martin The BPW 34 seems to be pretty fast. 100 nanoseconds rise/fall time for the Vishnay Model, 200 ns for OSRAM's. I found this link where someone further explains those values: https://electronics.stackexchange.com/questions/118141/high-frequency-blinking-leds-and-sensor-for-that

The OSRAM BPW 21 you mention seems to be much slower - 1.5 microseconds, which are 1500 nanoseconds:
https://www.osram.com/os/ecat/TO39%20Ambient%20Light%20Sensor%20BPW%2021/com/en/class_pim_web_catalog_103489/global/prd_pim_device_2219533/ (There's a linked datasheet PDF with specs)

OSRAM BPW 34:
https://www.osram.com/os/ecat/DIL%20BPW%2034/com/en/class_pim_web_catalog_103489/global/prd_pim_device_2219534/

The next step might be those more expensive photodiodes. Somewhere I saw a price of $40. But maybe that's overkill. We better upgrade our oscilloscope first.

The cheap Hantek 6022BE USB oscilloscope has sample rates of up to 48 MSa/s. Compared to 44100 Hz of our sound card, that'd be a big upgrade.
www.amazon.com/Hantek-HT6022BE20Mhz-Digital-Oscilloscope-Bandwidth/dp/B009H4AYII

It even has an open source project with Linux and Mac support: http://openhantek.org

      KM That Hantek one looks good, I might buy it. However, do you know how to attach the photodiode to it? Seems like a completely different cable.

      • KM replied to this.

          KM Might be. @TechSensitive , could you shed some light on this? Just a photo of how your setup maybe looks like with a small explanation how the photodiode is attached, would help a lot.

              martin I got the oscilloscope today. It has a "crocodile" and a hook connector:

              Short impressions so far:
              - The output is more accurate than (my) sound card oscilloscope. One can actually see the "zero" axis and judge how big the difference in amplitudes is. Plus the waves resemble reality much better.
              - The Hz counter of the OpenHantek software is worse than the sound card scope. It seems to count only very obvious sinus waves. I.e. when the PWM almost touches the x-axis. Not sure yet how to change that.

              Result of OnePlus 3 PWM at zero brightness:


                Amazing. Could you test some of the newer iphones, in case they give you eyestrain as well? Im gonna do that on my work iphone where I have absolutely terrible and long lasting pain.

                Yes the software looks crap compared to Zeitnitz. Also we might need to get a better photodiode just to be sure. I was recommended this - https://www.conrad.cz/pin-fotodioda-osram-components-bpx-61-to-39-vyz-uhel-55-400-1100-nm.k153122

                @Wootever please what is the difference when you use the diode with the circuit as bought from ebay?

                  martin
                  The transimpedance amplifier converts current from the photodiode to a voltage usable by the oscilloscope (it basically amplify the signal for a more stable output).

                  The advantage of a combined/embedded design:
                  The integrated combination of photodiode and transimpedance amplifier on a single chip eliminates the problems commonly encountered in discrete designs, such as leakage current errors, noise pick-up, and gain peaking as a result of stray capacitance.

                      Wootever Thank you, that is amazing. And it can be clipped to the oscope probes like the regular diode? Could you show a photo of how it is attached to the oscope so it works? I will order it from your link.

                          Wootever Thank you, so I just connect the probe tip to the middle two, probe ground to the bottom two and it will work? What about the voltage supply? (Red)

                              martin
                              Voltage supply is needed for the transimpedance amplifier, but the power consumption is very low, a single 9V battery probably lasts for months/years.

                              Edit:
                              Here are a few example photos of a basic OPT101 photosensor:

                              Galaxy S8 AMOLED PWM on 10cd/m2:

                                  Wootever Thank you, that is exactly what I needed. Im on to get better readings then🙂

                                    9 days later

                                    For Android there's an app called "HScope". It supports various Hantek devices, including the 6022BE. My first impression is that it's great software. It detects frequencies much better than OpenHantek does and generally seems very polished. We might be able to create a portable solution with an Android device, a USB On-The-Go cable, a power bank, 6022BE + probe, and the HScope app.

                                    HScope App: https://play.google.com/store/apps/details?id=com.martinloren.hscope
                                    Guide: http://hscope.martinloren.com

                                    • JTL replied to this.

                                      KM Very cool. How much does said Hantek oscilloscope cost?

                                      • KM replied to this.

                                          JTL $63.49 @amazon.com

                                          • JTL replied to this.

                                              KM Not bad. Do you know the highest frequency/sample rate it can capture?

                                              • KM replied to this.
                                                  5 days later

                                                  KM Does the sample rate matter much? I read hantek 6022be range is 20Mhz, will it therefore display properly any PWM that might be in that range, like new macbooks 100khz?

                                                  • KM replied to this.
                                                      dev