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
MarkT:
You need shielded coax cable to the diode, you are just picking up RFI.
[ well probably. Another possibility is oscillation. ]
Indeed, it is quite logical explanation for coax ... I will try tomorow . What do you mean with oscillation?
You might have turned the circuit into an oscillator since it uses a feedback network
and the input cable adds capacitance changing the phase response of the feedback.
I just test a Coax cable , no more problems .. Thank you!
You think a Cat.5 FTP network cable can also do the trick? Because I would put several photodiode in parallel.