technical interviews for high-tech professionals





 =Brainstorming technical problems= 



  • Vball13.
    OK, first thought - put sensor into a tennis ball, something like RFID...
    No, bad idea: these balls will differ from standard ones. Besides, implanting sensor into tennis ball is not as easy as it may sound.
    I suggest to use a video camera to measure the speed of a tennis ball during service. NTSC video has a rate of 30 shots/second. A maximum speed of a tennis ball is 150 miles/hour, which is 220 feet/second. That meens that the ball may cover up to 7 feet between the adjacent video shots. The camera can be placed on a side of the court to shoot along the net. The view area of the camera should be wider than 7 feet to ensure the ball during service will be captured on the two adjacent shots. The software can do the processing by comparing the locations of the ball on the adjaicent shots to calculate the speed. On the drawing the view area of the camera is shown in red, blue line is the trace of a ball.

  • shuking.
    I back up the idea of video capturing to measure the speed. I think, however, that shooting along the net suggested by vball13 will introduce some error. I added to the drawing lines a, b and c to illustrate possible traces of a ball at different angle. The difference will not be recognized on a video capture if a camera is placed at the hight of a net. Putting camera 10-20 feet above the net should fix the problem.