[Diy_efi] Modify tacho signal.

[Toyota Supra]

hey ian,

i don't know if you are stuck on building something, but here is something 
you can purchase, its relatively cheap

http://www.dakotadigital.com/products.cfm?Category=122

good luck

-j






From: Ian_Haynes at amat.com
>Reply-To: diy_efi at diy-efi.org
>To: diy_efi at diy-efi.org
>Subject: [Diy_efi] Modify tacho signal.
>Date: Sat, 23 Nov 2002 21:39:37 +0000
>
>Hi everyone,
>
>I am new to this list, so go gently with me...
>
>I have a 1990 3 series BMW that originally had a 2.5 litre 6 cylinder
>engine. This has been replaced by a 3.2 litre 6 cylinder engine. Since the
>conversion, the Tach has been reading approx 12% high. Not a big deal, but
>something I would like to correct.
>
>I have looked into the electronics in the Instrument cluster, and all the
>calibration seems to be done with a small 8 pin EEPROM. All the different
>models of 3 series have a different module depending on engine type etc. It
>is not going to be a case of simply changing resistor/capacitor values. The
>EEPROM is labelled as an HML 087. I believe this is some sort of BMW
>special, and cannot find any data on it.
>
>The Tacho signal comes directly from the main engine ECU, and I assume is
>just a frequency that is proportional to RPM. What I want to do, is modify
>this signal before it gets to the Instrument cluster.
>
>Does anyone know if it is possible to make a small circuit that you feed
>the Tach frequency signal in one end, reduce the frequency by approx 12%
>and then send it on its way to the Instrument cluster. Ideally this would
>have some sort of adjustment either by a potentiometer of some DIP
>switches.
>
>Would it be possible to use a frequency to voltage converter, reduce the
>resulting analogue voltage and then use a voltage to frequency convertor ?
>
>All ideas gratefully received.
>
>Many thanks,
>
>Ian Haynes.
>
>
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