Portable oscilloscope to detect PWM

Kray

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
Portable Oscilloscope in Amazon

Here is how this person detects and measure the PWM frequency:

http://www.retropcmania.com/2011/11/soundcard-oscilloscope-on-thinkpad-x61.html

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?

KM

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.

Kray

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.

Alyosha2001

I found a setup using a portable oscillscope model DS213 like in the photo, a photodiode (Vishay BPW34) and a resistor (100kohm) in parallel

I think it detects all kind of flicker

JTL

Alyosha2001 I do wonder the max frequency those portable scopes can capture

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