See http://owfs.org/index.php?page=voltage-measurement
You'll need an offset, but many of the "current" sensors measure voltage in
that range.
With a 1.25V offset, the DS2438 would be a great choice. It will measure
+-0.25V with .25mV resolution. The MAX6018
http://www.maxim-ic.com/datasheet/index.mvp/id/3168 can be a 1.25V voltage
reference and cost $1. Probably available as a sample.
>From the list, also look at the T8A
http://www.embeddeddatasystems.com/T8A--8-Channel-12-bit-Analog-1-Wire-Card_p_35.html
although I can't say I've tested it and it calls for "analog support".
If you go this way, I'll ask EDS for data to support the T8A.
Paul Alfille
On Fri, Jul 15, 2011 at 6:39 AM, Pedro Côrte-Real <[email protected]> wrote:
> On Fri, May 27, 2011 at 11:55 AM, Pedro Côrte-Real <[email protected]>
> wrote:
> > The way the system works is it reads temperatures in the panel
> > (outside) and on the top and bottom of the water tank. So for those I
> > would need to use the built in sensors as it would be hard to access
> > the spots to install new sensors. I could however use what you suggest
> > to measure the temperatures of the tubes bringing water to and from
> > the panel.
>
> I've done some more experimentation and this seems to actually be
> pretty easy. The control board has all three sensors continuously
> connected to the same GND and V+. Reading the tension between those
> points with a multimeter gives me a very nicely linear relation
> between the tension I measure and the temperature the control board
> itself shows. All I need now is a 1wire voltage meter.
>
> The only snag is that within the useful range (I've measured 25ºC ~
> 68ªC) the voltage only moves from 1.052V to 1.176V. Does any of the
> onewire sensors have +-0.001V actual precision and not just output? If
> not I'll have to design a PCB with some op amps to expand the range
> for better measurement.
>
> Pedro
>
>
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