I have a weak signal (from a photo-diode) which I need to amplify to drive an LED. I try to accomplish this with an OpAmp TL081 and the circuit given in the image.
What the circuit does: When there is no signal (even if the photo-diode is not even connected), there is a voltage at the LED (about 2.63 V). When the photo-diode is replaced by 0 Ohm resistor, the voltage at the LED increases marginally.
What the circuit should do: When there is no signal, there should be no (or little) voltage at the LED, when there is a signal from the photo-diode, there should be about 3.36 V at the LED.
As possible error sources I identified:
- mistake in the circuit design
- mistake when soldering everything together
- corrupt element (e.g. burned IC)
Question: Is the circuit design ok? Addon: If yes: did I miss any other possible error sources?
I think the used schematic is like this (if I got the wiring to the OP Amp right, which is not given in this schematic):
Edit: Orientation of photo-diode was wrong in the diagram, as pointed out by the answer of Andy aka (Thanks!). (At least it was right in the build circuit and therefore not the reason of the problems, but of course this needed to be fixed.)