This project builds an autonomous water tank inlet controller using an ESP32 to manage a 12V solenoid valve with dual float-switch safety. The system monitors a main float to detect when the tank reaches its normal full level, while an emergency high-level float provides backup protection. The guide includes a complete wiring diagram, parts list, and firmware that implements debounced float sensing, opto-isolated safety monitoring, and fail-safe valve control logic.
Builders will receive step-by-step assembly instructions covering valve mounting, float placement, controller box installation, and the protected 12-volt valve circuit. The firmware excerpt demonstrates how the ESP32 reads float states, validates safety power availability, and drives the MOSFET gate to control the normally-closed solenoid. All safety states are tested before plumbing connection to ensure reliable autonomous operation.
Wiring diagram
Gather all the parts
Assemble it in 7 steps
1. Fit the water valve safely
Turn off the building water at the existing stop-cock, open a nearby tap to release pressure, then have a qualified plumber replace the exposed 1/2-inch BSP section with the 12 V normally-closed valve. Follow the flow arrow stamped on the valve body. Keep the valve itself in the wet plumbing area, but make every electrical join above splash level and inside a sealed junction box.
- The valve is closed when it has no electrical power, so this is the safe position while fitting it.
- Use thread sealant appropriate for potable-water plumbing.
- Do not work on a pressurized pipe; a loosened fitting can spray water and cause property damage.
- Do not install the ESP32, power adapter, or open wire joins in the bathroom splash zone.
2. Mount the two tank floats
Mount main_float at the normal full-water line and rotate or test it so its two wires connect together when water reaches that line. Mount backup_float a little higher and orient it so its two wires connect together below that emergency level, then separate when water rises to the emergency level. Run both low-voltage float cables back to the dry controller enclosure using protected cable.
- Before final mounting, use a multimeter to check each float while you move it by hand; float switch orientation changes whether its contact is open or closed.
- Leave enough cable slack to remove a float for cleaning.
- The backup float must open at high water; if it is reversed, it cannot remove power during an overflow.
- Keep float cables clear of the tank lid and any sharp edge that could cut their insulation.
3. Mount the dry controller box
Fit a sealed plastic enclosure in a dry, reachable place away from shower spray and outside the concealed-pipe wall. Mount the ESP32, the 12 V adapter connection, buck converter, fuse holder, MOSFET board parts, LED, and manual_off switch inside or on this enclosure. Bring the 12 V adapter lead into the enclosure through a strain-relief cable gland.
- Label the switch positions clearly: OPEN ENABLED for the position that connects COM to NO1, and OFF for the open position.
- Set the buck converter output to 5.0 V with a multimeter before connecting it to the ESP32 VIN pin.
- Do not put mains-voltage wiring inside the low-voltage enclosure unless a qualified electrician provides a properly rated separate compartment.
- A loose 12 V wire can heat up or damage parts; use screw terminals or crimped connectors, not twisted bare wire.
4. Build the protected 12-volt valve path
From power_adapter +12V, wire to valve_fuse IN, then valve_fuse OUT to manual_off COM. Wire manual_off NO1 to backup_float SAFETY_IN, and backup_float SAFETY_OUT to valve VALVE+. Wire valve VALVE- to mosfet Drain (D), and mosfet Source (S) to the common GND rail. Place flyback_diode across the valve: its striped CATHODE end goes to valve VALVE+, and its unstriped ANODE end goes to valve VALVE-.
- This chain means the switch OFF position or a high backup float removes 12 V from the valve even if the ESP32 is faulty.
- The diode goes directly across the valve wires, not in series with the valve.
- Do not reverse the flyback diode; reversed diode wiring can create a short circuit when the valve is powered.
- Use a fuse value only large enough for the valve's normal label current; do not bypass the fuse.
5. Wire the ESP32 control and indicator
Make one shared low-voltage GND rail: power_adapter GND, buck VIN-, buck VOUT-, ESP32 GND, and mosfet Source all join there. Wire buck VIN+ to power_adapter +12V, then buck VOUT+ to ESP32 VIN (power) and buck VOUT- to ESP32 GND (ground). Wire main_float GND to ESP32 GND (ground) and main_float SIGNAL to GPIO32 (level signal). Wire GPIO25 to gate_resistor A (control), gate_resistor B to mosfet Gate (control), and gate_pulldown from the MOSFET gate to GND (keeps the valve closed while the ESP32 starts). Wire GPIO26 to led_resistor A, led_resistor B to the LED long leg, and the LED short leg to GND (open-valve light).
- The LED's long leg is positive; it lights only when the ESP32 commands the valve open.
- The 10 kΩ resistor is important: it holds the MOSFET off during reset, so the valve stays closed until the ESP32 has read the tank level.
- Do not connect the 12 V valve wire to any ESP32 GPIO; ESP32 pins accept only 3.3 V logic signals and can be destroyed by 12 V.
- Make sure the LED has its 220 Ω resistor in series; connecting an LED directly to GPIO26 can damage the LED or board.
6. Connect the safety status monitor
Wire safety_sense IN+ to valve VALVE+ (the final switched 12 V at the valve), and safety_sense IN- to the common GND rail. Wire safety_sense VCC to ESP32 3V3 (power), safety_sense GND to ESP32 GND (ground), and safety_sense OUT to GPIO33 (status signal). This monitor lets the ESP32 see when the final valve supply is unavailable.
- With the manual switch OFF or the backup float high, the monitor reports that valve power is unavailable; this is expected.
- Use the input/output isolation arrangement printed on your exact opto module; terminals vary between module brands.
- Check the opto module really accepts a 12 V input and provides a 3.3 V-safe output before connecting it to GPIO33.
- Never share an unknown module output with 12 V; only its marked 3.3 V logic OUT terminal goes to the ESP32.
7. Test every safe state before plumbing use
With the valve plumbing complete and the tank floats accessible, plug in the 12 V adapter and press Deploy in Schematik. First set the manual_off switch to OFF: the valve must remain closed and the LED must be off. Then enable the switch with the main float in its low-water position: the LED should turn on and the valve should open. Lift the main float to its full position: the LED should turn off and the valve should close. Return the main float low, then lift the backup float: the valve must close even though the main float asks it to open. Finally, remove adapter power: the valve and LED must turn off and the valve must close.
- A faint click from the solenoid and the LED changing state are useful first checks before allowing water pressure through.
- Repeat the backup-float test periodically; it is the independent overflow protection.
- If any test produces the opposite result, unplug the 12 V adapter immediately and correct the float orientation or wiring before leaving the system connected.
- Do not rely on this system until both the normal-full and backup-high tests close the valve reliably.
Review all connections
1. Connections between "main_float" and "ESP32"
2. Connections between "backup_float" and "ESP32"
3. Connections between "valve" and "ESP32"
4. Connections between "mosfet" and "ESP32"
5. Connections between "power_adapter" and "ESP32"
6. Connections between "buck" and "ESP32"
7. Connections between "valve_led" and "ESP32"
8. Connections between "flyback_diode" and "ESP32"
9. Connections between "gate_resistor" and "ESP32"
10. Connections between "gate_pulldown" and "ESP32"
11. Connections between "safety_sense" and "ESP32"
12. Connections between "valve_fuse" and "ESP32"
13. Connections between "led_resistor" and "ESP32"
Deploy the firmware
#include <Arduino.h>
// Autonomous storage-tank inlet controller for ESP32 DevKit v1.
// GPIO25 drives the low-side MOSFET: HIGH energizes the normally-closed valve.
// The normal float is wired between GPIO32 and GND. With INPUT_PULLUP,
// LOW means the tank has reached the normal full level.
// The isolated safety monitor is HIGH only while 12 V is present at VALVE+.
// Forward declarations
bool tankIsFullFromRawInput();
bool safetyPowerAvailable();
void applyValveState();
constexpr int VALVE_GATE_PIN = 25;
constexpr int VALVE_LED_PIN = 26;
constexpr int MAIN_FLOAT_PIN = 32;
constexpr int SAFETY_POWER_PIN = 33;
constexpr unsigned long DEBOUNCE_MS = 80;
bool rawMainFull = false;
bool stableMainFull = false;
unsigned long lastMainChangeMs = 0;
bool tankIsFullFromRawInput() {
// Float contact closed to GND = water has reached the normal full line.
return digitalRead(MAIN_FLOAT_PIN) == LOW;
}
bool safetyPowerAvailable() {
// The opto module's stated logic is HIGH while its 12 V input is powered.
// LOW means the manual cutoff is off, the backup float has opened, or
// the 12 V safety chain is otherwise interrupted.
return digitalRead(SAFETY_POWER_PIN) == HIGH;
}
void applyValveState() {
const bool safetyOk = safetyPowerAvailable();
const bool shouldOpenValve = !stableMainFull && safetyOk;
// A LOW gate keeps the normally-closed valve de-energized and closed.
digitalWrite(VALVE_GATE_PIN, shouldOpenValve ? HIGH : LOW);
digitalWrite(VALVE_LED_PIN, shouldOpenValve ? HIGH : LOW);
}
void setup() {
// Set outputs LOW before reading inputs, so reset/boot cannot command flow.
pinMode(VALVE_GATE_PIN, OUTPUT);
pinMode(VALVE_LED_PIN, OUTPUT);
digitalWrite(VALVE_GATE_PIN, LOW);
digitalWrite(VALVE_LED_PIN, LOW);
pinMode(MAIN_FLOAT_PIN, INPUT_PULLUP);
pinMode(SAFETY_POWER_PIN, INPUT_PULLUP);
// Read the actual installed float position now; no float movement is needed
// after a reboot or power restoration.
rawMainFull = tankIsFullFromRawInput();
stableMainFull = rawMainFull;
lastMainChangeMs = millis();
applyValveState();
}
void loop() {
const unsigned long now = millis();
const bool rawNow = tankIsFullFromRawInput();
if (rawNow != rawMainFull) {
rawMainFull = rawNow;
lastMainChangeMs = now;
}
// Ignore brief contact chatter, but react to an already-present level at boot.
if (rawMainFull != stableMainFull && now - lastMainChangeMs >= DEBOUNCE_MS) {
stableMainFull = rawMainFull;
}
// The backup cut-off and manual switch are sampled every pass. Even if the
// ESP32 failed, their series 12 V path still removes coil power directly.
applyValveState();
delay(10);
}Remix this project
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Open a full copy of this project in your own Schematik workspace, diagram, code, parts, and assembly steps included. Swap the sensor, add features, or redesign the whole thing with AI. The author's original stays untouched.
