DIY_EFI Digest V1 #303

[Heneghan,Paul]

From: "Chaxel Frederic (QUALITE)" <chaxel at cran.u-nancy.fr>
>I get some TOP signals from a captor. This information
>is used to calculate the engine RPM and to calculate the
>Ignition time (by the way of a table).
>But of course I get the RPM at T time and used it for
>ignition at T+DT time (1 engine round after).
>
>My solution is actually to use RPM(T-1) and RPM(T) to calculate 
>RPM(T+1) :
>  RPM(T+1)=RPM(T)-RPM(T-1)+RMP(T)=2*RMP(T)-RPM(T-1)
>
>It's a simple linear approximation (and simple to program
>in assembly language).
>
>This give good results (much more better than using RPM(T+1)=
>RPM(T))
>
>Maybe somebody know a better solution (Kalman Filter
>for instance, or ...) ?

You could try RPM(t+1) = 3 x RPM(t) - 3 x RPM(t-1) + RPM(t-2)
This will work for curves (quadratics only) and straight lines.
If you need higher order (cubics etc.), let me know.
The extra complexity might not be worth it though.

>Sorry for my dirty English !

Looks pretty good to me (you should see my French).

Paul
paul.heneghan at bbc.co.uk