Im now looking into my college engineering project and am looking into making a car parking sensor.
Ive got all the basics, the only query i have is whether 2 or more HC-SR04 modules can be connected somehow so to increase the reliability in the distance measurements. 1 module i don't think will be sufficient.
Increasing the number of sensors for car parking:
1- Can increase the coverage that you wanna detect obstacles in.
2- Can detect which side of the car has obstacles in according the reading of each sensor.
To minimize the error of the distance, you can get the average of multiple samples (i.e. taking the average of a burst of 5 signal readings called Debounce).
Hope you find it useful,
college engineering project
College or Lycée
STI2D or S-SI