The HC-SR04 ultrasonic distance meter
The
HC-SR04 
emits an ultrasonic sound wave and measures the time it takes to travel to a target and back. Knowing that sound waves travel at 330m/s the distance between the sensor and the target can be calculated
The cabling is done as described in the following table
* Because the signal emitted by the HC-SR04 has a 5V level and the ESP32 CPU accepts only 3.3V signals, the ECHO signal is passed through a 1kOhms / 2kOhms voltage divider.
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Uli Raich - 2022-05-30
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