[Diy_efi] coil (-) tach signal conditioning

[Dennis Noordsij]

On Monday 03 March 2003 19:55, Tomas Sokorai Sch. wrote:
> Hi!
>
> I'm trying to get a clean 5V square signal from the (-) terminal of an old
> Ford Duraspark electronic ignition for a display/datalogging circuit I'm
> building (PIC16F877A w/ hd44780 LCD, GPL'ed; PC datalogging & prog. tools
> software for Linux. I'll release the first ver. it when it's doing
> something useful :)

Hey cool!

I am using the 877 for an EFI controller. Very similar to Megasquirt, but with 
the benefit of hindsight :-) and of course a based around a PIC instead. 
And yes Linux based tuning software of course!


> I tried with the tach input stage from the Megasquirt circuit, and tried
> the tips for tuning this part of the circuit, but I'm still having
> problems. 

I found a different circuit for the Tach input, which you can see at 
http://www.bubblesoftonline.com/projects/points.html

Note that it looks good (with the transistor ground being digital ground, but 
the diodes etc being a tach ground which is completely seperated from the 
other grounds and routed to the engine block seperately, and some zeners and 
a resistor to protect the PIC interrupt line) - but that I haven't tried it 
in practice yet :-)

If you do try it, please do let me know how it turns out! I only intend to use 
it with electronic ignitions, not points. 

Goodluck with the project!
Cheers,
Dennis