SparkFun Soil Moisture Sensor (with Screw Terminals)

The SparkFun Soil Moisture Sensor is a simple breakout for measuring the moisture in soil and similar materials. The soil moisture sensor is pretty straightforward to use. The two large, exposed pads function as probes for the sensor, together acting as a variable resistor. The more water that is in the soil means the better the conductivity between the pads will be, resulting in a lower resistance and a higher SIG out. This version of the Soil Moisture Sensor includes a 3-pin screw pin terminal pre-soldered to the board for easy wiring and setup.

To get the SparkFun Soil Moisture Sensor functioning, all you will need is to connect the VCC and GND pins to your Arduino-based device (or compatible development board). You will receive a SIG out, which will depend on the amount of water in the soil. One commonly known issue with soil moisture senors is their short lifespan when exposed to a moist environment. To combat this, we’ve had the PCB coated in gold finishing (ENIG, or Electroless Nickel Immersion Gold).

Note: Check the Hookup Guide below for assembly and weatherproofing instructions, as well as a simple example project that you can put together yourself!

Get Started with the Soil Moisture Sensor Guide

SparkFun Soil Moisture Sensor (with Screw Terminals) Product Help and Resources

Soil Moisture Sensor Hookup Guide

July 23, 2015

A quick hookup guide and project to get you started with the Soil Moisture Sensor from SparkFun.

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Core Skill: Programming

If a board needs code or communicates somehow, you're going to need to know how to program or interface with it. The programming skill is all about communication and code.

2 Programming

Skill Level: Rookie - You will need a better fundamental understand of what code is, and how it works. You will be using beginner-level software and development tools like Arduino. You will be dealing directly with code, but numerous examples and libraries are available. Sensors or shields will communicate with serial or TTL.
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Core Skill: Electrical Prototyping

If it requires power, you need to know how much, what all the pins do, and how to hook it up. You may need to reference datasheets, schematics, and know the ins and outs of electronics.

2 Electrical Prototyping

Skill Level: Rookie - You may be required to know a bit more about the component, such as orientation, or how to hook it up, in addition to power requirements. You will need to understand polarized components.
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Customer Comments

  • Wouldnt this device with its current over the terminals make the water sour?

    • By sour do you mean does the electricity alter the pH of the water? This probe acts as a voltage divider, so there is no current flowing across the probes, only through them. The probe itself should not be a problem. The gold and copper are fine for the plant, and the fiberglass is inert. Leaving the device on all the time can corrode the exposed PCB probes. However, it is suggested in the Hookup Guide that you not leave the probe on all the time and only power it when you want to take a measurement. This same method should result in the current flow not having any affect on the water composition. And even if it did, it shouldn’t be enough to affect the plant’s health as water would be replenished frequently enough to negate any side effects.

Customer Reviews

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I got some stange value

Hello, I am using this part since a couple of weeks. I am tetsing it with my plant and I am suprised to see some stange value (if it is). First I mesure the value with the sensor outside of the soil. It return me something like 12. The I insert in glass of fully dreid soil. It return me a value of 860. Then into a soil humid. It return me something like 700, and a soil dry. Instead of a value close to 100 or below 300, it return a value of 700.

Then I tried with my plant. I gave to my plant a lot of water and then inserted the sensor into soil for one week. At the begining, the sensor return me a value of 779. During the week, I expected to see the value going down, but not. Now the soil is fully dried and the sensor return me a value of 650. It’s strange because it should print a value below 300. If I remove the sensor from the soil, it print me a value of 12.

I do not understand when the soil is fully dried, I do not have a value below 300 or around 100.

FYI: I inserted the ¾ of the “legs” into the soil. If I insert only 50% of the legs, the values seam to be better…

Cheers

Sorry to hear about the trouble with the moisture sensor. Have you reached out to our technical support department? They can be reached at techsupport@sparkfun.com - they’re usually very good at helping make sense out of abnormal readings.