Still undecided. I got dragged off onto some other work, although I should be able to devote some more time to this in the near future. The initial probe I threw together just to get some data was a simple 2-wire probe that measures voltage drop across them, so, yeah, continuous DC. It worked as a simple tool. The electrolysis would be greatly helped by pulsing the power briefly to take a periodic measurement. Of course, setting up AC would also help. A capacitive measurement would also be good, but I haven't come up with a simple circuit and probe for that...one of the capacitive touch sensors (a la iPod) might work. -Pete On Aug 17, 2008, at 9:12 AM, Grif w. keith griffith wrote: > > What kind of sensor did you end up pic'ing? (bad pun) > > > At 08:02 PM 8/9/2008, you wrote: >> I looked at those. The gypsum block sensors I'm finding are all like >> $20 a pop. Way more than I want to spend for a piece of each sensor. >> >> If you can point me to a supply that is significantly cheaper, please >> let me know! >> >> -Pete >> >> On Aug 9, 2008, at 7:50 AM, Grif w. keith griffith wrote: >> >>> >>> gypsum block sensor. Change every few years. >>> >>> >>> At 05:16 PM 8/8/2008, you wrote: >>>> Pretty coarse is fine. The intended application is to remain in >>>> place >>>> rather than being a portable probe. It is simply to provide some >>>> information back to a sprinkler controller. Target is consumers >>>> rather >>>> than commercial/large ag organizations. >>>> >>>> Basically I need something equivalent to a 10 point scale: bone dry >>>> to >>>> waterlogged. >>>> >>>> -Pete >>>> >>>> On Aug 8, 2008, at 3:51 PM, Grif wrote: >>>> >>>>> resistance/conductivity and moisture content do not track well. I >>>>> think with what I think I know, simple and cheap go together >>>>> nicely, >>>>> but reliably and accuracy may be a stretch. If the soil type >>>>> can be >>>>> characterised and stays stable,,, (like an orchard or vinyard over >>>>> time), conductivity/resistance may infact work fine. If it's a >>>>> portable unit, not sure you'll get to what you need. >>>>> >>>>> Units with good resolution seem to be tensioneters, that and his >>>>> hands are all my brother trusts (ag guy). Not fast if I remember. >>>>> The resistance ones seem to use a gypsum block encased resistance >>>>> element to make sure none of the "other" stuff affects the >>>>> resistance/ph around the sensor. >>>>> >>>>> Seems like the stablization time for any of the commercial ones >>>>> I'm >>>>> aware of is measured in hours, not seconds and minutes. >>>>> >>>>> What kind of accuracy do you need? >>>>> >>>>> -----Original Message----- >>>>>> From: Peter Loron >>>>>> Sent: Aug 8, 2008 3:19 PM >>>>>> To: "Microcontroller discussion list - Public." >>>>>> Subject: [EE] Replacement for L4620 >>>>>> >>>>>> Can anybody point me to a replacement for the ST Micro L4620? >>>>>> >>>>>> http://www.allelectronics.com/mas_assets//spec/L4620.pdf >>>>>> >>>>>> I'm looking for a simple, cheap way to reliably measure soil >>>>>> moisture, >>>>>> and am thinking about using an oscillating probe to measure >>>>>> resistance. This chip looks like it has everything I want all in >>>>>> one >>>>>> tidy bundle. >>>>>> >>>>>> Suggestions? >>>>>> >>>>>> Thanks! >>>>>> >>>>>> -Pete >>>>>> -- >>>>>> http://www.piclist.com PIC/SX FAQ & list archive >>>>>> View/change your membership options at >>>>>> http://mailman.mit.edu/mailman/listinfo/piclist >>>>> >>>>> -- >>>>> http://www.piclist.com PIC/SX FAQ & list archive >>>>> View/change your membership options at >>>>> http://mailman.mit.edu/mailman/listinfo/piclist >>>> >>>> -- >>>> http://www.piclist.com PIC/SX FAQ & list archive >>>> View/change your membership options at >>>> http://mailman.mit.edu/mailman/listinfo/piclist >>> >>> >>> W. Keith 'Grif' Griffith >>> N7IVS >>> >>> -- >>> http://www.piclist.com PIC/SX FAQ & list archive >>> View/change your membership options at >>> http://mailman.mit.edu/mailman/listinfo/piclist >> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist > > > W. Keith 'Grif' Griffith > N7IVS > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist