[Diy_efi] I need to rectify a low ac voltage.

[Jörgen Karlsson]

Bernd Felsche wrote:

> How about biasing the cell by 500mV in one direction? You probably
> have a floating ground already. That would eliminate the
> rectification requirement.

That won't help much, I would need to sample the signal to find the highest
reading and I can just as well do that with the signal referenced to ground.

> I don't know why you'd want to filter the signal externally if
> you're using a uC. It doesn't change that quickly. The ADC will
> latch onto the signal at the start of conversion and will maintain
> that sample voltage until you initiate the next one. If you sample
> frequently, then you can also filter digitally to remove glitches,
> etc..

I have thought about it and I think it is the best idea. The rectification
will help here too. But it would be nice if I didn't need to think about
that when I write the code.

The original idea was to read the impendance of the sense cell by applying
an ac voltage, that is the way bosch want it. But by measuring the
impencance of the pump cell instead I have been able to remove several
components. The rectifier helped a lot here too as I always have a valid
impendance signal on one of the adc inputs.

You can take a look at the schematic at
http://www7.brinkster.com/jurgmannen/mdwb/md.htm.
I forgot to implement the filter on that schematic and it needs a few other
changes but it is a start. The current board size is 80X100mm and the
components can be packet to get a 80X55mm board but I think that I will use
the rest of the board space to add alternative building blocks. This is a
prototype after all.

Jörgen





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