I'm experimenting with a "Beam-Breaker" setup to sense presence of rolling stock on a model railway layout. I'm using a TSUS5400 IR emitter and have paired it with the following sensors, which appear to work equally well
1) A BPW41 IR diode (2 legs), used the "Right" way around i.e. anode to the + side of the circuit, cathode to the A0 pin (with the resistor to ground, circuit schematic attached).
2) A L-7113P3C Phototransistor
Each seems to work perfectly well - so I have a couple of questions.
What I mean by "Works" is that (after juggling with the resistor value) I get a max reading of 1023, LED On, for distances up to about 5cm, tailing off up to 10cm, and with drops in readings of varying amounts depending on the sort of rolling stock I pass through the gap, whether the item is closer to the emitter or the sensor etc. - in short, beam not broken get high reading, beam broken get low reading. Plus various ambient effects depending on lighting, sunshine etc. But the circuit I'm using looks too simple!
My questions are
1) I've read in several places (but can no longer find the links!) that the IR Photodiode should be connected the "Wrong" way around i.e. with the Cathode to the + side of the circuit (Schematic attached), but I don't see the benefit of this - or even that it would work. Could someone explain please in simple terms? NB I haven't tried it yet in case I've misunderstood, and end up blowing something up!
2) I'm not sure of the differences/benefits of the IR Photodiode v IR Phototransistor - again is there a simple explanation (in my context)
Many thanks for your help, just want to understand what I'm doing and why, rather than settling for an "It works" approach, but my electronics knowledge is almost zilch so I don't understand most of the explanations I've "googled"! - Dick.
PS Once I've finished I'll be happy to post up my results
UPDATE Please see my somewhat embarrassed "Reply" of 25/02/2014 @ 19:25