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Author Topic: Sensor Interfacing: Soil Moisture Sensor using SDI-12  (Read 5883 times)
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Hi quatch you are right I tried the softwareSerial method but can not get anything from SDI-12. But I do get data reading using the DDI serial communication protocol, which is based on 8N1 and non-inverted, and I can use other pins (right now Pin 7 as RX to receive data).If you are interested you may try this as well, the disadvantage is that you need a single pin for each sensor (maybe mux can help)..
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This is true for decagon devices, I'd forgotten about it as I was also working with a stevens hydra probe (SDI version) which doesn't have a friendly DDI startup. Actually the decagon manuals have a very nice description of SDI12, easier to read I think than the official specification (I do see that the manual for the 5TE and GS3 disagree as to whether DDI is active high[yes] or active low[no]).. Of course they insist on a nonstandard 3.3V, but that can be advantageous nowadays.

As long as you only need the measurements that are pre-programmed for the DDI burst, you're golden. A multiplexer would work great, but you'll also need to be able to supply and remove power to toggle the measurements.
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Hi all,

I'm considering of buying GS3 sensor from Decagon as well in order to connect it to Arduino MEGA using serial DDI (not SDI-12). And I am quite concerned about the "active-high logic levels using 0-3.6V", and then I founf this post.

My question is that if I connect the sensor directly to Serial1 in arduino mega I guess that it wont work straightaway, is that correct? And in that case, could you tell me the circuit that I would need??

I would appreciate any help.

Cheers
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Yeah, DDI is just normal serial. A real shame the interface isn't completely DDI..

The voltage is high enough that it should be read by a 5V arduino. You won't be able to transmit back (but with DDI there is no reason to).
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Hi Guys

Long time lurker first time poster.  anyway I just made a Library that does exactly this and I would love some feedback

https://github.com/joranbeasley/SDISerial

-Joran
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