Mohammad Taha
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Hardware prototypeBuilt solo

Smart Irrigation System

IoT irrigation controller — ESP8266 + Blynk

An ESP8266 NodeMCU reads a soil-moisture sensor every second, waters through a relay-driven pump when the soil is dry, and reports to a Blynk dashboard where the pump can also be switched by hand. The watering logic is a small non-blocking state machine.

Source on GitHub
Wiring diagram: soil moisture sensor and relay connected to an ESP8266 NodeMCU, a 9V battery driving a mini pump, and a power bank, linked to Blynk over Wi-Fi.
Built with
C++ (Arduino)ESP8266 NodeMCUBlynk IoT
Type
Personal project
Source
Public on GitHub

How it decides

Soil reading → pump decision

Sensor & remote inputFirmware decidesevery 1 sV2on until offSoil sensoranalog A0Blynk appmanual switchBlynk cloudV0 V1 · V2Threshold> 800 means dryOverrideBLYNK_WRITE(V2)State machinepump 3 s · wait 40 sRelayactive-LOW · D1Pumpmini DC pumpSensor & remote inputFirmware decidesevery 1 sV2on until offSoil sensorBlynk appBlynk cloudThresholdOverrideState machineRelayPump
  • person
  • guesses / untrusted
  • decides
  • process
  • storage
  • third party
  • trust boundary

Boundary Where guessing stops and something deterministic decides.

  • Dry (> 800) → pump on for 3 s → ignore readings for 40 s → act again. code
  • Non-blocking: millis() comparisons, no delay(). code
  • Relay pin is driven HIGH at boot so the pump starts off. code
The drawing, in words

Smart Irrigation System: Soil reading → pump decision. Left of the redline is “Sensor & remote input”; right of it is “Firmware decides”.

  • Soil sensor — analog A0 (Sensor & remote input)
  • Blynk app — manual switch (Sensor & remote input)
  • Blynk cloud — V0 V1 · V2 (Sensor & remote input)
  • Threshold — > 800 means dry (Firmware decides)
  • Override — BLYNK_WRITE(V2) (Firmware decides)
  • State machine — pump 3 s · wait 40 s (Firmware decides)
  • Relay — active-LOW · D1 (Firmware decides)
  • Pump — mini DC pump (Firmware decides)

Connections

  • Soil sensor → Threshold (every 1 s)
  • Blynk app → Blynk cloud
  • Blynk cloud → Override (V2)
  • Threshold → State machine
  • State machine → Relay
  • Override → Relay (on until off)
  • Relay → Pump
Blynk mobile dashboard for the Smart Irrigation System showing a moisture gauge at 729 and a pump switch.
Blynk web console for the Smart Irrigation System with a moisture gauge and pump control.

What was built

  • Circuit with an ESP8266 NodeMCU (ESP-12E), soil-moisture sensor, single-channel relay and mini DC pump. repo docs
  • Firmware that pushes moisture to Blynk virtual pins V0/V1 and listens for a manual switch on V2. code

My part

  • Built solo: circuit, firmware and Blynk dashboard. stated

Limits and open work

  • The README wiring table lists D2 for the relay while the firmware drives D1 — the docs drifted from the code. code
  • Runs on batteries and a power bank; solar power and a tank-level sensor are listed as next steps. repo docs

Decisions worth knowing

  • Water, then wait

    A reading above 800 means dry. The pump runs for 3 s; then for 40 s the firmware keeps reading and reporting but won't act, giving the water time to soak in. One dry reading can't flood the pot.

    code

  • Never block the radio

    Timing uses millis() comparisons instead of delay(), so Wi-Fi and Blynk keep running while the pump is on.

    code

  • Start safe

    The relay is active-LOW, so the pin is driven HIGH at boot and the pump starts off.

    code

A closer look

moisturepumpstate> 800 = dry3 swait 40 s — no reading acted onread again0s10s20s30s40s
Figure — one watering cyclecode Threshold and timings are the firmware's constants; the moisture curve is illustrative.