Science Buddies: "Ask an Expert"

Hi,

I've built Zippy the line following robot, but the IR sensor on one side is not working. The wheel spins as soon as the power is turned on. It does not turn off at all until the power is turned off - even in a completely dark room, or if the IR sensor is completely covered. We've checked all wiring and everything is exactly as shown in the diagram. What do you suggest?

Try switching the two IR sensors and check if the problem persists. If so, one of the IR sensors is faulty and should be replaced. If not, please check the wiring again. Unless the circuit board or wires themselves are damaged, the wheel shouldn't be turning if the IR sensors is not detecting anything.

-Karen

Thank you, we ended up replacing two of the IR wires (blue and black) and noted that the diagram of the breadboard is different than the photograph of the completed car. The diagram shows an additional resistor that the car photo did not. These two things seemed to solve it. However, the car still doesn't go on the line for more than 2 feet. After much sensor moving around, the best we've done is have it wobble down the line then veer off to one side. Adding weights to the car helped stabilize it, and we reduced speed by changing to the 3-battery pack, but we also put in the smaller resistors. I think we need to go back to the larger resistors to slow it down further. Thank you!