This is one for the likes of Simon SECS, Stu MSD and anyone else who has in-depth knowlege of the rev counter

How does the standard cosworth rev-counter operate.

From what I gather it has the following connections

VCC
GND
Signal


VCC is battery voltage, GND is self explanitry

It is the signal I am interested in - what sort of signal is it? Is it voltage dependent or frequency dependent?

If it is frequency dependent, what frequency scale does it operate on?


Cheer

 

It sees teh back EMF from the colapsing coil field as far as i understand, and that gives a voltage of around 2 - 300volts per coil trigger.

The tach internals have huge amounts of filtering on to reduce this to a very low level indeed that the tach will operate from, thus if the BMW produces too little volts, the pointer will never even move.

 

I sort of grasp that concept Stu - the BMW tach works on a frequency based system, the frequency which is generated by the ECU

Fuzzy on here with his E30 touring cosworth has the standard BMW revcounter working, but he isn't sure how its been done, as he paid someone else to do it

I need to start looking for ways and means of getting the tacho working, but i'm at a loss as-to where to start

 

i have a circuit schematic for the internals of the Tach if you are really interested Gracey, alternatively If you have a a 12V pulse signal from the ECU it may be quite a simple soldering mod on the tacho to get you working. (asuming you have the same pulse frequency as cossie, ie 2 pulses per rev)
The Ford tacho's are shite, If you look at what happens to the signal internally with the amount of filtering they apply, it's a wonder it ever works at all!! indeed at much over 5500rpm I'm not sure how it does manage to work!

Most of the problems the SECS coildriver has is actually more to do with the tacho's being so crap and variable too, rather than the coildriver system itself..

*EDIT* hmm reading yr post again, I'm not sure which way round you want to do? Do you want to use the BMW tacho (and need to adapt the drive signal) or use the Cossie tacho and get it working with your system?

 

Rich - I need to use the BMW tacho with my cossie engine, L8 ecu with coilpack driver, So I need to interface somehow to get them to talk to each other

Are you on msn chap?