RE: AD conversions

[REB.Barnett@xxxxxxx]

Cheers Nigel and Keith!

Do I need to worry about the fact I'm effectively connecting the output
from
the ECU to ground via 3 1k resistors? If I connect directly from the ECU to
the ADC (for the 5v signals) then I'm presumably Ok because the ADC has a
high impedance(?), but does 3kohm count as high impedance and hence safe?

Ray.

> -----Original Message-----
> From: Keith Doxey [mailto:keith.doxey@xxxxxxx]
> Sent: 03 July 2000 13:51
> To: ukha_d
> Subject: RE: [ukha_d] AD conversions
>
>
> Hi Ray,
>
> You need to allow upto 15 volts as a car with a fully charged
> battery will
> be about 14.4 volts.
>
> Simply add a voltage divider to tap of the required voltage.
> Your source
> signal is 0-15v you need 0-5v for the converter so you need
> to reduce it to
> a third of what it was.
>
> dodgy calculations follow as they are affected by the source
> impedance of
> the driving signal and the input impedance of the A/D
> converter but in most
> cases....source impeadance will be low, A/D input impedance
> will be high so
> can be fairly safely ignored.
>
> Simplest voltage divider is 3 x 1kohm resistors in series.
> Connect one end
> to source and the other end to ground. Connect the A/D
> converter to the
> junction of the 2 lower resistors in the chain i.e. the
> grounded end. That
> will give you a 0-5v range. If you get the wrong one you will
> get 0-10v.
>
> HTH
>
> Keith
>
> > -----Original Message-----
> > From: REB.Barnett@xxxxxxx
> > [mailto:REB.Barnett@xxxxxxx]
> > Sent: 03 July 2000 13:33
> > To: ukha_d@xxxxxxx
> > Subject: [ukha_d] AD conversions
> >
> >
> > A slightly off topic question, but an answer or pointer to a more
> > appropriate forum would be appreciated!
> >
> > I've now worked out the required bits to add a data logger
> to my car.
> > However, the AD converter accepts an input between 0 and 5v,
> > whereas some of
> > the outputs I want to capture run up to 12v. How do I
> > increase the range of
> > the AD converter? Can I simply whack a resistor in line with
> > the input, or
> > should I do something more sophisticated with an opamp or
> > other gadget?
> >
> > Cheers,
> >
> > Ray Barnett
> >
> >
> >
> >
> >
> >
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