Recently I was working on the IR obstacle sensor. It doesn't work properly if both receiver and transmitters are connected to the same power suply! It started to work properly when I suplied the generator from the another power source. But if the transmitter diodes are to close to the receiver it still doesn't work. The receiver is active all the time, even if it's covered. I suppose that there are some electromagnetic interferences. I must simply move the diodes away.