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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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