Tapping existing Tach line

TheArchBish · Post by **TheArchBish** » Sat Jan 31, 2015 7:54 pm

I'm new to this so bear with me. I have an MSD 6AL Ignition Controller and it outputs a tach line - delivers 12V square wave. Can I tap directly in to this for RPM on RCP or do I need some sort of resistor to reduce voltage down to 5V.

gizmodo · Post by **gizmodo** » Mon Feb 02, 2015 2:54 pm

I have an MSD tach adapter that outputs the same signal, a 12 volt square wave. When I asked Brent he said it should be fine since the inputs are protected. I haven't been able to get a signal from it though. Brent did say he ordered a tach adapter to test with, but I haven't heard if he had any luck with it.

TheArchBish · Post by **TheArchBish** » Mon Feb 02, 2015 2:59 pm

Thanks for the info. As its protected I think my best bet might be to take the Tach signal directly from the 12v square wave off the MSD ignition controller. It worked with my old ChaseCam logger. I was just worried about the 12v v 5v mismatch.

Post by **brentp** » Mon Feb 09, 2015 5:21 pm

Hi TheArchBish -

Yes, we ordered the MSD tach adapter recently and we have it on our test bench to evaluate the signal. It wasn't clear to us if it supplies a clean 12v or 5v square wave, so that's why we were curious.

Do you have an MK1 or MK2 RCP? for MK1 the recent 2.7.7 firmware addresses a pretty big RPM bug that people were experiencing; so if you have an MK1 you definitely want to update.

TheArchBish · Post by **TheArchBish** » Mon Feb 09, 2015 5:23 pm

Brent. Mine is a Mk2 with the latest firmware.

Post by **brentp** » Mon Feb 09, 2015 5:33 pm

Go ahead and connect straight to the clean 12v MSD 6AL tach line let us know how it goes. Note, you may have to play with the "pulse per revolution" settings in the firmware to dial in the RPM calibration.

Mattik · Post by **Mattik** » Sat May 07, 2016 10:59 pm

How did it turnout, does it work with tacho signal from Msd to RCP?

We currently instaling Rcp to Drag car trying to sort out how to get rpm signal to RCP.

Will it work with CoilX connected to the Coil as the MSd gives multiple sparks per ignition?

TheArchBish · Post by **TheArchBish** » Sat May 07, 2016 11:53 pm

Yeah worked fine. Only issue I have experienced is if you shut off the engine it tends to "stick" at the last running RPM. However once the engine starts again it all works again.

Post by **brentp** » Tue May 10, 2016 5:32 am

Thank for the update.

Please try updating to 2.9.0 firmware - we fixed the stuck RPM issue as well as introduced a noise filter to help eliminate RPM spikes.

HollyJuster · Post by **HollyJuster** » Wed Jul 06, 2016 4:47 pm

Hi i am new user here and by profession i am a hardware design engineer. I think my best bet might be to take the Tach signal directly from the 12v square wave off the MSD ignition controller. It worked with my old ChaseCam logger. I was just worried about the 12v v 5v mismatch.Go ahead and connect straight to the clean 12v MSD 6AL tach line let us know how it goes. Note, you may have to play with the "pulse per revolution" settings in the firmware to dial in the RPM calibration.

turnkey pcb assembly

viya0414 · Post by **viya0414** » Thu Nov 30, 2017 1:54 am

Only issue I have experienced is if you shut off the engine it tends to "stick" at the last running RPM. However once the engine starts again it all works again.

Post by **brentp** » Thu Nov 30, 2017 1:56 am

Note; the latest firmware release should handle the sticking RPM value if the wire is disconnected.