AJ-SR04M Waterproof Ultrasonic Distance Sensor Module – Integrated Ultrasonic Ranging / Parking Radar System

Description

The AJ-SR04M is a robust, industrial-grade waterproof ultrasonic distance sensor module designed for harsh environments where standard sensors would fail. Unlike conventional ultrasonic sensors with exposed transducers, the AJ-SR04M features a completely sealed, waterproof probe connected via a generous 2.5-meter cable to a dedicated control board . This allows the sensing head to be mounted in damp, humid, or dusty areas (such as rainwater tanks, outdoor robotic platforms, or automated parking systems) while keeping the control circuit safely housed in a dry location .

Utilizing non-contact ultrasonic detection technology operating at 40kHz, it provides stable and accurate readings. It reliably detects planar objects from as close as 20cm up to 800cm (8 meters) under optimal conditions, with a precision resolution down to 1mm to 3mm . The module’s wide operating voltage of 3V to 5.5V DC makes it compatible with both 3.3V (ESP32, Raspberry Pi) and 5V (Arduino) microcontrollers, eliminating the need for level shifters in most cases .

One of the AJ-SR04M’s most distinctive features is its versatile operation with 5 different modes, configurable via the ‘R19’ resistor pads on the control board :

• Mode 1 (R19 Open): Default factory mode. Operates identically to the classic HC-SR04 using standard Trigger (10µs pulse) and Echo pulses.

• Mode 2 (R19 = 300kΩ): Low Power Mode. Ideal for battery-operated devices needing minimal current draw.

• Mode 3 (R19 = 120kΩ): Automatic Serial Port Mode. Board continuously outputs measured distance over the TX pin at 9600 baud.

• Mode 4 (R19 = 47kΩ): Low Power Serial Port Mode. Module sleeps until it receives a trigger byte, measures, reports distance, and returns to sleep.

• Mode 5 (R19 = 0Ω / Bridged): Computer Printing Mode / Continuous Serial output mode.

The ultra-low standby current of under 2mA (and as low as 20µA in certain low-power modes) makes it an excellent choice for battery-powered and energy-conscious applications . The single fully enclosed transducer handles both sending and receiving, simplifying installation and protecting the sensor from water and dust ingress .

The AJ-SR04M is widely used in rainwater harvesting systems, water tank level monitoring, outdoor robotic obstacle avoidance, automated irrigation, smart parking management, and industrial control applications . Its robust design and reliable performance make it a superior alternative to the standard HC-SR04 for any project that requires durability and weather resistance.

Features

• Industrial-grade waterproof probe — Sealed transducer and cable designed for wet, humid, and harsh environments

• 2.5-meter cable length — Allows the sensing head to be mounted remotely from the control board

• Wide 8-meter detection range — Measures from 20cm up to 800cm (8m) under optimal conditions

• High accuracy and resolution — 1mm to 3mm precision for reliable distance measurement

• Wide operating voltage — 3V to 5.5V DC, compatible with 3.3V and 5V microcontrollers

• Five selectable operating modes — Configurable via the R19 resistor pads for GPIO, UART, and low-power applications

• Ultra-low standby current — Under 2mA standby, with low-power modes down to 20µA

• Integrated waterproof transducer — Single enclosed probe handles both transmission and reception

• No level shifting required — Works directly with both 3.3V and 5V logic systems

• LED status indication — Onboard LED indicates module status and measurement activity

Technical Specifications