Overview

The JSN-SR04T (and updated V2.0 / V3.0 / AJ-SR04M versions) is a waterproof ultrasonic distance ranging module designed for outdoor environmental monitoring, water tank level sensing, automotive reverse parking alarms, and industrial bin fill-level systems.

Consisting of a sealed IP68 waterproof transducer probe ($2.5\text{ meter}$ cable) connected to a driver board, it measures distances from $20\text{ cm}$ to $600\text{ cm}$ ($6.0\text{ meters}$). The JSN-SR04T V2.0/V3.0 features solder jumpers on the back of the PCB allowing operation in standard HC-SR04 Trigger/Echo mode, Automatic UART mode, or Low-Power Serial mode.

Quick reference

Pinout

Driver processing board 4-pin header:

Specifications

PCB Solder Jumper Modes (JSN-SR04T V2.0 / V3.0)

• Mode 0 (Default - Open Jumpers R27 & M1): HC-SR04 Compatible Mode. Send $10\ \mu\text{s}$ High pulse to Trig, measure High pulse width on Echo.
• Mode 1 (R27 soldered with $47\text{ k}\Omega$ or Short): Automatic UART Output. Sensor continuously outputs 4-byte serial telemetry at 9600 bps (0xFF, Data_H, Data_L, Checksum).
• Mode 2 (R27 soldered with $120\text{ k}\Omega$): Controlled UART Output. Send byte 0x55 over UART to request a single distance reading.

Speed of Sound Calculation Math (Mode 0)

$\text{Distance (cm)} = \frac{\text{Echo High Time } (\mu\text{s}) \times 0.0343}{2}$

$\text{Distance (cm)} = \frac{\text{Echo High Time } (\mu\text{s})}{58.3}$

Wiring (Mode 0 - HC-SR04 Mode)

Example (Mode 0 - Trigger / Echo Code)

const int trigPin = 5;
const int echoPin = 18;

void setup() {
  Serial.begin(115200);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  digitalWrite(trigPin, LOW);
}

void loop() {
  // Send 10us High pulse to Trigger pin
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Read Echo pulse width (timeout 35ms for ~6m range)
  long duration = pulseIn(echoPin, HIGH, 35000);
  
  if (duration == 0) {
    Serial.println("JSN-SR04T Out of range / No Echo received");
  } else {
    float distance_cm = duration / 58.3;
    float distance_m = distance_cm / 100.0;

    Serial.print("Water Level / Distance: ");
    Serial.print(distance_cm); Serial.print(" cm (");
    Serial.print(distance_m); Serial.println(" m)");
  }

  delay(500);
}

Common mistakes

• Attempting to measure distances under 20 cm: Because the JSN-SR04T uses a single piezoelectric transducer element for both transmitting and receiving (unlike the dual-cylinder HC-SR04), mechanical ring-down oscillations create a $20\text{ cm}$ blind zone. Objects closer than 20 cm return erroneous 20 cm readings.
• Submerging the processing driver PCB: Only the sealed transducer cylinder and cable are IP68 waterproof. The green processing driver circuit board must be housed in a dry enclosure.

Notes

• JSN-SR04T vs HC-SR04 vs AJ-SR04M: HC-SR04 uses 2 non-waterproof transducers ($2\text{cm}\dots 400\text{cm}$); JSN-SR04T uses 1 waterproof transducer ($20\text{cm}\dots 600\text{cm}$).