Page 1 of 1

#1 S3 Rev counter

Posted: Sun Sep 13, 2020 10:45 am
by MLBS3V12
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

#2 Re: S3 Rev counter

Posted: Sun Sep 13, 2020 11:27 am
by MarekH
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

#3 Re: S3 Rev counter

Posted: Sun Sep 13, 2020 2:52 pm
by MLBS3V12
Thank you Marek.

#4 Re: S3 Rev counter

Posted: Fri Sep 18, 2020 6:27 pm
by MLBS3V12
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?

#5 Re: S3 Rev counter

Posted: Fri Sep 18, 2020 7:13 pm
by MarekH
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

#6 Re: S3 Rev counter

Posted: Fri Sep 18, 2020 8:07 pm
by MLBS3V12
Yes,
I've already thought to use a 6 cylinder rev counter. there are many ones on Ebay quite cheap.

#7 Re: S3 Rev counter

Posted: Sat Sep 26, 2020 8:28 am
by MLBS3V12
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. 🙂