I want to build a systems that measures if some parking spots are occupied or not. I chose to use an ESP8266 12-E NodeMCU Kit with multiple HC-SR04 ultrasonic sensors. In my project, it is essential to connect as many ultrasonic sensors to one ESP. Unfortunately, I have found out that if I connect the input/output of the HCSR04 to GPIO 10/9 and GPIO 1/3, The board can't boot. Can anyone explain to me why I cannot use those GPIO pins and what alternatives I have in order to connect more sensors to the ESP (other microcontrollers, pin extenders etc.)?

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