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[Reply #15 on:]

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)..

[Reply #16 on:]

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.