Shade Net Automation: Light Sensor and Motor for Greenhouse

Shade net automation using a light sensor and motor for a greenhouse provides precise control of sunlight levels, protecting crops from high-intensity radiation while maximising photosynthesis during optimal light periods. Manual shade net operation is labour-intensive and inconsistent — automated systems driven by BH1750 light sensors and 12V DC motors ensure crops always receive ideal light conditions. This guide covers building a complete automated shade net retraction system with ESP32.

Table of Contents

• Why Shade Net Automation Matters
• Crop Light Requirements and Shade Net Specifications
• Components Required
• Circuit and Motor Control Design
• ESP32 Shade Net Controller Code
• Safety Features and Wind Override
• Indian Greenhouse Applications
• Frequently Asked Questions

Why Shade Net Automation Matters

Shade nets are used extensively across Indian horticulture to manage light intensity and reduce heat stress. Manual operation challenges include:

• Labour cost: Shade net deployment/retraction takes 30-90 minutes for a large greenhouse — 2-3 times daily
• Timing errors: Nets deployed too late on clear mornings cause early heat stress; retracted too early in evening wastes potential photosynthesis time
• Night deployment: Nets left closed on clear nights reduce dew absorption on foliage and can damage sensitive crops in cold weather
• Storm response: Manual retraction during sudden wind gusts is dangerous and often impossible in time — damage to nets and structures occurs

Automated shade net systems save 1-2 labour hours daily and improve crop light interception uniformity by 20-35% compared to manual operation.

Crop Light Requirements and Shade Net Specifications

Note: 1 lux = 0.0079 W/m2 (for daylight). Full summer sunlight in India = 100,000-120,000 lux. Common shade nets: 25%, 35%, 50%, 65%, 75% shading factors (HDPE knitted nets).

Components Required

Full system components:

• ESP32 WROOM-32
• BH1750 digital light intensity sensor (0-65535 lux, I2C)
• BME280 temperature and humidity sensor
• Rain sensor module (for emergency retract)
• Wind speed sensor (anemometer, for storm protection)
• 12V DC gearbox motor (5-15 RPM, torque-rated for net weight and span)
• L298N H-bridge motor driver (or 2x relay for simple direction control)
• Limit switches (2x end-of-travel, to prevent motor overrun)
• 12V 10A power supply (motor is primary load)
• Rope and pulley system or roller tube for net deployment

Circuit and Motor Control Design

Using L298N H-bridge for motor direction control:

• L298N IN1 -> ESP32 GPIO26, IN2 -> GPIO27 (direction control)
• L298N ENA -> GPIO25 (PWM speed control, optional)
• L298N OUT1/OUT2 -> DC motor terminals
• Limit switch 1 (net fully open) -> GPIO14 (pulled HIGH, LOW = triggered)
• Limit switch 2 (net fully closed) -> GPIO12 (pulled HIGH, LOW = triggered)
• BH1750 SDA -> GPIO21, SCL -> GPIO22
• BME280 SDA -> GPIO21, SCL -> GPIO22 (I2C shared)
• Rain sensor DOUT -> GPIO13

Motor sizing: For a 10m span shade net, a 12V 10Nm gearbox motor at 5-10 RPM is sufficient. Calculate required torque = (net weight kg x span/2 m) + 30% safety margin for friction. Stainless steel guide wires prevent net sag.

ESP32 Shade Net Controller Code

#include <Wire.h>
#include <BH1750.h>
#include <Adafruit_BME280.h>
#include <WiFi.h>
#include <WebServer.h>

BH1750 lightSensor;
Adafruit_BME280 bme;
WebServer server(80);

// Motor control
#define MOTOR_IN1    26
#define MOTOR_IN2    27
#define LIMIT_OPEN   14  // Low = net is fully open
#define LIMIT_CLOSE  12  // Low = net is fully closed
#define RAIN_SENSOR  13

// Light thresholds
const float LUX_OPEN_THRESHOLD  = 80000; // Deploy net above this (lux)
const float LUX_CLOSE_THRESHOLD = 50000; // Retract net below this (lux)
const float TEMP_OPEN_THRESHOLD = 35.0;  // Deploy net above this temperature

// States
enum NetState { NET_OPEN, NET_CLOSED, NET_MOVING, NET_MANUAL };
NetState netState = NET_CLOSED;

bool netOpen     = false; // Approximate state (between limits)
bool rainActive  = false;
float currentLux = 0;
float currentTemp = 0;

void motorOpen() {
  if (digitalRead(LIMIT_OPEN) == LOW) { motorStop(); return; } // Already at limit
  digitalWrite(MOTOR_IN1, HIGH);
  digitalWrite(MOTOR_IN2, LOW);
  netState = NET_MOVING;
  Serial.println("Motor: Opening net");
}

void motorClose() {
  if (digitalRead(LIMIT_CLOSE) == LOW) { motorStop(); return; }
  digitalWrite(MOTOR_IN1, LOW);
  digitalWrite(MOTOR_IN2, HIGH);
  netState = NET_MOVING;
  Serial.println("Motor: Closing net");
}

void motorStop() {
  digitalWrite(MOTOR_IN1, LOW);
  digitalWrite(MOTOR_IN2, LOW);
  if (digitalRead(LIMIT_OPEN) == LOW) {
    netState = NET_OPEN;
    Serial.println("Net: OPEN (limit reached)");
  } else if (digitalRead(LIMIT_CLOSE) == LOW) {
    netState = NET_CLOSED;
    Serial.println("Net: CLOSED (limit reached)");
  } else {
    netState = NET_MANUAL;
  }
}

String buildDashboard() {
  String html = "<!DOCTYPE html><html><head><title>Shade Net Control</title>";
  html += "<meta name='viewport' content='width=device-width,initial-scale=1'>";
  html += "<meta http-equiv='refresh' content='15'></head><body style='font-family:sans-serif;text-align:center'>";
  html += "<h1>Shade Net Controller</h1>";
  html += "<p>Light: <b>" + String(currentLux, 0) + " lux</b></p>";
  html += "<p>Temperature: <b>" + String(currentTemp, 1) + " C</b></p>";
  html += "<p>Rain: " + String(rainActive ? "Yes - net deployed" : "No") + "</p>";
  String stateStr = (netState == NET_OPEN) ? "OPEN" : (netState == NET_CLOSED) ? "CLOSED" : "MOVING";
  html += "<p>Net Status: <b>" + stateStr + "</b></p>";
  html += "<a href='/open'><button style='padding:12px 24px;margin:8px'>Open Net</button></a>";
  html += "<a href='/close'><button style='padding:12px 24px;margin:8px'>Close Net</button></a>";
  html += "<a href='/stop'><button style='padding:12px 24px;margin:8px;background:red;color:white'>STOP</button></a>";
  html += "</body></html>";
  return html;
}

void setup() {
  Serial.begin(115200);
  Wire.begin(21, 22);
  lightSensor.begin();
  bme.begin(0x76);

  pinMode(MOTOR_IN1, OUTPUT); digitalWrite(MOTOR_IN1, LOW);
  pinMode(MOTOR_IN2, OUTPUT); digitalWrite(MOTOR_IN2, LOW);
  pinMode(LIMIT_OPEN,  INPUT_PULLUP);
  pinMode(LIMIT_CLOSE, INPUT_PULLUP);
  pinMode(RAIN_SENSOR, INPUT_PULLUP);

  WiFi.begin("FarmWiFi", "farmpassword");
  while (WiFi.status() != WL_CONNECTED) { delay(500); }
  Serial.println("IP: " + WiFi.localIP().toString());

  server.on("/", []() { server.send(200, "text/html", buildDashboard()); });
  server.on("/open",  []() { motorOpen();  server.sendHeader("Location", "/"); server.send(302); });
  server.on("/close", []() { motorClose(); server.sendHeader("Location", "/"); server.send(302); });
  server.on("/stop",  []() { motorStop();  server.sendHeader("Location", "/"); server.send(302); });
  server.begin();
}

void loop() {
  server.handleClient();

  static unsigned long lastCheck = 0;
  if (millis() - lastCheck > 30000) { // Check every 30 seconds
    lastCheck = millis();

    currentLux  = lightSensor.readLightLevel();
    currentTemp = bme.readTemperature();
    rainActive  = (digitalRead(RAIN_SENSOR) == LOW);

    // Stop motor immediately if limit reached
    if (digitalRead(LIMIT_OPEN) == LOW  && netState == NET_MOVING) motorStop();
    if (digitalRead(LIMIT_CLOSE) == LOW && netState == NET_MOVING) motorStop();

    // Auto control logic (only when not in manual override)
    if (netState != NET_MANUAL) {
      if (rainActive && netState != NET_OPEN) {
        motorOpen(); // Open net in rain (prevents waterlogging on net surface)
      } else if ((currentLux > LUX_OPEN_THRESHOLD || currentTemp > TEMP_OPEN_THRESHOLD)
                 && netState == NET_CLOSED) {
        motorOpen(); // High light or temperature: deploy shade net
      } else if (currentLux < LUX_CLOSE_THRESHOLD && !rainActive
                 && netState == NET_OPEN && currentTemp < TEMP_OPEN_THRESHOLD) {
        motorClose(); // Light dropped: retract shade net
      }
    }
    Serial.printf("Lux:%.0f T:%.1fC Rain:%s Net:%sn",
      currentLux, currentTemp, rainActive?"Yes":"No",
      netState==NET_OPEN?"OPEN":"CLOSED");
  }
  delay(100);
}

Safety Features and Wind Override

Critical safety features for outdoor shade net systems:

• Limit switches: Mechanical stop prevents motor overrun at both ends of travel — most important safety feature
• Motor timeout: If motor runs for more than 3 minutes without reaching a limit switch, stop immediately (net jam or obstruction)
• Wind speed cutoff: Above 40 km/h wind, retract shade net immediately (unloaded net acts as a sail, damaging structure)
• Rain retract logic: Open (retract) shade net during heavy rain — closed nets accumulate water weight causing structural damage
• Manual override button: Emergency stop accessible from inside greenhouse
• Power failure protection: On power restoration, read limit switches to determine actual net position before any movement

Indian Greenhouse Applications

Shade net automation is particularly impactful across India:

• Floriculture (Bengaluru, Pune, Delhi NCR): Rose, gerbera, and chrysanthemum exports require tight light control. Automated systems allow night staff reduction.
• Capsicum (Maharashtra, Karnataka): 35% shade net deployment at PAR above 1200 umol/m2/s prevents sun scald on fruits.
• Ornamental nurseries (Kolkata, Chennai): Shade-loving indoor plants (peace lily, dracaena) require 65-75% shade year-round.
• Strawberry (Mahabaleshwar, Himachal): Clear UV-blocking nets allow full light but reduce UV stress on berries, improving colour and shelf life.

Frequently Asked Questions

What motor torque do I need for a 10-metre shade net span?

For a 10m x 30m HDPE shade net (weight approximately 2 kg/m2 x 300 m2 = 600 kg for a full structure), the deployment mechanism works on half the span (5m moment arm) with friction reduction from guide wires. A 12V 20-30 Nm gearbox motor at 5 RPM is sufficient for most polyhouse shade net systems. Always oversize by 50% for reliability.

Can I use this system for motorised privacy screens or awnings?

Yes, the same circuit and logic applies to any motorised fabric system. Adjust the light thresholds to suit your application — for privacy screens, add a manual-only mode that ignores light sensor readings.

How do I calibrate the BH1750 sensor for shade level measurement?

The BH1750 measures lux accurately (within 5%) without calibration. For shade level mapping, take readings simultaneously inside and outside the shade net during clear sky conditions. Shade percentage = (1 – indoor lux/outdoor lux) x 100. Verify against the manufacturer-stated shade factor of your specific net.

What shade net percentage is best for Indian summer conditions?

For most vegetable crops in India (March-June), 35-50% shade nets are optimal. Above 50%, CO2 assimilation drops significantly due to light limitation. Below 35%, heat stress occurs despite ventilation in plains regions above 35 degrees C ambient. For coastal and hill regions, 25% shade is often sufficient due to naturally lower radiation levels.

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