> For the complete documentation index, see [llms.txt](https://faq.growsensor.co/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://faq.growsensor.co/substrate-probes/how-do-i-connect-a-substrate-probe-to-the-grow-sensor-using-the-sdi-12-connector-block.md).

# How do I connect a substrate probe to the Grow Sensor using the SDI-12 connector block?

To connect a compatible SDI-12 substrate probe to your Grow Sensor, follow these steps:

### What you’ll need

You’ll need to purchase the SDI-12 connector kit from our website. This includes:

* 1 x SDI-12 connector block
* 1 x RJ12 cable (included)

### Step-by-step setup

{% stepper %}
{% step %}
**Connect the cable:**

* Plug the RJ12 cable into the bottom port of your Grow Sensor.
* Plug the other end of the RJ12 cable into your SDI-12 connector block.
  {% endstep %}

{% step %}
**Choose your wiring method based on your probe:**

* **Option A: Bare wire probe**
  * If your substrate probe has three bare wires at the end:
  * Use a small flathead screwdriver to open the SDI-12 connector. There are notches on either side of the case—insert the screwdriver into a notch and gently twist to pop the case open.
  * Inside the connector, you’ll find three labeled screw terminals:
    * Power (typically red or brown)
    * Ground (typically black)
    * Data (typically white or yellow)
  * **Important**: Most soil substrate probes list the wire colours and their corresponding functions on their product page or datasheet. Please refer to this information and double-check before wiring to ensure you connect each wire to the correct terminal.
  * Insert the wires, tighten the terminal screws, and close the case.
* **Option B: Probe with a headphone jack**
  * If your substrate probe has a 3.5mm headphone-style jack, you can:
    * **Option 1:** Cut off the jack, strip the wires, and follow the steps in Option A.
    * **Option 2:** Use a female headphone socket, wire that into the SDI-12 connector, and plug in the probe.
      {% endstep %}
      {% endstepper %}

### A quick note on durability

We’ve designed the SDI-12 connector to be as affordable and accessible as possible. While the case can be opened and closed, it’s not built for repeated use.

\
Once you’ve wired in your substrate probe correctly, we recommend keeping the connector closed permanently to avoid wear or potential damage.

### Final checks

* Make sure your substrate probe is SDI-12 compatible and supported by the Grow Sensor.
* Once connected, your probe should begin reporting substrate readings in the Grow Sensor app.
* Open your grow in the app, go to Calibration settings, and select the correct substrate medium (e.g. soil, coco, rockwool) to ensure accurate readings.

Let us know if you’d like a wiring diagram or setup video — we’re happy to help!


---

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