This is another biased usage. After all, MAX232 is not used for this, but it is also a very clever solution to use a 5V power supply to drive an ultrasonic probe.
MAX232 is a TTL-RS232 level conversion IC. It has a charge pump inside, which can change the 5V power supply voltage into ±10v~±15v, and output signals at this voltage. This circuit is a typical RS232 working circuit, but the output is connected to an ultrasonic sensor to convert the TTL signal (0-5V) output by the MCU into a ±15v output.
Ultrasonic sensors are generally piezoelectric ceramic materials, capacitive devices, with high driving voltage and small current. The effect of direct driving with 5V is very poor. The designer of this circuit used MAX232 to boost the voltage. This is a very clever and unorthodox method. You can learn it (I also learned it), but regular products require Use with caution hehe.