I'm thinking of buying a portable oscilloscope to detect PWM in laptop and phone displays. I read in a website that someone uses a photo diode connected to an oscilloscope to measure the PWM of a laptop screen. But that is connected to a full size oscilloscope, which is big and expensive. There are quite a number of small and relatively affordable oscilloscope like in the links below: [Portable Mini Oscilloscope TFT][1] [Portable Oscilloscope in Amazon][2] Here is how this person detects and measure the PWM frequency: [http://www.retropcmania.com/2011/11/soundcard-oscilloscope-on-thinkpad-x61.html][3] Is it possible to create a smaller setup using a portable oscilloscope, one that I can bring in my pocket, and test out laptop displays to see if they have PWM or not, and if PWM is present, at what frequency. But I dont have much experience using oscilloscope before. Does anyone know if it can be done? Can whether can connect a photo diode to the portable oscilloscope or not? [1]: http://www.ebay.com/itm/Portable-Handheld-TFT-ARM-Digital-Storage-Oscilloscope-Pocket-Size-High-Accurate/112402223392?_trksid=p2045573.c100506.m3226&_trkparms=aid%3D555014%26algo%3DPL.DEFAULT%26ao%3D1%26asc%3D41451%26meid%3Dcdc2df1436444e48808713220aea9567%26pid%3D100506%26rk%3D1%26rkt%3D1%26 [2]: https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Daps&field-keywords=portable%20oscilloscope [3]: http://www.retropcmania.com/2011/11/soundcard-oscilloscope-on-thinkpad-x61.html

I think the only tricky part is to build a cable that's connected to a photodiode. I looked up how to do this some years ago and I was told it requires soldering skills. That was where my research ended. Probably the cheapest setup: an old headphone cable + 10K(?) Ohm resistor + photodiode + PC sound card + software oscilloscope (https://www.zeitnitz.eu/scope_en). If connected to a notebook or better netbook, it's totally portable. I also read such a cable could be connected to an Android phone, but the oscilloscope app might have to be purchased.

Yeah, that's the difficult part. The article in the link above, that guy also uses a laptop with a dedicated soundcard, plus software to measure the PWM frequency. This setup is not very portable. I was thinking of having a small pocktable oscilloscope that I can bring to the store with me to check if a laptop model has PWM or not. If the setup is too big, it would not be practical to bring to the store to quickly test if a laptop has PWM or not. But the portable oscilloscope from ebay in the link above can detect frequency, somewhat similar to laptopmedia.com's PWM testing chart. Is it possible to just attach a photo diode to the oscilloscope just like that? I google's photo diode for oscilloscope, and cant seem to find any. Maybe like you said, need to manually solder it, which if that is the only way, I will not be able to do. If someone finds a photo diode that can be connected to a portable oscilloscope like in the link above, do let me know.

[upl-image-preview url=https://i.imgur.com/oz1juIP.png] I found a setup using a portable oscillscope model DS213 like in the photo, a photodiode (Vishay BPW34) and a resistor (100kohm) in parallel [upl-image-preview url=https://i.imgur.com/wf9evQd.jpeg] I think it detects all kind of flicker

@"Alyosha2001"#p21674 I do wonder the max frequency those portable scopes can capture

Portable oscilloscope to detect PWM

Alyosha2001

JTL Something like 100 ns/div which I think is about 10MHz. However, all I know about oscilloscopes I learned 20 years ago in a class in college and since then I forgot.

But I think that's enough for what I need.

Next I want to see if I can capture any difference in the same hw with good and bad os/drivers

Alyosha2001

Alyosha2001 Next I want to see if I can capture any difference in the same hw with good and bad os/drivers

Bad news, I measured both good and unusuable OS'es and could not find any difference using the oscilloscope, no flickering on neither one.

Interesting results on a Lenovo Legion; my cousin braged about no disconfort so I measured it at full brighness, as he uses it. No flickering and easy on eyes; however, from time to time, as he opens a video (in any video player) a jitter appears around tens of kilohertz. In the browser, youtube, none.

I really thought I would find the culprit, but it appears that, although I'm using the same hw and version of ditherig, win10/11 is unusuable and 8.1 very good. Maybe i'm using the oscilloscope wrong? Has anyone measured any difference between good and bad sw on the same hw?

Seems that there is something more than dithering, or maybe ditherig.exe can no longer shut it off completely?

JTL

Alyosha2001 Do you see anything similar if you lower the brightness on a bright white background? (so not a video)

KM

Alyosha2001 a jitter appears around tens of kilohertz

Perhaps an electromagnetic disturbance from the PC itself, which could happen under sudden load. You could check for it if you cover the sensor but the signal still appears. I believe it's the blank wires that can pick up all kinds of interferences. I found I can even measure Wi-Fi signals, by holding the sensor apparatus close to a smartphone, smart TV, wireless gaming controller, etc.

I measured both good and unusuable OS'es and could not find any difference using the oscilloscope

Neither could I. The OS/GPU pixel flicker, of whatever kind exactly it is, must be incredibly small and difficult for a photodiode sensor to pick up.

Alyosha2001

JTL Only on screens with PWM such as the Lenovo Legion. On the AUO Zbook screen I use there is no flickering neither at the lowest brightness

JTL

KM Neither could I. The OS/GPU pixel flicker, of whatever kind exactly it is, must be incredibly small and difficult for a photodiode sensor to pick up.

The photodiode measures intensity of light, and largely temporal dithering doesn't result in a perceptible change of the brightness so it kind of makes sense a standard photodiode wouldn't pick it up.

Alyosha2001

JTL That's a very interesting fact! Maybe we should try an RGB photodiode. I'll ask about it

JTL

Alyosha2001 Don't know about that but I do know of some high speed camera options that would almost undoubtedly work and might not suffer from some of the issues with attempting to use a smartphone as a high-speed camera (like ISO noise or certain focus problems) and would probably be more precise. With all good things there are two problems:

1) List price of around $5-10k depending on options

2) I'm a person too busy with other things to conduct research at the moment