Needs references for photocells ?

[demether]

Hi

I just realized that I don't have a clue on what I need to buy for my tracs sensors :think: I don't know what are the best references to buy.

The only thing I know is that I'd like a detection inside the track, if possible without external light, but if it's absolutly needed, at least not visible light.

I'm currently doing my shopping list, since the track parts should be delivered after tommorow.


thanks !

[RichD]

There are two types that can be used, photo resistors and phototransistors. Photo resistors require a lot of light, so most people use phototransistors that are sensitive to invisible infrared light. Special infrared emitters are usually used with the photodetectors. The emitter/detectors can be arranged so that they are on either side of the slot for each lane as in the Carlson Sensor Track. Emitter/detector pairs can be purchased that are built into a single housing. With that arrangment the car's guide flag is what triggers a count, some guide flags do not work well with sensors that look across the slot. The most common arrangement is to have sensors that are flush with the track surface and emitters that are located in a bridge over the track. It is best to power the emitters with their own supply. The sensors only detect light at a certain frequency, so they must be used with matching emitters or you could miss counts. Radio Shack sells an emitter and a detector in a package, but they are not well matched and will only work well if they are close together.

[demether]

Thanks !

I'll order phototransistors with matching (and same brand, built for them) IR leds. ;)

I hope it will work correctly !

[dr fabio]

How strong is your basic electronics? Ive built many timing circuits for various guys in our club with false trigger circuitry. Most basic designs tend to false trigger a lot when lots of cars are running with all the electrical noise they make. The circuit is not just your basic IR LED and phototransistor. I could send you a diagram but its not a basic build.

I use an IR LED and IR phototransistor. Common ones have the wavelength centered around 850 or 940nm. Just make sure they are matched. Just type in some key words like IR LED, or IR diodes, IR receiver, IR phototransistor etc into ebay.

Try ebay: IR phototransistor
http://www.ebay.com.au/itm/200pcs-5mm-9 ... 2267wt_916

IR LED
http://www.ebay.com.au/itm/5-PCS-3mm-94 ... 1598wt_916

[demether]

That's it, 940nm. I found a french store where they sell the IR phototransistor and the matching IR led (same brand, the IR led is specifically designed and tested for this phototransistor).

I will also use a separate powersupply for the IR leds. The phototransistors will be plugged on an Arduino MEGA board, using Race Coordinator software.


We'll see how it works !