Is this project feasible?????

[larsof54]

Is this project feasible?

I want to build a cue ball speed detector for when I break a rack of pool balls. I want to place a box on either side on the pool table sitting on top of the rails. The boxes are 6 inches long. One box will have a couple of IR emitters and the other box will have a couple of IR receivers as well as a 3-digit 7-segment display. The boxes will be 50 inches apart.

The distance between the beams (50 inches) along with estimated top speed (40 MPH) and allowable error (.02 MPH) dictate that I must detect a beam broken condition in 4 microseconds or less.

That lets out the TSOP7000 type of receiver and leaves photodiodes or phototransistors.

I have breadboarded some phototransistors. They work ok if they are close together but not so well as the distance increases.

Is this project feasible or am I dreaming?

LW

 

[keith1200rs]

What you want to achieve is certainly achievable.

Photodiodes, particularly PIN ones, are considerably faster than phototransistors (1 or 2ns for a fairly cheap 1mm one). One way of doing it would be to use a couple of cheap laser pointers so you can get plenty of light onto the photodiodes.

Keith.

 

[flatulent]

One problem to face is the interference from the room lights. An easy solution is to drive the emtters with a square wave of a few 10s of KHz. Then on the receptor end use an amplifier chain with a band pass filter of the same frequency.

 

[keith1200rs]

One problem to face is the interference from the room lights. An easy solution is to drive the emtters with a square wave of a few 10s of KHz. Then on the receptor end use an amplifier chain with a band pass filter of the same frequency.

True. Although if you use a laser source there will be so much light you may get away without needing to modulate.

If you do modulate and want to resolve a few us then you will need to modulate at a few MHz.

Keith.

 

[larsof54]

I figured that 125kHz would do the trick. I could be out by 1/2 a cycle on either beam which gives me the .02 MPH error factor I'm after.