I have made this circuit (below) for laser detection in my work with photodiode in (X1-1 ; X1-2) and Arduino. Everything works perfectly.
For technical reasons, I wish away the photodiode from the board (arround 1.5 m). But when I put a cable (02x0.4mm) greater than 30 cm between the photodiode and the board , transistors engage, as if there were laser detection.
I try to put variable resistors between the first transistor, but it has nothing do ...
any help would be welcome, as I am completely stuck