What it shows
Two soil moisture probes in two pots each control their own 5 V pump through a relay, and a NodeMCU shows both moisture levels and pump states on a phone page. It demonstrates zone-wise watering, the way a farm drip system treats each bed separately.
The science
A capacitive probe measures how much the soil changes the capacitance of a track; wet soil has a higher dielectric constant, so the output voltage falls. The NodeMCU has a single analog pin, so the two probes are powered from two digital pins and read one at a time: power probe 1, read A0, power it down, power probe 2, read. Each zone has its own dry and wet thresholds with hysteresis. The web server builds a page that refreshes every three seconds and lets the user water a zone by hand.
Materials
Cost: under Rs 1,500. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A NodeMCU ESP8266 and USB cable
- Two capacitive soil moisture sensors (v1.2)
- A 2-channel 5 V relay module
- Two 5 V submersible mini pumps with tube
- A CD4051 or a second analog trick: one 10 kΩ resistor per probe (see steps)
- Two small pots with soil and a water tub
- A 5 V 2 A supply or power bank
Safety
For this project: Pumps and water stay in a tray away from the board. Only 5 V pumps are switched. An adult must check the supply wiring.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
9 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Wire both probes with GND to GND and AOUT joined to A0; power probe 1 VCC from D1 and probe 2 VCC from D2 so only one is on at a time.
Wire the relay INs to D5 and D6 and the pumps through COM and NO to the separate 5 V supply, grounds joined.
Put each probe in its pot up to the line, and each pump tube into its pot.
Read each probe dry and after watering; note the two values per zone.
Write a read function: set D1 high, wait 50 ms, read A0 ten times and average, set D1 low; repeat for D2.
For each zone, start its pump when the reading is above the dry value and stop when it falls below the wet value.
Limit any pump run to 10 seconds then wait 60 seconds so a loose probe cannot flood a pot.
Serve a page with two bars and two Water now buttons, refreshing with a meta refresh tag.
Let one pot dry overnight and show that only its pump runs in the morning.
What you should see
Each pot is watered only when its own probe reads dry; the phone page shows both levels and which pump is running.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why capacitive probes instead of the two-prong resistive type?
Resistive prongs corrode in weeks because current flows through the soil; capacitive probes are coated and last.
2Why power the probes from digital pins?
So two probes can share the one analog pin by switching each on only when it is read.
3Why cap the pump run time?
If a probe falls out of the soil it reads dry forever; the cap prevents emptying the tub into one pot.
4What is a drip system?
Pipes with small emitters that deliver water slowly at the root, wasting far less than flooding.
Take it further
Log readings every ten minutes to a free cloud sheet and plot how fast each soil dries.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.