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I have a couple questions related to the same home project. I am brand new to circuits and have just started reading into photo diodes.

Q1: I have a home project goal to essentially get a photo diode to distinguish the different colors of LED lights I am emitting onto it. However, my main issue is that it just doesn't output any current at all. I found that the intensity of the LEDs are very weak after shining my phone LED light which has an incredible intensity but still only produced 0.01 pA. Given that I know there is no way I can increase the intensity further on the LEDs (Already burned a few out trying), is there a way that I can amplify the current output? I would like to try to get at least in the mA range.

Q2: Is there a way to use the photo diode to distinguish the LED frequencies and say convert them into different voltage outputs? I want to connect it to an Arduino and have the Arduino read either voltages or currents (Based on input frequencies), then be able to read out the frequency of light. (Another question directly involved in this) -> If I do this and the photosensitive varies based on frequency, what can I do to account for this? I attached a graph of the photosensitive diagram. For reference, I am using a Hamamatsu S1336-18BQ photo diode.

Graph

Sophia
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    Attach your circuit diagram for Q1. A photodiode cannot read out the frequency of light, instead they tell you the intensity (quantity of light), so answer to Q2 is a simple No. – user1850479 Feb 12 '22 at 06:31
  • @user1850479 Thank you for the response. I wasn't aware of this for Q2. That's unfortunate, however, I still see that I can probably accomplish the goal I have in mind with just showing the diode various intensities of the same wavelength of LED light. For Q1, all I am doing is hooking up both leads of the diode (While grounding one end of course) to an oscilloscope. I read online that the scope should simply be able to read the current its creating without any additional power supply. – Sophia Feb 12 '22 at 07:39
  • There is two ways to use photodiode: direct polarity and reversed. Most of photodiodes sensitive to infrared, but if you found visual light sensitive, use a few diodes, one with filter for each color. – user263983 Feb 12 '22 at 08:26
  • This photo diode, I at least thought is sensitive to the visible range of light. At the very least I saw that it can detect visible light and the photosensitivity seems high (From looking at the graph), but it was my first time purchasing one, so is a peak photosensitivity of 0.5 not high? – Sophia Feb 12 '22 at 09:18
  • Try using a phototransistor. They have much higher sensitivity, 100-1000 times more current output than a diode, but they only work in photoconductive mode, and they are slower, so many kHz rather than many MHz. As an example (and not a product recommendation) I use a TETP4400 made by Vishay. Cheap, relatively uniform visible light sensitivity (much more uniform than your photodiode), fast enough to a see a LED being PWMed at 50 kHz, biased with a 1.5 V AA battery, 1 mA output 200 mm from a 470 lumen 5 W domestic LED lamp. – Neil_UK Feb 12 '22 at 13:42
  • A transimpedance amplifier can amplify the current, producing an output voltage. 0.01 pA? Really? Get a more sensitive photodiode. 2) Use a prism an a beam splitter (see Floyd,Pink (1973) for details) Move the photodiode in a path across the beam, recording output at each position.
    • –  Feb 12 '22 at 14:01
  • You can't actually measure 0.01 pA of current with an oscilloscope, so you are leaving out some details or not measuring correctly. Photodiodes convert photons into electrons, and 0.5 A/watt is close to 100% efficient conversion in the visible, so you are already turning nearly every photon into an electron. – user1850479 Feb 12 '22 at 14:35
  • @Sophia Your test setup of photodiode into oscilloscope is valid. A RED light emitting diode was used for a photo-diode; connected to an oscilloscope's 1MEG input produced 30mV DC when pointed outside in daytime. That's 30 nanoamps. – glen_geek Feb 12 '22 at 15:04
  • There is no way to answer this question without knowing what circuit you tried. Please include a schematic in your question. – The Photon Feb 12 '22 at 15:44
  • @ThePhoton Here is a diagram of what I tried: https://imgur.com/a/pZylb5H – Sophia Feb 13 '22 at 02:12
  • @Neil_UK Oh that seems much more promising for sure! Thank you so much for the recommendation! I will buy a few and try those out. I do have a preference to be able to detect individual, light pulse of only 0.25 micro-seconds across. Are there any of phototransistors that could accomplish that or would that only be a job for the photodiodes? – Sophia Feb 13 '22 at 02:15
  • @user1850479 Please see the circuit diagram I attached in and earlier comment. This was just how I was trying to measure the current. I am not sure though if this is an incorrect method. – Sophia Feb 13 '22 at 02:17
  • @user_1818839 Thank you very much for the reference! I will check out their methodology! – Sophia Feb 13 '22 at 02:18