Photodiode Experiment#

PsychoPy Photodiode Experiment for Clock Synchronization.

This lsl-tool displays a simple visual stimulus (e.g., a flashing square) intended to be captured by a photodiode. Its primary purpose is to generate events that can be used to measure and correct for timing offsets (clock drift) between the stimulus presentation computer and an LSL-streaming data acquisition system (e.g., a DSI headset).

Hardware Setup#

You will need to set up a lightdiode as well as a MMBTS for this experiment. You can find instruction on that here. Make sure to place the light lightdiode on the top right corner of the screen for this experiment.

How to Run the Software#

To start the experiment, run the main.py script from your terminal:

python main.py

The script will present a menu. You can press Enter to select the default choice and begin the interactive setup.

Interactive Setup Arguments#

After launching, the script will ask a series of questions to configure the experiment. Pressing Enter without typing will select the default value shown in the prompt.

1. MMBTS Hardware Triggers#

This configures the connection to an MMBTS device for sending hardware-timed event markers.

Do you want to connect a MMBTS? (y/n):

  • y / Default: Use if you are connecting an MMBTS device.

  • n: Use if you are not using an MMBTS device.

What is the COM port for MMBTS? (DEFAULT: COM10):

  • This prompt only appears if you answered yes above.

  • Enter the COM port your MMBTS is connected to (DEFAULT: COM10).

2. Software Triggers#

This configures a software-based LSL marker stream for sending event markers directly from the script.

Do you want to send software triggers? (y/n):

  • y / Default: Creates a new LSL marker stream.

  • n: Skips the creation of a software marker stream.

Create a marker stream name (DEFAULT: PsychoPyMarkers):

  • This provides a unique name to identify your software LSL stream on the network.

Input a unique software integer trigger (DEFAULT: 3):

  • Enter a specific integer value that will be sent as the marker.

3. Experiment Parameters#

These prompts control the behavior of the photodiode flash sequence.

How many trials do you want to run? (DEFAULT: 25):

  • Defines the total number of flashes (trials) for the experiment.

At what rate do you want the flashes to run? (DEFAULT: 0.25):

  • Sets the duration (in seconds) of each flash and the pause that follows. A value of 0.25 means a 0.25s flash followed by a 0.25s pause.

At what rate do you want to offset? (DEFAULT: 0):

  • Sets a timing offset value in seconds.

4. Recording#

This option automatically records the LSL streams you have configured.

Do you want to record? (y/n):

  • y / Default: Starts the recorder (tools/consume/unified_receive.py) as a background process.

  • The recording begins just before the experiment and stops automatically after it finishes.

  • The output is saved as photodiode_exp.csv in the same directory.

Example Walkthrough#

Here is an example of a complete interaction:

Please select an option:
    1. Photodiode
Enter your choice (1): 1

Do you want to connect a MMBTS? (y/n): [PRESS ENTER]
What is the COM port for MMBTS? (DEFAULT: COM10): [PRESS ENTER] 

Do you want to send software triggers? (y/n): [PRESS ENTER]
Create a marker stream name (DEFAULT: PsychoPyMarkers): [PRESS ENTER]
Input a unique software integer trigger (DEFAULT: 3): [PRESS ENTER]

How many trials do you want to run?(DEFAULT: 25): 10
At what rate do you want the flashes to run? ( DEFAULT: 0.25): [PRESS ENTER]
At what rate do you want to offset? ( DEFAULT: 0.0): [PRESS ENTER]

Do you want to record? (y/n): y

Outcome of this example#

  • The experiment will connect to an MMBTS on COM10.

  • It will create a software LSL stream named PsychoPyMarkers that sends the integer marker 3.

  • The photodiode will flash 10 times with a 0.25-second rate.

  • The recorder script will launch in the background, recording both the hardware stream and the PsychoPyMarkers into a file named photodiode_exp.csv.

An analysis can be ran on the file created by this experiment. You can find it on the next page.