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photodiodeStressTests

Script description:

This repository hosts a code to run a photodiode stress test with PTB: This test flashes a square at the corner of the screen on and off at different frequencies. The luminance value of the square is also varied. The aim of this script is to stress test photodiode recording devices to see if they are able to keep up with super fast flashing and whether the gain of the photodiode recordings is sufficient to discriminate the flashes from background noise at different luminance values

Test structure:

The test consists in flashing the photodiode square on an off first every frame, then every second and then every third frame. In each phase, the photodidoe is flashed a set amount of times depending on the value passed to the function. This sequence is repeated for different photodiode square luminance values. The luminance of the square decreases in a stepwise fashion according to the set luminance decrement factor.

How to use:

Open matlab and in the command window, enter:

  • runPhotodiodeStressTest(LumDecrement, PhotodiodeSize, debug) \nParameters:
  • flashIterations: how often the photodiode should be flashed
  • LumDecrement: number between 0 an 1, representing the steps of luminance decrease during the test. If set to 0.25, the first block will present photodiode at luminance 100%, second at 75%, third 50%... Default: 0.25
  • PhotodiodeSize: size of the photodiode square in pixels. Default: 200
  • debug: when set to 1, the experiment will be run in windowed mode, PTB sync test will be skipped. Default: 0

Outputs

The test outputs a csv table, containing information about what happened. The output csv can be found in the directory ./data The table are in the following format:

Output csv:

Date FlipRate EventNumber Onset Event
Date of the run How often the photodiode is turned on Number of the current event Timestamp of the photodiode onset Photodiode status (on or off)
--- --- --- --- ---

Recommandation:

While this script varies the luminance of the photodiode square on screen, this is not equivalent to manually changing the brightness of the screen in the systems settings. It is therefore recommended to repeat this test several times, changing the brightness of the screen in a stepwise fashion

Standard operation procedure:

Here is an example of the procedure we followed to test it in our lab:

Setting up the computer:

  1. Once the laptop is turned on, hit the windows button and type in "Display settings"
  2. In the display settings, set the **"Adjust brightness level" to max (100) **
  3. Open matlab

Testing the photodiode:

  1. In matlab, navigate to the directory of the runPhotodiodeStressTest.m
  2. In the command window, type in the following:
    • runPhotodiodeStressTest(1000, 0.25, 400)
  3. The experiment should start and inform you that you should have the photodiode plugged in and that it should be on top of the photodiode square.
  4. Hit any button once you made sure 4. is met
  5. Let run the experiment (~12min)
  6. Once the experiment is over, open the display settings again and set the brightness level to 80
  7. Repeat 1. -> 6.
  8. Once the experiment is over, open the display settings again and set the brightness level to 60
  9. Repeat 1. -> 6.