The JSN-SR04T clone ultrasonic module is comprised of a waterproof ultrasonic transceiver (Transmitter and receiver) and a separate control board. This control board not only drives the ultrasonic transceiver, but also provides an interface for a microcontroller to connect to which can be used to trigger and read results from the transceiver. Ultrasonic sensors are able to measure distance by using high frequency, inaudible ultrasonic waves. When triggered, the module sends out a few of these waves and receives the same waves reflected back from the target (If there is one within range). The distance between the module and the target can then be calculated from the transmission and reception time of the waves.
Features / Specs
- Model: AJ-SR04M (JSN-SR04T Compatible)
- Operating Voltage: 3.0 – 5VDC
- Operating Current: < 8mA
- Ultrasonic Transceiver Frequency: 40kHz
- Sensing Angle (Max): 75°
- Detection Range: ~(20 – 600cm)
- Resolution: 1mm
- Distance Accuracy: ±1cm
- Output Type: Digital (High level is VCC)
- Operating Temperature: -20℃ to +70℃
- Cable Length: 2.2 Metres
- PCB Dimensions: ~(42mm x 29mm x 12mm)
Basic Operation Overview
The JSN-SR04T clone ultrasonic sensor has 3 different modes of operation. The value of the SMD resistor “R19” is what sets the current mode of operation. By default this resistor is not soldered on the PCB, thereby selecting MODE 1. To select MODE 2, you will need to solder a 47k-Ohm 0805 resistor onto the pads of “R19”. MODE 3 requires a 120k-Ohm 0805 resistor. That being said, let’s discuss each mode in more detail.
MODE 1 (R19 = Open):
- This mode does not use any communication protocols and requires a trigger pulse to start an ultrasonic probe.
- The “Trig” pin must be driven HIGH for a minimum of 10μs.
- On receiving a valid trigger pulse, the module sends out eight 40kHz square wave pulses through the ultrasonic transceiver and waits for an echo.
- The module will drive the “Echo” pin high regardless of whether a valid target is within measurement range.
- If a valid target is within measurement range, the period of this output pulse will be equal to the time between the transmission of the ultrasonic pulse, and the reception of the corresponding echo.
- Using this measured period and the speed of sound (~343 meters/second 20°C in dry air) we can calculate the distance between the sensor and target being measured. The formula is: Distance (Meters) = (Pulse Period * 343m/s) / 2
- Remember that with each measurement the sound waves must first travel to the target, reflect off of it, and then travel the same distance back to the sensor. This is why we divide the calculated distance by two in the above formula.
- Lastly, if there is no valid target within measurement range, the sensor will drive the “Echo” pin low again after 60ms.
MODE 2 (R19 = 47k-Ohm):
Operation description coming soon …
MODE 3 (R19 = 120k-Ohm):
Operation description coming soon …