Pyxid2 sends unwanted messages when sending two messages very close in time

Hardware General
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1

Hi!

I am using a Cedrus C-pod connected to a BrainVision USB-Adapter to communicate and send triggers to the BrainVision Recorder. I am using the pyxid2 library to send the triggers via a python script.

When recording, some unwanted and unsent messages appear (S246 ans S254 mainly), doing some research, I have arrived to the conclusion that they are sent whenever two of my messages are sent very close, but not always. As in my script events happen very close I need to send the triggers very close too. They do not even follow a periodic appearance or any behaviour to know certainly why they are sent. I have seen that the S254 message is to clear one line.

The problem is that sometimes they override my messages (probably because they arrive almost together), so it becomes a big problem.

Is there any way to tell to pyxid2 that it can not send messages by its own or to avoid this problem?

Thank you.

2

StimTracker can send event markers autonomously. However, with c-pod, events can only be sent using your own code.

pyxid2 cannot send messages on its own. It’s a library at your disposal; it sends event markers only when you ask it to.

Please clarify the question or send us an email to arrange for a zoom meeting.

3

Sorry the late answer.

Briefly, the problem is that messages S246 and S254 appear in the recordings of the data, but I do not send them through my code.

4

I have no experience with BrainVision Recorder. I will take a guess though assuming that S246 and S254 represent trigger input values.

S254 would correspond to these bits:

1111 1110

In other words, one of two things are happening:

  1. You have set the upper 7 bits, or most likely,

  2. You have set the lowest bit 0, but somewhere along the line this is being interpreted as negative logic instead of positive logic.

c-pod firmware version 2.2.7 added the capability to produce signals using negative logic because some EEG systems require it. You can check this setting using our Xidon 2 software.

However, it is also possible that there is a setting in BrainVision Recorder that makes it interpret triggers using negative logic.

As for S246, it corresponds to these bits:

1111 0110

This corresponds to six bits that are set simultaneously (less likely) or two bits (0 and 3) that are set and negative logic being used.

Again, these suggestions are based on an assumption about what S246 and S254 mean! I hope they help.