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Oscilloscope and Photodiode for Testing PWM
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

Oscilloscope and Photodiode for Testing PWM

by Robgoren on Fri Jan 01, 2016 8:24 am

Hi,
I'm extremely sensitive to the PWM flickering on most laptop and tablet screens. PWM, or pulse width modulation, is the process by which the backlight is pulsed on and off rapidly to simulate the brightness of the screen in lieu of using a proper dimming circuit. I would like to test for PWM on a variety of screens and was curious to know which of the oscilloscopes advertised on the adafruit site would work the best. Also, where would I get a photo sensor to attach to the screen?
Many thanks!!

Robgoren
 
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Re: Oscilloscope and Photodiode for Testing PWM

by adafruit_support_rick on Fri Jan 01, 2016 1:41 pm

PWM is comparatively low-frequency. That's why you can see it. Any oscilloscope can resolve PWM frequencies in that range.

Unfortunately, we don't have any visible-light phototransistors in the shop.

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Re: Oscilloscope and Photodiode for Testing PWM

by Disciple on Fri Jan 01, 2016 4:26 pm

Last year I acquired an ultra low-cost USB-type oscilloscope, and measured pulses using a common LED as a sensor. It was an IR LED to measure the pulses of a remote control clicker, but it worked surprisingly well, and I read that visible light LEDs can do the same trick. Just an idea.

Hallelujah!
Disciple
Last edited by Disciple on Fri Jan 01, 2016 4:38 pm, edited 1 time in total.

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Re: Oscilloscope and Photodiode for Testing PWM

by adafruit_support_bill on Fri Jan 01, 2016 4:31 pm

That is correct. An LED can be used to sense light. There are some tutorials on it here:

http://makezine.com/projects/make-36-bo ... ect-light/
http://playground.arduino.cc/Learning/LEDSensor

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Re: Oscilloscope and Photodiode for Testing PWM

by adafruit_support_rick on Mon Jan 04, 2016 12:00 pm

This just showed up in the store. It should be fast enough for PWM frequencies:
https://www.adafruit.com/products/2748

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Re: Oscilloscope and Photodiode for Testing PWM

by Robgoren on Sat Jan 16, 2016 8:34 pm

Awesome! Thanks for all your helpful replies.

Robgoren
 
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Please be positive and constructive with your questions and comments.