On Fri, Jul 15, 2011 at 12:40 PM, Paul Alfille <[email protected]> wrote: > 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.
This one does have plenty of resolution and would be a great fit. I'd have to cook up a small pcb but that should be doable. > From the list, also look at the > T8A http://www.embeddeddatasystems.com/T8A--8-Channel-12-bit-Analog-1-Wire-Card_p_35.html This one is just barely at the level I wanted with 0.00122V resolution over 0-5V. And I wonder if this is real resolution? 5V/2^12 = 0.001220703 so they're basically quoting me the number of steps from 0-5V. I wonder if the actual measurement has that quality of if the low order bits will just be noise. Basically in the final output: 12 bits -> +-0.43ºC 11 bits -> +-0.86ºC 10 bits -> +-1.71ºC So getting the full 12 bits would seem important. Any idea of how good it actually is? Realistically I can get by even with +-2ºC for the kind of decisions I'll be taking with the data (e.g., turn on the electric heater if the water goes below 30ºC and the solar panel is cold) but I'd love to get the better data if I can. On another note the impedance seems pretty good at 100KOhm, basically being 100:1 to the sensor. I get an almost 0.5ºC reduction in the reading in the system when I connect my crappy multimeter. > 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. What is "analog support"? I'd be happy to help support this and can make parallel measurements for calibration. It looks interesting for a bunch of possible applications. It is a bit pricey though compared to the 8 I/O from hobby boards that also includes 8 relays. I haven't been able to find any resolution data on that one though, it's probably much worse. Pedro ------------------------------------------------------------------------------ AppSumo Presents a FREE Video for the SourceForge Community by Eric Ries, the creator of the Lean Startup Methodology on "Lean Startup Secrets Revealed." This video shows you how to validate your ideas, optimize your ideas and identify your business strategy. http://p.sf.net/sfu/appsumosfdev2dev _______________________________________________ Owfs-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/owfs-developers
