How can I detect a break in a light beam?

[Guru]

I want to detect when a Scalextric car passes a certain point on the track

I've seen this dome with a light source above the track and something set into the track to detect when the car passes

I understand this is done using a light sensitive transistor set into the track and connected to the joystick port.

My questions:

Is a light sensitive transistor called something else because I can't track any down?

How does it connect to the joystick port?



Thanks

[Devion]

I don't think it's a small little box you just buy in a general store.

The joystick port is also a midi port and can thus receive data from any device that can send data (and apps listening to the midi/game port can act on it).

How it's connected to the midi port or lpt/com. I dunno. If you want to try such a project you might first want to go and buy the parts required (and a soldering iron) as you would probably have to put it all together yourself.

Pin layout and such is important and it's either documented by the company making the PCB/Sensor units or you'll have to figure it out yourself and develop your own communication application to communicate via those pin layouts (RX/TX/etc)

[penagate]

I've got one of those light sensor things somewhere, but I've forgotten what it's called too

AFAIK, light shining on it produces a current. Hence, it would need to connect to some sort of device, which then could connect to any port you wanted.

Do you have one, or looking for one?

[Guru]

OK, so I now know that it's called a phototransistor

I have also tracked down a description of the joystick port

[CVMichael]

AFAIK, light shining on it produces a current.

Actually a phototransistor changes resistance... and you have to use it with a transistor, kinda like this: