Whiskers on robots are simple sensors that work like an animal's whiskers, picking up on things in the environment that are close by. When the sensor is moved, it sends a pulse to the robot to let it know there is an obstacle.

Steel guitar strings can be used to make whiskers that are sensitive and inexpensive for general use. These strings are very flexible, easy to use, and conduct electricity. Take a copper tube that is 2 cm long and 4 mm wide. Cut a 10-centimeter piece of guitar string and slide it into the copper tube. Use a rubber bush insert at the tube's end to keep the string in the middle of the tube. Figure 1 shows how the last mechanical whisker should look. Solder a wire to one end of the copper tube and another wire to the end of the steel string. Only one of the four channels that can be made with one LM339 is shown in the diagram (IC1). The IC LM339 series is made up of four independent precision voltage comparators. The offset voltage for all four comparators can be as low as 2 mV. These are made so that they can work on a wide range of voltages from a single power source. Here, we have only used the first one. Pin 5 of the IC LM339 is a non-inverting input, and resistors R2 and R3 connect it to a fixed voltage. As shown in Fig. 2, the inverting input (pin 4) is pulled high by R1 and connected to the mechanical whisker. Because the LM339 only has open-collector outputs, the pull-up resistor R4 is used. The way it works is easy. At first, when there are no interruptions, the comparator's output stays low. When something touches the guitar string of the whisker switch, pin 4 of IC1 goes low and pin 2 of IC1's first comparator goes high for a short time. We've only talked about one comparator, but the other three can be used in the same way. Through this comparator output, the robot's brain, or microcontroller, can now find out what the whisker switch is doing.