2. Smart Plant Watering

Run a pump briefly when calibrated soil moisture falls below a threshold. A remote mode, maximum run time, and cooldown make the prototype safer and easier to observe.

Level: Intermediate · Time: 50 minutes

Safety and wiring

Use only a low-voltage DC mini pump. Never power it from an ESP32 pin. Use a suitable relay or MOSFET driver, external supply, shared GND, and inductive-load protection. Never switch mains voltage.

Part	ESP32
Soil sensor AOUT	GPIO 34
Soil sensor VCC / GND	3V3 / GND
Driver IN	GPIO 23
Driver GND	Common GND

The example assumes an active-low relay.

Complete sketch


#include <PxServ.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 SOIL_PIN = 34;
const int PUMP_PIN = 23;
const int DRY_VALUE = 3000;  // Calibrate
const int WET_VALUE = 1400;  // Calibrate
const int START_THRESHOLD = 35;
const unsigned long MAX_PUMP_MS = 5000;
const unsigned long COOLDOWN_MS = 30000;
 
PxServ client(PXSERV_API_KEY);
bool pumpRunning = false;
unsigned long pumpStartedAt = 0;
unsigned long lastPumpStoppedAt = 0;
unsigned long lastCycleAt = 0;
 
void setPump(bool enabled) {
  pumpRunning = enabled;
  digitalWrite(PUMP_PIN, enabled ? LOW : HIGH);
  client.setData("watering/pump-status", enabled ? "1" : "0");
  if (enabled) pumpStartedAt = millis();
  else lastPumpStoppedAt = millis();
}
 
void setup() {
  Serial.begin(115200);
  pinMode(PUMP_PIN, OUTPUT);
  digitalWrite(PUMP_PIN, HIGH);
  analogReadResolution(12);
  PxServ::connectWifi(WIFI_SSID, WIFI_PASSWORD);
}
 
void loop() {
  unsigned long now = millis();
  if (pumpRunning && now - pumpStartedAt >= MAX_PUMP_MS) setPump(false);
  if (now - lastCycleAt < 5000) { delay(20); return; }
  lastCycleAt = now;
 
  int raw = analogRead(SOIL_PIN);
  int moisture = constrain(map(raw, DRY_VALUE, WET_VALUE, 0, 100), 0, 100);
  client.setData("watering/moisture-percent", String(moisture));
 
  String mode = "automatic";
  PxServ::Callback modeResult = client.getData("watering/mode");
  if (modeResult.status == 200) mode = modeResult.data;
 
  bool requestPump = false;
  if (mode == "manual") {
    PxServ::Callback manual = client.getData("watering/manual-pump");
    requestPump = manual.status == 200 && manual.data == "1";
  } else {
    requestPump = moisture < START_THRESHOLD;
  }
 
  bool cooldownFinished = now - lastPumpStoppedAt >= COOLDOWN_MS;
  if (requestPump && !pumpRunning && cooldownFinished) setPump(true);
  if (!requestPump && pumpRunning) setPump(false);
}

Commissioning

Test with only the relay indicator first. Confirm calibration, manual control, the five-second shutoff, and cooldown before connecting the pump. A real system also needs reservoir level, leak/flow detection, and a hardware cutoff.