Photodiode Experiment#

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 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 MMBT-S (a device used for sending hardware event markers in neuroscience experiments) for this experiment. You can find instructions on that here or visit the MMBT-S documentation. Make sure to place the 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.

1. MMBT-S Hardware Triggers#

This configures the connection to an MMBT-S 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 experiment#

  • 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 run on the file created by this experiment. You can find it on the next page.