The JSN-SR04T is a waterproof ultrasonic distance measurement module that detects the range to an object by timing how long it takes an ultrasonic pulse to travel out, reflect off a surface, and return. Unlike standard ultrasonic modules, its sensing transducer is sealed and mounted on a cable separate from the control board, allowing the actual measuring element to be placed in wet or outdoor environments while the electronics stay protected.
This makes the JSN-SR04T ideal for applications such as liquid level sensing, outdoor parking sensors, rainwater tank monitoring, robotics obstacle avoidance, and any project requiring distance measurement in harsh or wet conditions. Its waterproof transducer, long measurement range, and drop-in pin compatibility with the standard HC-SR04 have made it a popular choice for outdoor and industrial maker projects.
What is JSN-SR04T?
The JSN-SR04T module ships in two separate parts: a small waterproof transducer (the sensing element, sealed for outdoor or wet use) connected via a cable, and a separate control board that handles signal generation and timing. This is the key difference from a standard ultrasonic module — the transducer can be mounted through a wall or panel into a wet environment while the control board itself stays in a dry enclosure.
Unlike the standard HC-SR04, which uses two separate transducers (one transmitter, one receiver), the JSN-SR04T uses a single waterproof transducer that serves as both transmitter and receiver. The breakout control board uses the exact same 4-pin layout as the HC-SR04, so in many designs it can be used as a drop-in replacement, just with the sensing element relocated to the end of a cable.
Version note: Several hardware revisions of this module exist (commonly labeled v1.0, v2.0, v3.0), with differing maximum range, minimum range, and onboard configuration options (such as a solder jumper for switching output mode). Always check the silkscreen or labeling on your specific board, since electrical behavior can vary slightly between revisions.
JSN-SR04T overview
| Parameter | Value |
|---|---|
| Sensor Type | Waterproof Ultrasonic Distance Sensor |
| Transducer Type | Single transducer (TX/RX combined) |
| Supply Voltage | 4.5V – 5.5V (5V typical) |
| Operating Current | Up to 30mA |
| Measurement Range | ~25cm – 450cm (up to 600cm on some versions) |
| Resolution | ~0.5cm (model dependent) |
| Trigger Pulse Width | 10–15µs |
| Ultrasonic Frequency | 40kHz |
| Output Signal | Echo pulse (TTL) or serial UART (mode dependent) |
| Cable Length (transducer) | ~2.5m typical |
| Pin Compatibility | Same 4-pin layout as HC-SR04 |
| Compatible Boards | Arduino, ESP32, Raspberry Pi |
Pinout
The JSN-SR04T breakout board has the same 4-pin layout as the standard HC-SR04, making it easy to swap into existing projects. The transducer itself connects to the board via a separate cable and connector on the back.
4-pin pinout
| Pin | Name | Type | Description |
|---|---|---|---|
| 1 | GND | Power | Ground connection |
| 2 | Echo | Output | Trigger input — held HIGH for ~10–15µs to start a measurement |
| 3 | Trig | Input | Echo output — goes HIGH for a duration proportional to the time taken for the ultrasonic wave to return |
| 4 | VCC | Power | Positive supply — typically 5V |
Mode jumper (select revisions): Some hardware versions include a solder jumper or resistor pad on the control board that switches the module between standard Trig/Echo mode and an automatic serial output mode, where the module continuously transmits distance readings as a TTL serial value every 100ms in millimeters, without needing a trigger pulse.
Working principle
To start a measurement, the Trig pin is held HIGH for roughly 10–15µs and then released. This causes the transducer to emit a burst of eight ultrasonic pulses at a frequency of 40kHz. These pulses travel outward, reflect off the nearest object in their path, and return to the same transducer, which now acts as a receiver.
Once the reflected wave is detected, the Echo pin goes HIGH for a duration equal to the time it took the wave to travel out and back. The host microcontroller measures how long Echo stays HIGH, and converts that time into a distance using the standard speed-of-sound calculation — distance equals time multiplied by the speed of sound, divided by two to account for the round trip.
Cycle timing: A new measurement should not be triggered again until the previous echo has fully faded out — the recommended minimum cycle period between triggers is around 50ms, to avoid one measurement’s echo interfering with the next.
No-object behavior: If no obstacle is detected within range, the Echo pin will still output a long HIGH pulse (on the order of tens of milliseconds) representing the maximum timeout, rather than staying permanently low — this allows the host to distinguish “no object detected” from a sensor fault.
JSN-SR04T Module Construction
The JSN-SR04T Waterproof Ultrasonic Sensor is designed for reliable distance measurement in harsh environments. It consists of a waterproof ultrasonic transducer and a dedicated control board that processes the transmitted and received ultrasonic signals.
STM8 Microcontroller: The STM8 microcontroller serves as the brain of the sensor module. It generates the trigger pulses, measures the echo return time, calculates the distance, and manages communication with external microcontrollers such as Arduino, ESP32, and Raspberry Pi.
LMV324 Operational Amplifier: The LMV324 operational amplifier processes the weak echo signals received from the ultrasonic transducer. It amplifies and conditions these signals, enabling accurate echo detection and distance measurement.
Driver Circuit (Inductor/Transformer Core): The driver circuit includes an inductor or transformer core that helps generate the high-voltage pulse required to excite the ultrasonic transducer. This allows the sensor to produce strong ultrasonic waves for long-range detection.
R27 Configuration Resistor: The R27 component is a configuration resistor or solder bridge used for factory calibration and circuit configuration. Its specific function may vary depending on the board revision.
Ultrasonic Unit Connector: The ultrasonic unit connector links the waterproof transducer to the control board. It carries both the transmitted ultrasonic pulse and the received echo signal between the transducer and the signal-processing circuitry.
Waterproof Ultrasonic Transducer: Unlike the HC-SR04, which uses separate transmitter and receiver transducers, the JSN-SR04T uses a single waterproof ultrasonic transducer for both transmitting and receiving 40 kHz ultrasonic waves. Its sealed construction protects it from water, moisture, and dust, making it suitable for outdoor applications.
Specifications
| Parameter | Value |
|---|---|
| Supply Voltage | 4.5V – 5.5V (5V typical) |
| Operating Current | Up to 30mA |
| Measurement Range | 25cm – 450cm (up to 600cm, version dependent) |
| Resolution | ~0.5cm |
| Accuracy | Up to ±3mm on some hardware revisions |
| Trigger Pulse Width | 10–15µs (active HIGH) |
| Ultrasonic Frequency | 40kHz |
| Recommended Cycle Period | ≥50ms between triggers |
| Output Modes | Trig/Echo pulse, or automatic serial (model dependent) |
| Serial Output Rate | ~100ms cycle, value in mm (where supported) |
| Transducer Cable Length | ~2.5m typical |
| Pin Layout | 4-pin, HC-SR04 compatible |
| Waterproofing | Transducer only — control board is not waterproof |
Helpful Resources
- Download the datasheet: here
- JSN-SR04T with Arduino
- JSN-SR04T with ESP32
- JSN-SR04T with Raspberry Pi