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Synchronizing multiple pixies over UART

Pixy Software
#1

Hi guys

I am currently combining 5 pixies to create a static motion capture system (think poor man’s vicon system). It seems to work quite well, but the problem I am currently running into is that I cannot sync the pixies such that they take pictures at the same time. I had to opt for UART over USB as the cabling distances are quite large so I cant use the linux pixy library. My hope was that by powering up all pixies at the same time they would be more or less in sync (atleast initially), but that does not seem to be the case. Is there any makeshift way I could resync the pixies in software over UART? Otherwise are they any other ways of doing this?

Thanks in advance for any help.

#2

Hey Arnold,

when you say “take pictures at the same time”, what do you mean? Pixy doesn’t support timecode or anything of the sort…what’s the time gap you’re seeing? And what do you need?

Thanks,
Jesse

#3

Hi Jesse

Thanks for the reply.

I am using the pixy cameras to do 3D triangulation of features. Ideally all cameras would expose the scene at the same time, which means when I do the triangulation the cameras are all seeing the same feature’s position at the same. If there is delay between the cameras’ shuttering and the feature is moving, there will be a triangulation error as the different cameras capture the feature position at different times.

When I receive data from the pixies on my PC I timestamp them from the system clock, and I am seeing varying differential times of up to 20ms. I was hoping that if I powered them up simultaneously that they would all initially be in sync, but that doesnt seem to be the case.

If there is some hack method to sync up pixies (at least initially), such as writing over UART to change LED brightness for example, I will gladly take it!

Any advice will be greatly appreciated.

Thanks,

Arnold

#4

Ahhh I understand. That is troublesome! Unfortunately, 20ms is a single frame in Pixy’s time - it runs at 50 frames / second.

I’m not aware of any sync method like this, but then again, I am not the expert here. Let me see if I can get Edward to hop on and bestow some wisdom.

Cheers,
Jesse