S3 Rev counter

Technical advice Q&A
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MLBS3V12
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#1 S3 Rev counter

Post by MLBS3V12 » Sun Sep 13, 2020 10:45 am

Hi,
I've an XJS engine with the Marelli ignition.
The signal coming from one of the amplifier goes through a 6.8Kohm to the XJS counter.
Can I plug directly this signal without any resistor to the input from the S3 Rev counter ?
Thanks for your return
Le chemin sera long!...

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MarekH
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#2 Re: S3 Rev counter

Post by MarekH » Sun Sep 13, 2020 11:27 am

Yes.

Mine operates from a simple 12v square wave signal from the Megasquirt.

The s3 tacho has a 4k3 resistor to earth and a 4k7 resistor on its input into the chip that interfaces with the tacho needle, so it looks to me like that is a potential divider which drops its coil signal down to about 5v anyway.

Make sure it is earthed properly, as that is its weakest link.

kind regards
Marek

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#3 Re: S3 Rev counter

Post by MLBS3V12 » Sun Sep 13, 2020 2:52 pm

Thank you Marek.
Le chemin sera long!...

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#4 Re: S3 Rev counter

Post by MLBS3V12 » Fri Sep 18, 2020 6:27 pm

I've done a test and I confirm that the signal I was talking about allows the rev counter to run.
However, because it comes from one half V12, it counts only half of the turns!
There is one wire coming from the second amplifier.
I do have to use the 2 signals. How can I do that ?
Do I've simply to use 2 diodes, one on each wire?
Le chemin sera long!...

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#5 Re: S3 Rev counter

Post by MarekH » Fri Sep 18, 2020 7:13 pm

Yes, if you have a second amplifier for the other bank, otherwise just use a 6 cylinder tacho instead a 12 cylinder tacho.

kind regards
Marek

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#6 Re: S3 Rev counter

Post by MLBS3V12 » Fri Sep 18, 2020 8:07 pm

Yes,
I've already thought to use a 6 cylinder rev counter. there are many ones on Ebay quite cheap.
Le chemin sera long!...

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#7 Re: S3 Rev counter

Post by MLBS3V12 » Sat Sep 26, 2020 8:28 am

I m going to use a 6 cylinder rev counter....
I ve found one with a clock. Even if I ve already one on the dash board. I found it nice. 🙂
Le chemin sera long!...

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