Moisture-Duck Sensor: Measure Soil Moisture with ATtiny13A and Duck-like Precision

In this video, I'll explore several different methods for measuring soil moisture, including gravimetric, neutron probe, tensiometer, time domain transmissometry, time domain reflectometry, capacitive, and resistive methods. I'll explain how each method works and discuss their advantages and limitations.

I'll also show you how to make your own DIY soil moisture sensor PCBs for the capacitive and resistive methods. For the capacitive sensor, I'll be using an MSP430 microcontroller and for the resistive sensor, I'll be using an ATtiny13A microcontroller. I'll go over the design and assembly process step-by-step, and provide all the necessary code and schematic files.

Whether you're a gardener looking to optimize your watering schedule, a farmer managing large-scale irrigation systems, or a student or researcher studying soil moisture dynamics, this video will provide valuable insights and practical knowledge for measuring soil moisture using different methods and building your own custom sensors.

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Link to the project files:

▬ Contents of this video ▬▬▬▬▬▬▬▬▬▬
0:00 - Intro & summary
0:20 - Gravimetric Method
1:13 - Neutron Probe Method
2:03 - Tensiometer Method
3:43 - Time Domain Reflectometry (TDR)
4:57- Time Domain Transmissometry (TDT)
5:22 - Capacitance Sensors
9:09 - Resistive Sensors
9:46- Test of Corrosion on Resistive Sensors
12:14 - Making the Schematics & PCB
14:15 - Summary

[Aleksei_R]

I used resistive fork from aliexpress like in your video long time ago. Beat the corrosion was very easy. I cut off the pcb fork with corroded copper and soldered stainless steel electrodes to the remaining part. I took stainless steel from used car wiper.(rubber part is held by two ss plates)Cut the Stainless to the same lenghts as pcb was and insert to the pot, so the moisture and soil only contacts stainless plates and not solder or pcb.

[AdityaMehendale]

I am planning to make s similar device, with some differences:
1) small solar cell instead of battery; flashing LED instead of buzzer
2) Preferably no MCU - just CMOS/digital; ATTiny, MSP430 STM32 as a last resort.
3) It is true that DC corrodes the electrodes. Also correct that capacitance method in side-by-side electrodes if iffy. This can be countered by having face-to-face electrodes with a water-permeable membrane (e.g. a sheet of microfiber "paper") sandwiched between coated electrodes. Permittivity-changes should IMO become obvious and clear in this configuration. The paper may eventually get contaminated by stuff in your potting soil. Resistance-measurement is also possible, but IMO "AC" measurement (i.e. with an AC biasing stimulus, with each electrode having a series-capacitor) would eliminate galvanic corrosion even if you did not run the device intermittently. The problem with DC interfaces is that even very small leakage currents, over extended periods, shall eat away the electrodes (and cause electropotentials) whereas the DC-insulation offered by a plastic-film capacitor is outstanding, robust and cheap.
4) about your "GHz" problem: (out of academic interest) --> An ESP32 has a 2.4 GHz pin, and RSSI indicator ;) - I wonder if this can be repurposed for humidity measurement. (self-attenuation due to moist soil)

[neworginallogin]

I wonder if you could use graphite probes (like pencil cores) to reduce corosion even more

[hanyanglee]

what about rf energy, like 50mhz, does water block it ?
Or if water changes Z0 of a coax, it should be possible to test it.

[zoenagy]

There wasnt any conclusion, are you saying resistive is better than captive?