optical detection

[inservi]

Hello,
I'm sorry, I know this is not the best forum for my question, but I do not know others in the electronic in general.
If you know a good forum please tell me now?

I want to detect the passage of slot racing car 1 / 32. After testing different kind of sensor (hall effect ...) I think the best system is optical. The good idea is to make a bridge with LED emitting a signal and a photo transistor for receiving and detecting a change in the way. I can not make a hole or any change in either the runway or in the car. Thus, the emitter and receiver must be in a bridge at about 17 cm (6.5 inches) above the runway. Is there someone who already had a system like this? I guess I need a focusing lens to the receiver to find where the car is passing. I should see a radius of about 3cm ( 1 inch ) to about 17cm (6.5 inches).

An other possibilities would be by detector hall but it must be sensitive to about 5 to 10 Gauss and deliver an analog signal.

Thank you in advance.

Daniel
_________________
in médio virtus

[John P]

Why can't you have a light beam shining across the track, and sense the car breaking the beam?

If you have to use a reflective system, then the reflectance of the track must be different from the reflectance of the car, or perhaps you could make use of the angled surfaces on the car versus the flat track. You need to set up your components and look at the output of the sensor on a meter or a scope while you move the car around by hand. If you see a significant change in output then you have a good chance that this could be a workable system.

[Wayne_]

I can see that you would need to monitor each lane to know which car passed but if it is the new digital system each car can run in each lane can't they ? I am no slot car expert

Sensors on a bridge should do it and as the track is black it may just pick the cars up with ambient lighting and a simple sensor, you may need to attach a reflective strip to the top of each car.
A small tube over the sensor directed at the track may be all you need to pick up a single lane.

I would just try it and see.

Another option would be to place a coil under the track in each lane. The cars have electric motors with magnets in so this should generate a small current when passing over the coil, this would need to be tested.

If you do need to distinguish between cars then it gets a little harder. You could use RFID tags on the top of each car or a barcode type system.

Wuold be interested to know how you did it in the end. Not that I do slot car racing.

[inservi]

Thank you John,
The beam passing through the runway would be very effective and easy to do, but I can not make any hole in the runway because I wish I could move the system in case of need on the tracks of other clubs.

I have not yet found a system without optical lens that gives me a good signal without much sensitivity to ambient light noise.

Best regards,
Daniel
_________________
in médio virtus

[inservi]

Thank you Wayne
I do indeed follow each track because we do not use car digital system.
It seems a diagonal beam should give good results but with a focusing lens I think.

I'm currently testing with coils and it works very well for one track. But when I put the 4 detectors, they disturb each other because they are only 10 cm from each other, and I have to adjust the sensitivity to detect the engine at about 3cm (1 inch). There are some weird effects

The RFID tags would be a good solution, but it must then place a tag on each car, the owners do not like this kind of change in their models. It is also faster because the antennas standard 125KHz is not fast enough to detect crossings lasting approximately 10-50 ms for some cars. The speediest RFID system is most expensive.

If the optical system is too complicated to achieve, it remains as the Hall effect sensors, but i find a sensitive enough.

Best regards,
Daniel
_________________
in médio virtus