I just completed a set of whisker-type sensors for my soon-to-be mobile robot. I had seen several such designs elsewhere on the Web, but each had elements I didn’t like, such as that the antennas were electrified. I eventually arrived at the hybrid design shown below.
In this design, one end of a spring is soldered to a PCB, but the other end is left free to move. A U-shaped loop of wire surrounding, but not touching, the free end of the spring is soldered to the PCB. Then, an insulated probe is inserted into the free end of the spring. When the probe collides with an obstacle, the spring moves and makes contact with the loop, completing the circuit.
Here’s the finished product.