The Observant C3 and Observant Solo have a single SDI-12 port however it is still possible to connect more than one SDI-12 device at a time.
Option 1: Power Devices Separately
This is usually the best and simplest option, so long as you have enough spare output ports on your C3. It's not possible on the Solo however.
The idea is that you will power each device from a seperate power pin, ensuring that only one is powered up at a time, thus preventing them talking over the top of one another on the SDI-12 port.
Below is an example wiring:
| C3 |
Sensor 1 | Sensor 2 | Sensor 3 | |
| Port | Label | Wire | Wire | Wire |
| RS232/SDI | + | Sensor Power (usually brown or red) | - | - |
| RS232/SDI | Rx | SDI-12 / Data | SDI-12 / Data | SDI-12 / Data |
| RSR232/SDI |  |
Ground | Ground | Ground |
| Output | 1 | - | Sensor Power (usually brown or red) | - |
| Output | 2 | - | - | Sensor Power (usually brown or red) |
You can use the same concept to install up to a total of 5 SDI-12 devices (subject to battery considerations), by using all 4 output ports.
Option 2: Set Unique Addresses
Use this option is you already have devices using the output ports or if you're using a Solo.
SDI-12 is a serial communications protocol supported by a wide range of sensors. SDI-12 is an 'addressed' protocol, meaning that each sensor has its own address number, and if more than one sensor is connected to the same SDI-12 port.
There are 2 important steps to consider:
- Wiring multiple sensors to a single SDI-12 port
- Ensuring both sensors have different SDI-12 addresses
Wiring Multiple Sensors to a Single SDI-12 Port
- C3 - wire both sensors directly to the SDI-12/RS-232 port
- Solo - use the Solo sensor accessory pack (#10125) and cable junction accessory pack (#10124)
Changing the SDI-12 Address
The SDI-12 communication protocol allows for multiple devices on the same bus (wires), so long as no two devices have the same address.
To do so, you'll need to set the address on the probes themselves, which is usually done by downloading the probe manufacturer's configuration program, plugging the probe into your computer and configuring the address. If you can't find instructions how to do this on the manufacturer's website, feel free to connect our Support team for help.
You'll then wire the probes on the C3 or Solo's SDI-12 port in parallel, which just means that every probes Power, Tx, Rx and ground wires are all connected together.
Finally, you need to tell the C3 or Solo which address you've programmed each probe for, this is done by setting the address in Manage Equipment, under the soil probe's 'Settings' menu.