For a university project, I have to use this photodiode.

I've tried following two circuits for a photodiode that I found here on the site. How to Use SFH235 IR Photodiode Correctly?

However, the circuit on the right with the op-amplifier, we can only get it to output 0. And with the circuit on the left, i also find the output strange. With a regular lit room, it outputs 67-70, but it is exactly the same without any light, and with a bright light-source shining onto it, it outputs around 95. Does anyone have any suggestions as to what could be wrong?

my circuit, gray being 5V, green ADC, orange GND


closed as unclear what you're asking by Olin Lathrop, Leon Heller, Daniel Grillo, Dave Tweed Nov 18 '16 at 15:47

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    \$\begingroup\$ Photodiode overkill? Looks expensive. \$\endgroup\$ – Bradman175 Nov 18 '16 at 13:59
  • \$\begingroup\$ Do you have to specifically use that part? If you are unfamiliar with electronics I'd recommend starting with a LDR. \$\endgroup\$ – Wesley Lee Nov 18 '16 at 14:09
  • \$\begingroup\$ You show a single picture, no schematic, so there is no "circuit on the right" or "circuit on the left". This really should be obvious. Closing this mess. \$\endgroup\$ – Olin Lathrop Nov 18 '16 at 14:17
  • \$\begingroup\$ I'm also concerned about the website. They seem to have suggested the wrong datasheet along with the product. It should be this one. farnell.com/datasheets/… the photodiode responds to green the best. I have no idea why who ever assigned you this asked you to use a photodiode that is meant to kinda replicate the m cone spectral sensitivity of the eye. Like I said complete overkill and may even make the situation harder. \$\endgroup\$ – Bradman175 Nov 18 '16 at 14:22
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    \$\begingroup\$ @OlinLathrop - there are two circuits in the linked answer he is referring to. \$\endgroup\$ – Andy aka Nov 18 '16 at 14:31

Realistically you need your op-amp to have positive and negative power supplies like this: -

enter image description here

With this type of amplifier, the inputs and the output can work correctly within their power rails down to and beyond 0V. If using a single supply rail, the LM358's inputs will work down to 0V but the output will not fully get down to 0V and this gives you the offset you see. Be also prepared for your input ADC device not to fully work down to 0V on its input either.

For more circuits like this see here.

  • \$\begingroup\$ oh, the op-amp we acquired is an Tl072acp. Would this change the circuit? \$\endgroup\$ – vality Nov 22 '16 at 14:28
  • \$\begingroup\$ It should be OK providing you are not expecting great noise performance. Maybe run it at +/-10V supplies. \$\endgroup\$ – Andy aka Nov 22 '16 at 14:32
  • \$\begingroup\$ We are using an Arduino board to power the circuit, and i believe it can max put out 5V \$\endgroup\$ – vality Nov 22 '16 at 14:37
  • \$\begingroup\$ Well, you also need a negative supply and the minimum operating supply for the TL072 is + and - 5 volts. \$\endgroup\$ – Andy aka Nov 22 '16 at 15:07

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