I have played around with IR beams, and I wonder how to receive the signal. I just want to know whether my beam is broken. The system will at the end work in a dark space. If blocked it will block almost completely.
I tried with a phototransistor and a photodiode. I am using 890nm. There is app 50 cm / 2 feet between transmitter (always on) and receiver.
My question is on the receiver. I have tried to feed base or gate of a transistor, with my phototransistor on the plus side, 10K to the base/gate and 1M to ground. The system works only within 5 cm or so. At 40 cm of distance, there is only 0.07V on the resistor side (the 10K). In my room, with very little light I get only a 0.02 difference whether my IR LED is on or off. On google I find example of a photo transistor feeding a normal LED directly. Trying that at 12V still does not turn on my LED. I have tried some phototransistors and one taken from a sensor/optokobler (I cut it in half and used them with a bigger distance) Try my TV remote etc I get the same result, only a very week change.
The receiver is supposed to work on 3V or to batteries when ready.
Regardless of what I do I only get a weak change of 20-30mV. I can move LED and phototransistor and clearly see a difference in angles by a few mV.
Given that I work in a dark space, I could simple use a comparator or opamp to boost the signal, simply look at say signal > 0.04mV.
How are other peoples experiences with IR receiving? I work at a low voltage, so recivers for Ardoino is not really an option. I and want the joy of working with this development
PS: I recall a friend many years ago using a 555 to send 2 frequencies for 0/1 and receiving it in the other end. Has anyone done anything similar?