All, I ordered some of the TCRT5000L photo reflective switch units from Amazon, and when they arrived it is not clear which way round the IR LED / Sensor polarity is. I am used to either a flat on the side of the LED or one leg of the attaching wires to be longer than the other, but in this case these features are not present. To make it worse, some of the sensors had dropped out of the plastic housings and when I try and use the remaining ones for reference, they are completely randomly placed.
How can I tell how to wire them up?
Maybe I didn't explain properly - I am saying that the physical parts have no distinguishing features to identify the cathode or anode as far as I can tell. If you look at the data sheet, it is easy, assuming the parts have not moved position or dropped out entirely. As far as I can ascertain, the usual polarity markings are absent, so maybe there are some that I am unaware of or is it that there is no polarity requirements (unlikely looking at the data sheets online)
If I can't work out which leg of the device is the anode it's going to be tricky to wire it up correctly. if they were supplied with the two devices firmly installed I could use the housing as a reference, however I can't as they are loose and a load dropped out. I have no way of knowing if they are correctly oriented if still installed
OK, I see the problem now.
Using your multimeter on “diode test” should allow you to identify anode and cathode of the LED (the blue one) as being IR, it should register as about 1.2 V. Alternatively, view the LED with your digital camera while you do the “diode test”.
If you could see through the encapsulation of the phototransistor, you could see on which side the die is mounted and compare the loose ones to the mounted ones.
Otherwise you are going to have to set up a breadboard and use an Arduino program to connect the sensor between a pin and ground using INPUT_PULLUP to read the phototransistor while you sit it in the sun. Then mark the emitter side with a black marking pen.
Thanks, I certainly have nothing to lose by trying that!. I do have a digital camera, and now I think about it I do remember seeing the IR emitter on the remote flashing when it was commanding.
Thanks for the help