Can someone help me with using the HC-SR04 as a switch please?

[Lance Maddux]

(I'm using Ardublock) My only purpose of using the arduino is to sequence my traffic light collection which I've got the timing of the lights and the sequences down packed but I am trying something new. I tried using a PIR motion sensor to do an if/then-else sequence where if motion is detected, my signal will do a green light cycle with an accompanying yellow and red cycle and if no motion is triggered, a flashing yellow arrow for a certain amount of time then a solid yellow and red cycle, but I could never get the PIR motions sensor to work right (cheap chinese ones). So I invested in a HC-SR04 proximity sensor and I am having the same headache. All I would like to learn is how to use the HC-SR04 as a switch so that when there is motion, my signal will turn green and if no motion, will flash yellow. Thanks!