The JSN-SR04T waterproof ultrasonic sensor consists of a waterproof ultrasonic transducer (combined transmitter and receiver) and a separate control board. The control board drives the transducer and provides a standard interface for connection to a microcontroller, allowing users to trigger measurements and read distance data. The sensor measures distance using high-frequency, inaudible ultrasonic waves. When triggered, the module emits a burst of ultrasonic pulses and listens for the reflected echo from a target within range. The distance is calculated by measuring the time between transmission and reception of the ultrasonic signal.
Features / Specs
- Manufacturer: Generic
- Model: AJ-SR04M (JSN-SR04T Compatible)
- Operating Voltage Range: 3.0V – 5.0VDC
- Operating Current: < 8mA
- Ultrasonic Transceiver Frequency: 40kHz
- Measuring Range: ~(20 – 600cm)
- Accuracy (Long Range): ± 1cm
- Resolution: 1mm
- Detection Angle: 75°
- Input Trigger: TTL pulse ≥ 10µs / Serial command: 0x55
- Output Signal: Pulse width voltage signal (TTL) / UART serial output (depending on mode setting)
- Operating Temperature Range: -20℃ to +70℃
- Cable Length: ~2.2 Meters
- PCB Dimensions: ~(41.3mm x 28.5mm x 17.8mm)
- Mounting Hole Diameter: ~2.6mm
- Mounting Hole Spacing (Center to Center): ~(35.8mm x 23.9mm)
Operation Overview
The JSN-SR04T clone ultrasonic sensor supports three selectable operating modes, determined by the value of the SMD resistor at position “R19” on the PCB. By default, “R19” is not populated, which selects Mode 1. To enable Mode 2, a 47kΩ 0805 resistor must be soldered onto the “R19” pads, and to enable Mode 3, a 120kΩ 0805 resistor must be fitted in the same position.
MODE 1 (R19 = Open) – Pulse Width Output:
- This is the default operating mode and does not use UART communication. It operates using a standard trigger/echo timing method.
- The “TRIG” pin must be driven HIGH for a minimum of 10µs to initiate a measurement cycle.
- Upon receiving a valid trigger pulse, the module emits eight 40kHz ultrasonic bursts and then listens for a reflected echo.
- The “ECHO” pin goes HIGH during the echo detection window. The duration of this HIGH pulse represents the round-trip travel time of the ultrasonic wave.
- Distance can be calculated using: Distance (cm) = Pulse Width (µs) ÷ 58 or Distance (Meters) = (Pulse Period * 340m/s) / 2
- If no valid echo is detected, the “ECHO” pin will automatically return LOW after approximately 40–60ms, indicating the end of the measurement cycle.
- A minimum measurement interval of 60ms is recommended to prevent signal overlap between measurements.
- The onboard LED lights up when a measurement is triggered. It is not a power indicator.
MODE 2 (R19 = 47kΩ) – UART Automatic Output:
- In this mode, the module automatically performs a distance measurement approximately every 100ms without requiring an external trigger.
- The measured distance is transmitted via the “TX” pin using TTL-level UART communication.
- Communication format: 9600 bps, 8 data bits, no parity, 1 stop bit (8N1).
- Each data frame consists of four bytes: 0xFF (header), High Byte of distance, Low Byte of distance, and Checksum.
- The distance value is transmitted in millimetres as a 16-bit integer (H_DATA + L_DATA).
- The checksum is calculated as: (0xFF + H_DATA + L_DATA) & 0xFF.
- If the measured target is out of range, no valid data frame is transmitted.
- This mode is ideal for applications requiring continuous real-time distance monitoring.
MODE 3 (R19 = 120kΩ) – UART Triggered Output:
- In this mode, the module remains in standby after power-up until a measurement command is received.
- A single measurement is initiated by sending command 0x55 to the “RX” pin.
- After receiving the command, the module performs one measurement and transmits the result via the “TX” pin.
- Communication format: 9600 bps, 8 data bits, no parity, 1 stop bit (8N1), TTL level.
- The output data frame format is: 0xFF + High Byte + Low Byte + Checksum.
- The checksum calculation is identical to Mode 2: (0xFF + H_DATA + L_DATA) & 0xFF.
- A minimum interval of 60ms between trigger commands is recommended.
- This mode is suitable for controlled polling systems or applications with multiple sensors sharing a UART interface.