Determening the location of a ball contacting a surface

I'm a student currently working on a project. I have two objects, one of which is a plastic ball. The other is a rectangle which is being hit with said ball. My goal is to detect a position of a hit. The rectangle is about 5x5 cm. What would be the least intrusive way of sensing a position of a hit?

Perhaps I could use some kind of sensors on the rectangle to try and triangulate the position? Maybe put a small magnet on a ball (d=3cm) and with a help of small coils on the rectangle to calculate the position (could that work? or is it just stupid?) Small current would induce on each coil. How about putting a thin metalic film on the ball and an array of small (+) pads and an array of detection pads (grounded via pulldown resistor)? Like a matrix.

• What about a camera? – Claudio Avi Chami Mar 6 '17 at 12:38
• Camera idea is good. Also, you can explore IR sensors too. QRE1113GR ex. – Umar Mar 6 '17 at 15:20

Not stupid idea, but use soft low remanence iron ball instead of a magnet. It's position is arbitary, nothing needs to point to some specific direction. Have an external DC magnetizing coil and some small pickup coils. Measure the pulses induced to the pickup coils.

The hard part: You must match some complex function that gives the hitpoint coordinates from the pulse amplitude proportions. It can be a table of premeasured values and the intermediate values can be got by interpolation. Triangulation may be useful or not.

DC magnetizing might be better to replace with high enough frequency AC to get stronger signals. That would eliminate all effect of remanence and earth magnetic field. Also the eddy currents can increase the detectability. You must explore with hf magetization, which phenomena gives the strongest effect.

Iron powder+glue or ferrite ball has no eddy currents, a copper ball has nothing, but eddy currents, solid iron ball has magnetic effect that is affected by eddy currents.

Totally different approach: Learn how resistive or capacitive touch panels work

The next: have some microphones or schock sensors. Triangulate from timing differences. Actually, to get the result fast, compare with a table of prestored timing patterns and iterate or interpolate.

And still one more: One schock sensor gives the hitting time and triggers 2 perpedicular line cameras or lightport arrays. The software finds the mass centres of the shade patterns and these are your coordinates

Good luck!