Integration of SDI-12 Sensors and circuit modification

Other Hardware General Electronics
1

Hi Everybody,

I am new in this forum. I am a french agronomist working on monitoring of physical parameters in agrosystems. I am developping a station based on the envirodiy SDI-12 library with Teros sensors from Decagon.

I am using the schema given in the Envirodiy documentation :

I read in the SDI-12 Documentation (page 4) and in the Teros 11/12 datasheet (page 3) that a minimal impedance was required when the transmiter is on or when the low power mode is activated.

When an SDI-12 device has its transmitter on, its direct current (DC) source resistance
must be greater than 1000 ohms and less than 2000 ohms

When any SDI-12
device’s transmitter is off, including during a low-power standby mode, the DC resistance to
ground must be within 160K to 360K ohms.

And especially (I am using a 3V alimentation and a 5V booster to supply sensors) :

If an SDI-12 sensor does not use the 12-volt line for
power, its data line resistance to ground while powered down must be within 160K to 360K ohms

My questions is :
– Are the components required in the circuit of the SDI-12 documentation/Teros data sheet (capacitors, resistance, …) already present in the sensor or is it compulsory and must be added to the circuit to supply and make the sensors working well?

For the moment, I have only one sensor using the envirodiy schema (it’s working well) and that’s why I want to know if the second schema from envirodiy is sufficient to use properly multiple sensors or if SDI-12 documentation modified circuit (resistance, capacitor, inductor) is needed to use them?

Thank you in advance for your advices.

2

Hi turfhacker, did you solve the problem to do works sdi12 data bus communication over 3.3V controllers?

Did you need some adapter circuit or lever conversor?

I tried itusing TXS0108E to convert signals 5v to 3.3 a s 3.3 to 5v, but I couldnt comunicate well.

After that, I tryusing another level converter with a transistor and I could comunicate only 1 sensor. The problem with this was when I conected several sensors to the sdi12 bus. Then,some sensors didnt comunicate well because data corrupted.

Please, could you tell me if you solve this problem and how?

Thank you very much.