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.

    martin I'm not sure. I hope so. I didn't encounter any high speed PWM yet.

      KM What was the highest freq you measured with it? Mine was 20khz with the soundcard, but the actual graph seems off, so not sure.

      • KM replied to this.
        14 days later

        martin No more than 240 Hz yet. I find the soundcard solution to be much more responsive. It even picks up my ceiling's 100 Hz incandescent flicker from afar while the Hantek oscilloscope receives a flat line. Maybe the photodiode needs an additional external voltage. The audio cable somehow might supply that voltage.

        2 months later

        martin my setup is enclosed in a case so it's not easy to photograph. I started off with a cheap Amazon USB scope but found that I was hitting the limits pretty easily. My present scope was rather expensive and does an actual 500 MS/s so it won't ever be the weak link.

        The special sauce is having a really clean power source and then adding a 100,000 ohm (or higher) resistor to amplify the fluctuations coming out of the diode. Also, be certain that the diode's switching rate is sufficiently fast to capture the frequency you're looking for.

        7 days later
        3 months later

        I got all the components, and did very bad solder work. To my surprise, the oscilloscope detects light input. But it's no better than the BPW34 yet. I can't get the 9V battery to work. I hold one end at VCC and the other end to any of the two probes, but the signal won't get amplified. Also the first signal was negative, so I had to swap hook and grapple. I don't know how to make progress. It seems impossible for an average person. I believe without the battery it won't detect any higher frequencies.

        5 days later

        valex13 The price looks good but they don't say anything about the sample rate, which seems suspicious. It could be anything. Am tempted to buy it, but where's the detailed data sheet?

        Edit: Found some offers on eBay in which the sellers claim the sensor operates at 6000 Hz. That would be way to little for our purposes.

        Wootever How would one know the correct orientation when inserting the OPT101 into the CJMCU-101? I have another set of parts but the next time I want to do everything right. And how did you know where to put the red and black battery cable before soldering them? It seems those two tasks, apart from decent soldering, are the most important ones.

        I just fried my 2nd OPT101 by connecting the 9V battery. The sensor got pretty hot and then ceased to function. Pretty frustrating. Don't know what to do now. Maybe this approach is a dead end.

          9 days later

          If anyone still reads here, in a final attempt to measure anything useful I bought the handheld flicker meter Fauser LiFli ($300), and maybe the most important thing I found out so far is that flicker-free monitors do flicker, although very little, and even at 100% brightness. My two BenQ EW2740L flicker at 2% and the totally unusable Dell U2515H flickers at 4%. Still doesn't explain why one of the BenQs is not perfectly usable. Maybe very small differences in percentage make the difference. But 2% is the least you can measure with this device. My cheap Hantek 6022BE oscilloscope which I connected to the LiFli seems to suck too much to pick up such small differences. Currently I'm not willing to spend any more money for a better oscilloscope. I have an LED bulb that flickers at 4% when you turn it on and then it slowly continues down to 0% over some minutes. During the first seconds I get PWM symptoms. Later this LED is much better. So it seems the safe percentage for me might be somewhere between 0% and 2%. Which is insane since we're talking of frequencies between 20 kHz and 400 kHz. However, even this 0% LED is still buzzing slightly, made audible by the LiFli device's speaker. So there still is some ripple. It seems true flicker-free is not possible with wall-plugged devices. My small LED battery-driven flash light is at 0% without any buzzing.

          I didn't measure flicker percentage (a-b)/(a+b) but ripple percentage (a-b)/a, which makes more sense to me.
          Where a is max and b is min voltage.

          https://www.fauser.biz/li/lifli_e.htm

          Edit: With my new oscilloscope setup (a few posts below), it turned out that the low percentages (like 0-2 %) the device measured was probably the display's 60 Hz refresh rate flicker. I did not even know that LCD matrixes would pulsate at each refresh when displaying a constant image, but apparently they do.

          The 6022BE has much trouble with low voltages:

          In the picture you can see a ripple of roughly 20%.
          To me it looks like it is impossible to spot amplitude differences of 1% and even below, which seems necessary. Can any oscilloscope do this actually? If anyone knows how to amplify the signal before it enters the oscilloscope (it is a 3.5 inch audio to BNC cable), please let me know. Preferably with some purchasable device.

          11 days later
          10 days later

          @martin and anyone who is interested: With the help of the above link I managed to make my BPW34 very responsive for oscilloscope use. Older posts here helped me too, like TechSensitive mentioning a 100,000 Ohm resistor.
          I also bought another oscilloscope, the PicoScope 2204A. It is their cheapest oscilloscope for ~140 € and does the job. They have excellent online support and replied to my questions in detail, recommending this model. In fact I do not understand why I had to search that long to find PicoTech when it seems to be the best USB oscilloscope manufacturer.

          This is how I made the BPW34 responsive:


          Note how the BPW34 has a dot on its detector surface, pointing to the end that gets connected to the resistor. It is a 100K resistor. The hook and grapple hold the resistor. The grapple also holds the black battery cable, negative pole (-).


          The battery's positive pole (+) goes directly to the BPW34.

          I do not know the maximum frequency that this setup can measure. The BPW34 PDF says the maximum responsivity is 100 ns with 10 V and 1K resistor. A 100K resistor amplifies the current voltage so it is easily detectable by the oscilloscope, however it may make the diode less responsive.
          However, with this I measured 200 kHz very low amplitude ripple on my "flicker-free" monitor, so there is that. Anyone has an idea what the limits of this setup are?

            sounds like a good project for my cheap hantek usb o-scope

            KM Im happy to see this thread lives on and the oscopes we can create are improving. I lost track of it but Id like to get back to it. I have Hantek 6022BE and a batch of few of these LEDs with the small circuit. Your new setup seems a lot simpler to make. Can you recommend any good freeware software for the Hantek?
            Ill get around getting these parts and see what I can make of it🙂

            • KM replied to this.

              martin Not sure what the best software is, but the OpenHantek software is pretty limited. I have a feeling the most developed software is HScope for Android, followed by some Windows 3rd party programs (which I did not try).

              Today I tried to attach longer cables to my setup but it actually led to more noise and a worse signal. It is probably a good idea to keep everything as simple and short-cabled as possible.

              martin Good news: With the current setup I can detect 10 MHz PWM (and even more). It is a little out of shape, but clearly visible. And this was just the PWM of a small pin LED. A monitor is much brighter and should deliver even better results.

              • JTL likes this.
              17 days later

              valex13 I purchased the Radex Lupin. It works great for older laptops (like 5+ years old) as well as cars (even new cars). It also works great for detecting flicker in LED bulbs (I found that I was getting headaches, etc., from some LED bulbs that I had purchased). For me, LED bulbs below 5% flicker are just fine. Anything above, say, 30% flicker will cause noticeable problems. Anything in between is hard to say. I ended up walking around my house and replacing many of my LED bulbs with ones that flicker less.

              KM I am very tempted to purchase the Lifli. It's totally worth the money to me if it works. I just don't want to waste $300+ on something that doesn't do what I want it to do. Would you say it does what's advertised? Specifically, will it detect PWM in newer laptops? I understand that it's not very precise because it only has 18 LEDs to indicate the amount of flicker.

              • KM replied to this.
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