Solid state voltage divider for ADC
Archiver
Posts: 46,084
Is it possible to create a solid state voltage divider? as opposed to a
resistor cicuit. The ADC max voltage is 4.096v and I would like to read a
voltage of 15vdc max.
thanx
Matthew
resistor cicuit. The ADC max voltage is 4.096v and I would like to read a
voltage of 15vdc max.
thanx
Matthew
Comments
take it you mean "active" (after all, resistors are solid :-) ). Any
amplifier with a gain<1 would act like a voltage divider.
However, what's wrong with a resistive divider? If you don't want it loading
your source, you could put a 1x buffer amplifier in front of the divider.
The amplifier's "division" will be no better than the gain setting
resistors, so you aren't really better off there. Plus you get offset error,
etc. If you can't get standard resistors to give you the right ratio, you
won't have any better luck with gain-setting resistors, I imagine. If you
use a pot, it will be just as inaccurate at setting gain as it would be as a
divider (not that it will be so bad, just no better one way or another).
So the short answer is use an op amp amplifier with gain<1, but the long
answer is are you sure that's what you want?
Regards,
Al Williams
AWC
* 8 channels of PWM: http://www.al-williams.com/awce/pak5.htm
>
Original Message
> From: Matthew Lewis [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=rcSL2SUVm3oecIR9UxZ-46m1vEMqIvER2wY1lfeZ_OUaG-Z4QE3ebwNsquS83ycuEM-6QbwLnB4SOQjekiw]aiden.bell@h...[/url
> Sent: Friday, August 04, 2000 12:29 PM
> To: basicstamps@egroups.com
> Subject: [noparse][[/noparse]basicstamps] Solid state voltage divider for ADC
>
>
> Is it possible to create a solid state voltage divider? as opposed to a
> resistor cicuit. The ADC max voltage is 4.096v and I would like to read a
> voltage of 15vdc max.
>
> thanx
>
> Matthew
>
>
>
the stability of the resistor cicuit. It seems to have a +- 30mv range. I
guess I really want to retain as much acuracy as possible in the circuit.
Original Message
From: "Al Williams" <alw@a...>
To: <basicstamps@egroups.com>
Sent: Friday, August 04, 2000 10:54 AM
Subject: RE: [noparse][[/noparse]basicstamps] Solid state voltage divider for ADC
> I'm not sure I understand the thrust of your question. By solid state, I
> take it you mean "active" (after all, resistors are solid :-) ). Any
> amplifier with a gain<1 would act like a voltage divider.
>
> However, what's wrong with a resistive divider? If you don't want it
loading
> your source, you could put a 1x buffer amplifier in front of the divider.
>
> The amplifier's "division" will be no better than the gain setting
> resistors, so you aren't really better off there. Plus you get offset
error,
> etc. If you can't get standard resistors to give you the right ratio, you
> won't have any better luck with gain-setting resistors, I imagine. If you
> use a pot, it will be just as inaccurate at setting gain as it would be as
a
> divider (not that it will be so bad, just no better one way or another).
>
> So the short answer is use an op amp amplifier with gain<1, but the long
> answer is are you sure that's what you want?
> Regards,
>
> Al Williams
> AWC
> * 8 channels of PWM: http://www.al-williams.com/awce/pak5.htm
>
>
>
> >
Original Message
> > From: Matthew Lewis [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=EgNKDPG8s-wPgavLNVc3GxCencJZmiVVqBoswob2TU4IdfR_LCJhuB2nlYyZoYRHBjS6QNWZlCLf8w]aiden.bell@h...[/url
> > Sent: Friday, August 04, 2000 12:29 PM
> > To: basicstamps@egroups.com
> > Subject: [noparse][[/noparse]basicstamps] Solid state voltage divider for ADC
> >
> >
> > Is it possible to create a solid state voltage divider? as opposed to a
> > resistor cicuit. The ADC max voltage is 4.096v and I would like to read
a
> > voltage of 15vdc max.
> >
> > thanx
> >
> > Matthew
> >
> >
> >
>
>
>
>
>
>I do mean active [noparse]:)[/noparse]. I have tried the buffer idea but my concern is with
>the stability of the resistor cicuit. It seems to have a +- 30mv range. I
>guess I really want to retain as much acuracy as possible in the circuit.
Is it varying +- 30mv with temperature variations? This swing is unlikely
to be the voltage divider, but you may want a smoothing function on the ADC
output. Are you taking a bunch of samples and then averaging them? A 12 bit
ADC output could flutuate this much just due to noise...
Cheers, Duncan