1. Greenhouse Automation

Combine a DHT22 and capacitive soil sensor. Temperature hysteresis controls the fan; short watering pulses and a cooldown protect the pump. PxServ enables the system and exposes every decision.

Level: Advanced · Time: 70 minutes

Design goals

Schedule multiple sensor and actuator tasks without long blocking delays
Prevent relay chatter around a threshold with hysteresis
Limit pump run time and repeat frequency
Stop outputs on invalid sensor data or configuration

Safety and wiring

Use only low-voltage DC loads, suitable relay/MOSFET drivers, external power, common GND, and inductive-load protection. Keep water physically separated from electronics. The sketch assumes active-low drivers.

Part	ESP32
DHT22 DATA	GPIO 4
Soil sensor AOUT	GPIO 34
Fan driver IN	GPIO 25
Pump driver IN	GPIO 26

Create greenhouse/system-enabled=1, greenhouse/fan-on=30, greenhouse/fan-off=28, and greenhouse/watering-threshold=30.

Complete sketch


#include <PxServ.h>
#include <DHT.h>
 
const char* WIFI_SSID = "your_wifi_ssid";
const char* WIFI_PASSWORD = "your_wifi_password";
const char* PXSERV_API_KEY = "your_pxserv_api_key";
const int DHT_PIN = 4, SOIL_PIN = 34, FAN_PIN = 25, PUMP_PIN = 26;
const int DRY_VALUE = 3000, WET_VALUE = 1400;  // Calibrate
const unsigned long PUMP_RUN_MS = 5000;
const unsigned long PUMP_COOLDOWN_MS = 60000;
 
PxServ client(PXSERV_API_KEY);
DHT dht(DHT_PIN, DHT22);
bool systemEnabled = true, fanOn = false, pumpOn = false;
float fanOnAt = 30.0, fanOffAt = 28.0;
int wateringThreshold = 30;
unsigned long pumpStartedAt = 0, pumpStoppedAt = 0;
unsigned long lastSensorAt = 0, lastConfigAt = 0;
 
void setOutput(int pin, bool enabled) {
  digitalWrite(pin, enabled ? LOW : HIGH);
}
 
void setPump(bool enabled) {
  pumpOn = enabled;
  setOutput(PUMP_PIN, enabled);
  if (enabled) pumpStartedAt = millis();
  else pumpStoppedAt = millis();
}
 
void readConfig() {
  PxServ::Callback active = client.getData("greenhouse/system-enabled");
  if (active.status == 200) systemEnabled = active.data == "1";
  PxServ::Callback onValue = client.getData("greenhouse/fan-on");
  if (onValue.status == 200) fanOnAt = onValue.data.toFloat();
  PxServ::Callback offValue = client.getData("greenhouse/fan-off");
  if (offValue.status == 200) fanOffAt = offValue.data.toFloat();
  PxServ::Callback soilValue = client.getData("greenhouse/watering-threshold");
  if (soilValue.status == 200) {
    wateringThreshold = constrain(soilValue.data.toInt(), 0, 100);
  }
}
 
void safeStop(String reason) {
  fanOn = false;
  setOutput(FAN_PIN, false);
  if (pumpOn) setPump(false);
  client.setData("greenhouse/status", reason);
}
 
void setup() {
  Serial.begin(115200);
  pinMode(FAN_PIN, OUTPUT); pinMode(PUMP_PIN, OUTPUT);
  setOutput(FAN_PIN, false); setOutput(PUMP_PIN, false);
  analogReadResolution(12);
  dht.begin();
  PxServ::connectWifi(WIFI_SSID, WIFI_PASSWORD);
}
 
void loop() {
  unsigned long now = millis();
  if (pumpOn && now - pumpStartedAt >= PUMP_RUN_MS) setPump(false);
  if (now - lastConfigAt >= 30000) { lastConfigAt = now; readConfig(); }
  if (now - lastSensorAt < 10000) { delay(20); return; }
  lastSensorAt = now;
 
  float temperature = dht.readTemperature();
  int soil = constrain(map(analogRead(SOIL_PIN), DRY_VALUE, WET_VALUE, 0, 100), 0, 100);
  if (!systemEnabled) { safeStop("remote-disabled"); return; }
  if (isnan(temperature)) { safeStop("sensor-error"); return; }
  if (fanOffAt >= fanOnAt) { safeStop("configuration-error"); return; }
 
  if (!fanOn && temperature >= fanOnAt) fanOn = true;
  if (fanOn && temperature <= fanOffAt) fanOn = false;
  setOutput(FAN_PIN, fanOn);
 
  bool cooldownReady = now - pumpStoppedAt >= PUMP_COOLDOWN_MS;
  if (!pumpOn && soil < wateringThreshold && cooldownReady) setPump(true);
 
  client.setData("greenhouse/temperature", String(temperature, 1));
  client.setData("greenhouse/soil-moisture", String(soil));
  client.setData("greenhouse/fan-status", fanOn ? "1" : "0");
  client.setData("greenhouse/pump-status", pumpOn ? "1" : "0");
  client.setData("greenhouse/status", "normal");
}

Commissioning

Validate sensors first, then test driver outputs with LEDs. Confirm hysteresis, five-second watering, one-minute cooldown, remote disable, and sensor-error shutdown before connecting loads. A field system also needs reservoir, flow, relay-feedback, and independent hardware protection.