That'll work if the base lead is available on the phototransistor. I don't think it is on the RadioShack one. It's just a 2-lead T1 3/4 case similar to an LED.
In any case, it should work "as-is". A lower voltage drop gives a larger margin of error. You can use a higher value resistor to "dim" the LED as well. It'll be plenty fast enough, adding a B-E resistor will make it faster, but that only matters if you're dealing with microseconds time frames. The ball will probably take 1/10 second to pass at least.
Have you tested it in the ball tube yet? Make sure to test it in the dark (no ambient light hitting the tube or phototransistor) to ensure the LED is "shining" enough IR on the transistor to keep it "on" with no ambient light entering the tube.
Since you have the photodiode already, it would be interesting to test it with a transistor to see if it performs similarly.
I was going to mention if ambient light will cause a problem, but since you're sensing the blockage of light, the ball would block out the sun as well when it drops into the tube, so that shouldn't be a problem either.
In any case, it should work "as-is". A lower voltage drop gives a larger margin of error. You can use a higher value resistor to "dim" the LED as well. It'll be plenty fast enough, adding a B-E resistor will make it faster, but that only matters if you're dealing with microseconds time frames. The ball will probably take 1/10 second to pass at least.
Have you tested it in the ball tube yet? Make sure to test it in the dark (no ambient light hitting the tube or phototransistor) to ensure the LED is "shining" enough IR on the transistor to keep it "on" with no ambient light entering the tube.
Since you have the photodiode already, it would be interesting to test it with a transistor to see if it performs similarly.
I was going to mention if ambient light will cause a problem, but since you're sensing the blockage of light, the ball would block out the sun as well when it drops into the tube, so that shouldn't be a problem either.
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