
the standard dash RPM signal. I'd prefer a small,
electronic one with either a LED for each range (e.g.
<1K, 1-2K, 2-3K, 3-4K, 4-5K etc.) or a small LCD
circuit (oops, no! LCD displays might TOAST due to the
heat from the sun on the dash) or LED display. Again,
simple is beautiful...(and also, good things come in
small packages...). Not a large, mechanical one. Maybe
a Frequency-to-Voltage (F->V) circuit that can be used
along with an analog meter (also used with the famous
DIGITOOL ECU analyzer?).
I know it's doable, but why re-invent the wheel? Heck,
I'm sure there's even a cheap kit for this available
(either F->V or direct LED output)?
As far as I've seen, some signal conditioning must be
done on the tach signal as I suspect it's not a low
voltage if it's coming from the coil.
3. Any other interesting ideas on the subject?
**if possible, please send me a copy via p-mail too
since I often miss responses on this very active list.
=====
Cheers,
TinkerMan
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