Tach Output on MJ

LandyPete · Post by **LandyPete** » Thu Mar 29, 2007 10:42 pm

Two quick questions...

Does the tach out on the MJ unit give a pulse-per-revolution, or a pulse-per-ignition cycle (o.e. 2 per rev for 4 cyl engine)

Whats the voltage on the tach out pin..?

Looking to drive a LM2917 frequency to voltage chip

Cheers

Pete

Post by **brentp** » Thu Mar 29, 2007 10:43 pm

It's pulse per ignition event. It's a 12V square wave.

Regards,

capri_turbo · Post by **capri_turbo** » Fri Mar 30, 2007 7:45 am

2 per rotation on a 4 cyl 4 stroke... that works out at 33.3333Hz at 1000RPM. I have used the LM2917 in the bargraph section of my DIY rev counter and it works spot on with the MJLJ tach output.

More info on my rev counter here:

http://www.ford-capri.fsnet.co.uk/white ... ounter.htm

http://www.ford-capri.fsnet.co.uk/white ... xt_gen.htm

LandyPete · Post by **LandyPete** » Fri Mar 30, 2007 9:14 am

Cheers !

Yours was one of the designs I had seen and wanted to know more about.

Do you drive the circuit straight onto the -ve coil input that you have marked on the circuit diagram..?

I'm looking to run 20 leds, so will be driving 2 IC drivers

Thanks

Peter

capri_turbo · Post by **capri_turbo** » Fri Mar 30, 2007 9:53 am

I was running it before I went MJLJ, so where it says coil LT -ve, wire to MJLJ tach output.

dr.occa · Post by **dr.occa** » Mon Jul 09, 2007 6:59 pm

brentp wrote:It's pulse per ignition event. It's a 12V square wave.

Regards,

sorry, to revive this old thread. will the tach output on the MJ be compatible w/ the stock tach lead on the corolla (4age) or will i have to apply the "high-voltage kick back pulse" suggested in the "How To" section under "Installation"?

Post by **brentp** » Mon Jul 09, 2007 9:54 pm

Use the HV circuit- that's what I have on the MR2. The toyota electronics seems to need this to operate the tach correctly.