[Diy_efi] coil (-) tach signal conditioning

Joseph Obernberger joelori at earthlink.net
Wed Mar 5 06:00:17 GMT 2003


Hi - neat project idea!  You may want to look at national semiconductor's LM1815N
chip.  It works very well at signal conditioning reluctor signals.
http://www.national.com/pf/LM/LM1815.html

                                            joeo

Homepage:  http://cybrina.mine.nu

"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 :)
> 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.
> If the capacitor values on the coil side are normal (like the one on the MS
> circuit), the tach signal is sometimes "doubled" or it's timing jumps too
> much. But with a big enough capacitor values to get a steady and real value
> for idle, it doesn't want to "go up" with RPM.
> In the software the time between 4 pulses is 50% "lag filtered" (as described
> in the GM_ECM paper) to do the RPM calc. I'm sure the software is working OK,
> tested with a clock generator circuit (a megaexpensive one... a 555 ;), and
> always get a steady and get a very near to the theoretical RPM value for the
> calculated RPM.
>
> Ideas for another (-) coil input? or does the Duraspark 1 have a particularily
> brain-damaged waveform?
>
> Thanks in advance
>
> --
> Tomas J. Sokorai Sch.
>
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> Diy_efi at diy-efi.org
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