RE: AD conversions

[Keith Doxey <keith.doxey@xxxxxxx>]

3k @ 15 volts will only draw 5mA and most systems should be able to
tolerate
that especially in the hostile environment of a car. If you are worried
increase the resistor values by a factor of 10.

Using 10k resistors will give 30k which will equate to 0.5mA

Keith


> -----Original Message-----
> From: REB.Barnett@xxxxxxx
> [mailto:REB.Barnett@xxxxxxx]
> Sent: 03 July 2000 14:15
> To: ukha_d@xxxxxxx
> Subject: RE: [ukha_d] AD conversions
>
>
> 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
> > >
> > >
> > >
> > >
> > >
> > >
> > >
--------------------------------------------------------------
> > > ----------
> > > Free, Unlimited Calls Anywhere!
> > > Visit Firetalk.com - click below.
> > > http://click.egroups.com/1/5479/9/_/2065/_/962627412/
> > >
--------------------------------------------------------------
> > > ----------
> > >
> > >
> >
> >
> > --------------------------------------------------------------
> > ----------
> > Win $5000! Click Here:
> > http://click.egroups.com/1/5941/9/_/2065/_/962629195/
> > --------------------------------------------------------------
> > ----------
> >
> >
> >
> >
> >
>
>
>
>
>
> --------------------------------------------------------------
> ----------
> 0% Introductory APR!
> Instant Approval!
> Aria Visa - get yours today.
> http://click.egroups.com/1/6035/9/_/2065/_/962629968/
> --------------------------------------------------------------
> ----------
>
>


------------------------------------------------------------------------
Win $5000! Click Here:
http://click.egroups.com/1/5941/9/_/2065/_/962634132/
------------------------------------------------------------------------