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I bought a 'Soil Moisture Sensor' like this https://www.tiagoespinha.net/wp-content/uploads/2014/05/2014-05-09-12.51.20.jpg from ebay, and it turns out it's really nothing of the sort (just a resistance meter, with an analog output and a manually configurable comparitor circuit to give a higher/lower type digital output).

Does anyone know of anything on ebay that packages up a better solution. I have 4 large beds and a 4 shelf plastic greenhouse, and would like to monitor and hence control the watering with a series of networked Pi's, so want a relatively cheap solution that I can connect multiple instances of to one of 5 Pi's, that can give me a reading on which bits of the beds are drying out etc.

I suspect the device I have, is a good start, but would need some kind of ADC converter, ideally that I could connect to a USB bus, or to one of a number of GPIOs, but I don't really want to buy lots of PiFace boards, when all I need is a cheap ADC/resistance solution.

Answer So following research from @Mark Wagoner's suggestion to use a SHT-10 based sensor, I found a couple of things.

  1. Firstly that I probably want a gypsom block tensiometer, to sense soil moisture (basically 2 probes in a porus ceramic, such as 2xA2 or Galvanised nails in a block of Plaster of Paris), and
  2. Secondly I need a cheap ADC circuit to read those resistances into the pi.

So in solution, I found the following:-

Extra I found this http://www.trickle-l.com/new/sensors/ which is a handy list of options for sensing soil moisture

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  • Having done a bit of research, it seems the best approach from a sensing point of view is a tensiometer, which is to say measuring the resistance accross a porus ceramic. This chap has got instructions to make something out of galvanised nails, plaster of paris and a bit of hose, and it sounds plausible cheapvegetablegardener.com/… But I still need a means to get the resistance to the pi via some kind of ADC.
    – sibaz
    Jan 13, 2016 at 13:04

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Not from eBay but have you looked at this?

Soil Temperature/Moisture Sensor - SHT10

They also have a tutorital on how to hook everything up.

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  • It looks good, but as I'll probably want 12 or 16 of them, I was hoping for something around the 10GBP/15USD rather than 45/50USD. A good thought though.
    – sibaz
    Jan 13, 2016 at 12:42
  • Looks like the SHT-10 has some potential, with it's serial data line, and it's <5GBP per chip, if I just connect it directly. Need to figure out if thats feasible though. ebay.co.uk/itm/…
    – sibaz
    Jan 13, 2016 at 12:46
  • Definite potential with the SHT10. Many thanks raspberrypi.org/forums/viewtopic.php?f=37&t=78939
    – sibaz
    Jan 13, 2016 at 12:49
  • Hmm, seems the SHT10 is only an air Humidity testor, and isn't reliable for soil measuring. I'm intending to encase whatever circuitry I make in silicon and bury it, with wires connecting to my Pi in a water tight box, so this needs to work under soil.
    – sibaz
    Jan 13, 2016 at 12:54

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