Description
AJ-SR04M_ver2 is an economy version Waterproof Ultrasonic sensor widely used to sense water level in overhead tanks.
In normal mode which is Trigger mode it works as classic SR 04 Ultrasonic sensor by sending a 40khz burst and receiving at ECHO pin to measure distance.
R19 Resistor pads are open for this mode.
If you solder 120k resistor at R19 it works in UART mode.Here it waits for 0X55 value and then receive a packet of 8 bytes to calculate distance of object.