Water Hazard Prevention System, a ESP32 project

This water hazard prevention system uses an ESP32 to monitor water levels and distance, automatically deploying physical barriers and debris removal when flooding is detected. Built around dual float switches and an HC-SR04 ultrasonic sensor, the system triggers a high-torque barrier motor and a scraper motor via an L298N motor driver, while a relay module controls a 12 V warning light and siren.

The guide provides a complete wiring diagram, detailed parts list, and step-by-step assembly instructions for integrating the 24 V buck converter, solar and hydro power sources with battery backup, and all sensor and actuator connections. Included firmware implements hazard detection logic, motor timing control, and alert activation—ready to load onto the ESP32 DevKit v1.

Wiring diagram

Gather all the parts

Qty	Component
1	24v Buck Converter Set output to 5.0 V before connecting logic LM2596-based adjustable step-down buck converter module. Commonly used to regulate a higher battery rail, such as a 2S 18650 pack, down to 5V for Arduino logic. It is a regulator, not a charger or battery protection board.
1	DFRobot MDV 2x2A DC Motor Controller (L298N) L298N dual H-bridge motor driver carrier. 2A continuous per channel, 5-46V motor supply, ~1.8V dropout (BJT-based, hot at high currents). Drives 2 brushed DC motors or 1 bipolar stepper. Pair with PWM on EN pins for speed control.
1	HC-SR04 Ultrasonic distance measurement sensor
1	5 V Optocoupled Single-Channel Relay Module Optocoupled 5 V relay board that lets the Arduino switch the 12 V warning light and siren.
1	Float Switch Low water level Float switch (liquid level switch): a buoyant float carries a magnet that actuates a hermetically sealed reed contact as the liquid rises or falls past the mounting point. Two-wire SPST dry contact (normally-open or normally-closed) with no power supply of its own -- wired like a push-button on a GPIO with INPUT_PULLUP, where open/closed indicates the level is above/below the float. Common for pump on/off control, tank full/empty detection, and sump alarms.
1	Float Switch High water level Float switch (liquid level switch): a buoyant float carries a magnet that actuates a hermetically sealed reed contact as the liquid rises or falls past the mounting point. Two-wire SPST dry contact (normally-open or normally-closed) with no power supply of its own -- wired like a push-button on a GPIO with INPUT_PULLUP, where open/closed indicates the level is above/below the float. Common for pump on/off control, tank full/empty detection, and sump alarms.
1	12 V SLA Battery Sealed lead-acid battery that stores energy for the hazard-prevention system.
1	12 V 10 W Solar Panel Solar panel that supplies charging energy in sunlight.
1	12 V 10 W DC Micro-Hydro Generator DC micro-hydro generator that supplies charging energy from flowing water.
1	12 V Solar/Hydro Charge Controller Charge controller with separate solar and auxiliary DC inputs for safely charging the 12 V battery.
1	12 V High-Torque DC Gear Motor Brushed gear motor that raises and lowers the barrier gate.
1	12 V Mini DC Gear Motor Brushed gear motor that drives the debris scraper belt.
1	12 V Warning Light Flasher and Siren Combined 12 V visual and audible warning unit switched by the relay.
1	5 A Automotive Blade Fuse Replaceable fuse that protects the 12 V load branch from a wiring fault.
1	1 A Inline Fuse Replaceable fuse that protects the low-current logic supply branch.
1	SMBJ18A 18 V TVS Diode Surge clamp placed across the 12 V bus to protect electronics from motor and cable transients.
1	470 uF 25 V Electrolytic Capacitor Bulk capacitor that absorbs short 12 V motor-current spikes near the motor driver.
1	220 uF 10 V Electrolytic Capacitor Bulk capacitor that smooths the 5 V logic rail near the controller.
1	100 nF Ceramic Capacitor Small ceramic capacitor that filters high-frequency noise on the 5 V logic rail.
1	100 nF Ceramic Motor Suppression Capacitor Capacitor connected directly across the barrier motor terminals to reduce brush noise.
1	100 nF Ceramic Motor Suppression Capacitor Capacitor connected directly across the scraper motor terminals to reduce brush noise.
1	10 kΩ Resistor (HC-SR04 Echo Divider, Upper) This resistor reduces the ultrasonic sensor's 5 V echo signal before it reaches the ESP32.
1	18 kΩ Resistor (HC-SR04 Echo Divider, Lower) This resistor completes the ultrasonic-sensor voltage divider and keeps the ESP32 input safely below 3.3 V.
1	2N2222A NPN Transistor This transistor lets the ESP32 safely switch the 5 V relay module input.
1	1 kΩ Resistor (Relay Driver Base) This resistor limits control current from the ESP32 into the relay-driver transistor.

Assemble it in 7 steps

1. Build the fused power section

Mount CHARGER1, F1_load, F2_logic, D1_tvs, C1_12v_bulk, and U2_lm2596 inside a covered power enclosure. Keep the thick battery and motor wires away from the thin ESP32 and sensor wires so motor noise is less likely to disturb the controller.

A 12 V SLA battery can melt thin wire or start a fire during a short circuit, so put both fuses close to the charge-controller load output.
Set the buck converter to exactly 5.0 V with a meter before connecting the ESP32 or any 5 V module; more than 5 V can damage them.

2. Connect the sources and battery

With the battery disconnected, connect PV1_solar positive to CHARGER1 SOLAR+ and negative to SOLAR-. Connect GEN1_hydro positive to AUX+ and negative to AUX-. Connect BT1_12v_sla BAT+ to BAT+ and BAT- to BAT-.

The hydro generator must provide regulated DC compatible with the controller AUX input; do not connect raw AC generator wires.
Do not reverse the battery wires — reversed battery power can permanently damage the controller and connected electronics.

3. Make the 12 V and 5 V rails

Connect CHARGER1 LOAD+ through F1_load to the 12 V bus and LOAD- to GND_COMMON. Connect D1_tvs cathode to the 12 V bus and anode to GND_COMMON. Feed F2_logic from the 12 V bus into U2_lm2596 VIN+. Connect VIN- to GND_COMMON, VOUT+ to the 5 V rail, and VOUT- to GND_COMMON. Put C1_12v_bulk across 12 V and ground, then C2_5v_bulk and C3_5v_ceramic across 5 V and ground.

The striped side of each electrolytic capacitor goes to GND_COMMON; reversed capacitors can burst.

4. Wire the ESP32 water inputs

Connect the ESP32 DevKit 5V/VIN pin to the 5 V rail and a GND pin to GND_COMMON. Connect each float switch's GND terminal to GND_COMMON: S1_low_float SIGNAL goes to GPIO32 (signal) and S2_high_float SIGNAL goes to GPIO33 (signal). Connect U4_hcsr04 VCC to 5 V (power), GND to GND_COMMON (ground), and TRIG to GPIO18 (signal). Connect HC-SR04 ECHO to R1_echo_top pin 1; connect R1 pin 2 to GPIO19 and R2_echo_bottom pin 1; connect R2 pin 2 to GND_COMMON.

Never connect the HC-SR04 ECHO pin straight to an ESP32 pin — its 5 V pulse can damage the 3.3 V ESP32 input.
If a float reports the opposite water state, turn the float over or invert that input in the firmware.

5. Wire the motor driver and motors

Connect U3_l298n VS to the 12 V bus (power), GND to GND_COMMON (ground), and 5V, ENA, and ENB to the 5 V rail. Connect IN1 to GPIO21, IN2 to GPIO22, IN3 to GPIO23, and IN4 to GPIO25 (signals). Connect OUT1 and OUT2 to M1_barrier M+ and M-; connect OUT3 and OUT4 to M2_scraper M+ and M-. Solder C4_m1_suppress directly across M1's two terminals and C5_m2_suppress across M2's two terminals.

Check the barrier motor's stall current: an L298N may overheat if the motor needs more current than the module can continuously supply.
Keep hands clear of the gate and scraper during the first powered test because a detected hazard can move them.

6. Add the protected warning relay control

Connect R3_relay_base pin 1 to ESP32 GPIO26 (signal) and pin 2 to Q1_relay_driver B. Connect Q1 C to K1_relay IN and Q1 E to GND_COMMON. Connect K1 VCC to 5 V (power) and K1 GND to GND_COMMON (ground). Connect K1 COM to the 12 V bus, K1 NO to ALERT1 V+, and ALERT1 GND to GND_COMMON.

Do not connect ESP32 GPIO26 directly to the 5 V relay IN pin — the transistor circuit protects the 3.3 V controller.
Do not touch exposed relay contacts or warning-load wiring while the battery is connected; a short can make wires dangerously hot.

7. Inspect before applying power

Check that every ground wire returns to GND_COMMON and measure the 5 V rail one final time. With motors mechanically unloaded, power the ESP32 from the regulated 5 V rail, then test the two floats and ultrasonic sensor before allowing the barrier mechanism to move.

The ESP32 uses its USB connection for flashing, but the motors and 5 V modules still use the regulated supply.

Review all connections

1. Connections between "PV1_solar" and "ESP32"

Function	PV1_solar	ESP32
`power`	PV+ → 12 V Solar/Hydro Charge Controller SOLAR+	EXT
`ground`	PV-	GND

2. Connections between "GEN1_hydro" and "ESP32"

Function	GEN1_hydro	ESP32
`power`	GEN+ → 12 V Solar/Hydro Charge Controller AUX+	EXT
`ground`	GEN-	GND

3. Connections between "CHARGER1" and "ESP32"

Function	CHARGER1	ESP32
`ground`	SOLAR-	GND
`ground`	AUX-	GND
`power`	BAT+ → 12 V SLA Battery BAT+	EXT
`ground`	BAT-	GND
`power`	LOAD+ → 5 A Automotive Blade Fuse IN	EXT
`ground`	LOAD-	GND

4. Connections between "BT1_12v_sla" and "ESP32"

Function	BT1_12v_sla	ESP32
`ground`	BAT-	GND

5. Connections between "F1_load" and "ESP32"

Function	F1_load	ESP32
`power`	OUT	VIN

6. Connections between "D1_tvs" and "ESP32"

Function	D1_tvs	ESP32
`power`	CATHODE	VIN
`ground`	ANODE	GND

7. Connections between "C1_12v_bulk" and "ESP32"

Function	C1_12v_bulk	ESP32
`power`	+	VIN
`ground`	-	GND

8. Connections between "F2_logic" and "ESP32"

Function	F2_logic	ESP32
`power`	IN	VIN
`power`	OUT → 24v Buck Converter VIN+	EXT

9. Connections between "U2_lm2596" and "ESP32"

Function	U2_lm2596	ESP32
`ground`	VIN-	GND
`power`	VOUT+	5V
`ground`	VOUT-	GND

10. Connections between "C2_5v_bulk" and "ESP32"

Function	C2_5v_bulk	ESP32
`power`	+	5V
`ground`	-	GND

11. Connections between "C3_5v_ceramic" and "ESP32"

Function	C3_5v_ceramic	ESP32
`power`	1	5V
`ground`	2	GND

12. Connections between "U3_l298n" and "ESP32"

Function	U3_l298n	ESP32
`power`	VS	VIN
`ground`	GND	GND
`power`	5V	5V
`power`	ENA	5V
`power`	ENB	5V
`output`	OUT1 → 12 V High-Torque DC Gear Motor M+	EXT
`output`	OUT2 → 12 V High-Torque DC Gear Motor M-	EXT
`output`	OUT3 → 12 V Mini DC Gear Motor M+	EXT
`output`	OUT4 → 12 V Mini DC Gear Motor M-	EXT
`digital`	IN1	GPIO 21
`digital`	IN2	GPIO 22
`digital`	IN3	GPIO 23
`digital`	IN4	GPIO 25

13. Connections between "C4_m1_suppress" and "ESP32"

Function	C4_m1_suppress	ESP32
`power`	1 → 12 V High-Torque DC Gear Motor M+	EXT
`power`	2 → 12 V High-Torque DC Gear Motor M-	EXT

14. Connections between "C5_m2_suppress" and "ESP32"

Function	C5_m2_suppress	ESP32
`power`	1 → 12 V Mini DC Gear Motor M+	EXT
`power`	2 → 12 V Mini DC Gear Motor M-	EXT

15. Connections between "U4_hcsr04" and "ESP32"

Function	U4_hcsr04	ESP32
`power`	VCC	5V
`ground`	GND	GND
`digital`	TRIG	GPIO 18
`digital`	ECHO → 10 kΩ Resistor (HC-SR04 Echo Divider, Upper) 1	EXT

16. Connections between "S1_low_float" and "ESP32"

Function	S1_low_float	ESP32
`ground`	GND	GND
`data`	SIGNAL	GPIO 32

17. Connections between "S2_high_float" and "ESP32"

Function	S2_high_float	ESP32
`ground`	GND	GND
`data`	SIGNAL	GPIO 33

18. Connections between "K1_relay" and "ESP32"

Function	K1_relay	ESP32
`power`	VCC	5V
`ground`	GND	GND
`power`	COM	VIN
`power`	NO → 12 V Warning Light Flasher and Siren V+	EXT

19. Connections between "ALERT1" and "ESP32"

Function	ALERT1	ESP32
`ground`	GND	GND

20. Connections between "R1_echo_top" and "ESP32"

Function	R1_echo_top	ESP32
`data`	2	GPIO 19

21. Connections between "R2_echo_bottom" and "ESP32"

Function	R2_echo_bottom	ESP32
`ground`	2	GND
`data`	1 → 10 kΩ Resistor (HC-SR04 Echo Divider, Upper) 2	EXT

22. Connections between "R3_relay_base" and "ESP32"

Function	R3_relay_base	ESP32
`data`	1	GPIO 26
`data`	2 → 2N2222A NPN Transistor B	EXT

23. Connections between "Q1_relay_driver" and "ESP32"

Function	Q1_relay_driver	ESP32
`digital`	C → 5 V Optocoupled Single-Channel Relay Module IN	EXT
`ground`	E	GND

Deploy the firmware

main.cppOpen in Schematik

// D.P.W.H. AI - flood hazard controller for ESP32 DevKit v1.
// Float switches connect their input to GND and use the ESP32 internal pull-ups.
// HC-SR04 ECHO passes through the 10 kΩ / 18 kΩ divider before GPIO19.

const uint8_t TRIG_PIN = 18;
const uint8_t ECHO_PIN = 19;
const uint8_t BARRIER_UP_PIN = 21;
const uint8_t BARRIER_DOWN_PIN = 22;
const uint8_t SCRAPER_START_PIN = 23;
const uint8_t SCRAPER_DIRECTION_PIN = 25;
const uint8_t RELAY_PIN = 26;
const uint8_t LOW_FLOAT_PIN = 32;
const uint8_t HIGH_FLOAT_PIN = 33;

// GPIO26 HIGH turns on Q1, pulling the relay module's active-low IN pin down.
const bool RELAY_ACTIVE_LOW = false;
const unsigned long SAMPLE_INTERVAL_MS = 250UL;
const unsigned long BARRIER_MAX_RUN_MS = 3000UL;
const unsigned long SCRAPER_ON_MS = 2000UL;
const unsigned long SCRAPER_PERIOD_MS = 10000UL;
const int HAZARD_DISTANCE_CM = 25;

bool hazardLatched = false;
bool barrierRunning = false;
unsigned long barrierStartMs = 0;
unsigned long lastSampleMs = 0;

void stopBarrier() {
  digitalWrite(BARRIER_UP_PIN, LOW);
  digitalWrite(BARRIER_DOWN_PIN, LOW);
  barrierRunning = false;
}

void raiseBarrierForMaximumTime() {
  // Never drive both L298N direction inputs high.
  digitalWrite(BARRIER_DOWN_PIN, LOW);
  digitalWrite(BARRIER_UP_PIN, HIGH);
  barrierStartMs = millis();
  barrierRunning = true;
}

void stopScraper() {
  digitalWrite(SCRAPER_START_PIN, LOW);
  digitalWrite(SCRAPER_DIRECTION_PIN, LOW);
}

void setAlert(bool on) {
  digitalWrite(RELAY_PIN, (on == RELAY_ACTIVE_LOW) ? LOW : HIGH);
}

int readDistanceCm() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  unsigned long durationUs = pulseIn(ECHO_PIN, HIGH, 30000UL);
  if (durationUs == 0) return -1;
  return (int)(durationUs / 58UL);
}

void setup() {
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  pinMode(BARRIER_UP_PIN, OUTPUT);
  pinMode(BARRIER_DOWN_PIN, OUTPUT);
  pinMode(SCRAPER_START_PIN, OUTPUT);
  pinMode(SCRAPER_DIRECTION_PIN, OUTPUT);
  pinMode(RELAY_PIN, OUTPUT);
  pinMode(LOW_FLOAT_PIN, INPUT_PULLUP);
  pinMode(HIGH_FLOAT_PIN, INPUT_PULLUP);

  stopBarrier();
  stopScraper();
  setAlert(false);
  Serial.begin(9600);
}

void loop() {
  const unsigned long now = millis();

  if (barrierRunning && (now - barrierStartMs >= BARRIER_MAX_RUN_MS)) {
    stopBarrier();
  }

  if (now - lastSampleMs >= SAMPLE_INTERVAL_MS) {
    lastSampleMs = now;
    const bool lowWaterDetected = (digitalRead(LOW_FLOAT_PIN) == LOW);
    const bool highWaterDetected = (digitalRead(HIGH_FLOAT_PIN) == LOW);
    const int distanceCm = readDistanceCm();
    const bool closeWaterDetected = (distanceCm > 0 && distanceCm <= HAZARD_DISTANCE_CM);
    const bool hazardNow = highWaterDetected || closeWaterDetected;

    setAlert(hazardNow);

    if (hazardNow && !hazardLatched) {
      raiseBarrierForMaximumTime();
    }
    hazardLatched = hazardNow;

    // Pulse the scraper rather than leaving a water-exposed motor running continuously.
    if (hazardNow && (now % SCRAPER_PERIOD_MS) < SCRAPER_ON_MS) {
      digitalWrite(SCRAPER_DIRECTION_PIN, LOW);
      digitalWrite(SCRAPER_START_PIN, HIGH);
    } else {
      stopScraper();
    }

    Serial.print("low_float=");
    Serial.print(lowWaterDetected);
    Serial.print(" high_float=");
    Serial.print(highWaterDetected);
    Serial.print(" distance_cm=");
    Serial.print(distanceCm);
    Serial.print(" hazard=");
    Serial.println(hazardNow);
  }

  delay(5);
}