555 EFI again...

[Walter Petermann]

> > > >http://brokersys.com/~corsaro/wiring_diagrams/555fe.htm
> ...
> ... The voltage across
> > > the capacitor rises in an exponential fashion, whereas we require that
> > > the voltage rises in a linear ramp.  This can be acheived by using a
> > > constant current source to charge the cap.
> ..
> > > Chris Morriss
> 
> Clare Snyder wrote:
> > How do we implement this - modification to the referenced circuit?
> 

I wanted to see just how bad the effect of the non linear RC charging
was...It's BAD. Over 25% error at atmospheric pressure ( reference input
at max = 2/3*5v). I made a plot of the response and added it to the page. 
I have a current circuit in mind..someone sugested a current mirror. 
I'll try that and not use the extra op-amp. 
 
 Walter