I am trying to detect a table tennis ball passing trough a polypropylene pipe. (Don’t ask why just yet. It’s a secret.) The ball is propelled trough the pipe by air pressure from a centrifugal fan. I have been using a Sharp Infrared Proximity Sensor for this but it has several drawbacks:
- The hole needed in the pipe is quite big, approximately 10 by 40mm. This leads to a loss of air pressure and the ball moves slower.
- The sensing range of the sensor is 30 to 400mm so the bracket for holding the sensor needs to be quite big since the sensor needs to be mounted at least 30mm from the pipe.
- The ball moves so fast trough the pipe that the sensor is not fast or accurate enough to detect the ball passing. The ball is detected but the sensor reading is not high enough to rule out any errors .
Today i started testing these tiny sensors from SparkFun. An emitter, marked with a yellow dot and a detector marked with a red dot. The emitter is connected with a 270 Ohm resistor and the detector is connected with a 10k Ohm resistor. The tests I did with a breadboard and an Arduino Uno was very promising.
I made little packages with the sensors and resistors connected to Molex connectors for connecting to a Phidgets interface board and mounted them on the polypropylene pipe. This method seems foolproof. The ball is detected every time even at very high speeds. Now I only need to figure out how much interference I will get from ambient light and from using several of these at the same time. Finding a way to mount them without tape is also going to be interesting.