Damaged Soil Moisture Sensor Upgrade

I hope this simple instrucable will help some folks out there like me who like to use these cheap soil sensors in their projects. I found that over time the sensor will corrode and become of no use, so I decided to upgrade them so to speak with some simple 24 gauge stainless steel wire to make them last even longer after they have become useless. This simple upgrade has given a lot longer lifespan to these cheap sensors.

Notice in the image that one side has corroded to the point that the sensor is no longer usable.

Step 1: Tools and Material Needed.

• Tweezers, Small Flat Head or Scratching Awl
• Stainless Steel Wire (I use 24 gauge) found on Amazon pretty cheap.
• Wire Cutters
• Soldering Iron and Solder
• Old Soil Moisture Sensor
• Clamp and Fan - Hold the parts while soldering and also help draw away the solder fumes.

Step 2: Scratch & Awl

I take and scratch away the coating just above the sensors exposed metal strips that corrode with time. While I didn't calculate or do all the math involved to be certain the readings would be super accurate after the upgrade. The sensors still work like before and I've had them last for many months now.

Step 3: Cut and Tin

Cut and tin the wires on one end and then straighten them as best as possible. Does not have to be perfect. Do your best. :)

Step 4: Tin the Pads

Now lets tin the pads we scratched off earlier and solder the new stainless steel wires we just tinned to the sensor.

Step 5: Cut and Done.

Now that we have the new wires added to the sensor we can cut off the additional wire hanging over the ends and you're done.

I have successfully been using these types of upgrades on sensors for months now. The original sensor depending on how ofter you probe for data will usually only last a month at best if you do not change the polarity in your code every once in awhile. Regardless, this is a quick, cheap and easy fix for those sensors that have already been damaged. Happy time folks!

Comments

[JJ Slabbert]

I will suggest capacitive soil moisture sensors. DFrobot and a few companies produce them. Higrow attached one two an ESP32. Capacitive sensors have no metal in contact with soil.

[MikB]

They "corrode" because of electrolysis. The metal from one electrode is driven off into the soil of the plant, which is not great news for the plants :)

This is because most of these soil/water level sensors use DC to sense. The only way to really stop this is to use an AC sensing current, or very intermittent probing with a low DC current (which will delay the inevitable). Either way, it is slightly harder work.

[Challon]

Thanks for the comment MikB. There are other things that can be done to help save the sensor, like every other time the sensor runs, change the polarity of the current. I've seen some arduino code that will do this before but I've never taken the time to add it to my code. (Which I will in the future) The reason for corrosion happening so fast in my case is, proof of concept designs in soil (no plant) probing way more often than needed. I'll be posting my plant sensor design and instructable soon. Thanks again for your wisdom and wise words.

[MikB]

If you change the polarity of the current every time you probe, that would constitute AC, although VERY low frequency :) It will do wonders for the life of the probe.

The worst case is a constant DC current, just left there to eat the sensors :(

[Challon]

Yep, I understand AC and DC current very well. I've just not added the code because I can never seem to find time to play with those sensors, that is changing very soon and I'll post up what I have built. I have some that are just sensors with LED?Neopixel displays that change colors to let you know what the moisture levels are as well as some RF models that communicate with my Vera to notify via text/email along with the LED/Neopixel visual aspect.