I'm building a Soccer Robot for the RobocupJunior Competition. The game consists of two robots in each team, and one ball that emits infrared at 40Khz of frequency. For Long distances, whe will use the "digital" infrared sensors, but for closer distances, we need to know at least "proportionaly" to the distance to the ball. That's why we want to put some analog infrared sensors around the robot also. But, analog sensors are really noisy, and we need a "filtering" circuit for 40Khz.
I have read a lot about filtering circuits, but when i get into the practice, i don't know what to do...
So, does any one of you, know how to filter one specific frequency with an analog sensor?