5. Water Tank Level Monitoring

Measure the distance from the tank top to the water surface, then map calibrated empty and full distances to a percentage.

Level: Intermediate · Time: 45 minutes

Requirements and wiring

Use an HC-SR04 for a dry prototype; prefer a protected or waterproof sensor in humid installations. Level-shift ECHO from 5 V to 3.3 V.

HC-SR04	ESP32
VCC / GND	5V / GND
TRIG	GPIO 5
ECHO	GPIO 18 through divider

EMPTY_DISTANCE_CM is the sensor-to-lowest-level distance; FULL_DISTANCE_CM is the sensor-to-highest-allowed-level distance.

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 TRIG_PIN = 5;
const int ECHO_PIN = 18;
const float EMPTY_DISTANCE_CM = 90.0;
const float FULL_DISTANCE_CM = 10.0;
 
PxServ client(PXSERV_API_KEY);
 
float readDistanceCm() {
  digitalWrite(TRIG_PIN, LOW); delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH); delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  unsigned long duration = pulseIn(ECHO_PIN, HIGH, 30000);
  return duration == 0 ? -1 : duration * 0.0343f / 2.0f;
}
 
void setup() {
  Serial.begin(115200);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  PxServ::connectWifi(WIFI_SSID, WIFI_PASSWORD);
}
 
void loop() {
  float distance = readDistanceCm();
  if (distance < 0) {
    client.setData("tank/sensor-status", "no-reading");
    delay(5000);
    return;
  }
 
  float level = (EMPTY_DISTANCE_CM - distance) * 100.0 /
                (EMPTY_DISTANCE_CM - FULL_DISTANCE_CM);
  level = constrain(level, 0.0f, 100.0f);
  String status = level < 20 ? "low" : level > 90 ? "high" : "normal";
 
  client.setData("tank/distance-cm", String(distance, 1));
  client.setData("tank/level-percent", String(level, 1));
  client.setData("tank/status", status);
  client.setData("tank/sensor-status", "normal");
  delay(10000);
}

Test and limits

Mount the sensor perpendicular to the surface and calibrate both endpoints. Do not rely on this prototype as the only overflow or pump safety; use independent physical level switches in a real installation.