Etgernet + wifi

[kulibin]

if the HC-SR04 output dry contact signal, you can connect with free gpio ports or digital input ports.

HC-SR04 has two controlled outputs Echo Output Signal and Trigger Input Signal.  Which terminals should I connect sensors to?
The TRIG pin is responsible for sending the ultrasonicburst. This pin should be set to HIGH for 10 μs, at which point the HC­SR04 will sendout an eight cycle sonic burst at 40 kHZ. After a sonic burst has been sent the ECHO pinwill go HIGH. The ECHO pin is the data pin ­­ it is used in taking distancemeasurements. After an ultrasonic burst is sent the pin will go HIGH, it will stay highuntil an ultrasonic burst is detected back, at which point it will go LOW