saving video on SD card

OpenMV Boards
41
  • The total capacity on OpenMV is less than 100K, which is NOT enough to save ANY video, an SD card is a must for video recording (BTW, what is the MAXIMUM SD card capacity that OpenMV is able to support? )
  • Is there a way or the need to specify SD card location? For instance, we ALL know that
log = open('.log.csv', 'w')

will write a log file log.csv just under the same folder as main.py. Is there a folder specifically for SD card?

  • How to view the contents inside the SD card when the SD card is plugged in OpenMV board? I now have my SD card formatted into EXT4. Which file format is OpenMV able to load/see on the SD card?

Thank you very much
Pei

42

It looks I’ve found something here OpenMV Cam M7 first look - Elmwood Electronics , cited in the following:

  • OpenMV only works with FAT.
  • Max readable SDHC card value is 32G
  • If the camera saves a picture to the SD Card while mounted on a pc… the PC won’t see the photo without remounting the drive as it assumes USB flash drives can’t magically create files on their own (which is usually true 99% of the time).

What’s more (cite):

3 ways OpenMV will mount as a USB device :

  • Only internal on board memory (no SD Card) : 2 Megs
    Will appear as a standard USB drive.
    Contents will be ‘Main.py’
  • With MicroSD card inserted on board :
    To capture any images or video you have to insert a microSD card.
    You won’t get a warning until the runtime file tries to save a file.
    This will now supplant the internal memory and be the default usb drive you see.
    When you plug in the OpenMV, you will no longer see the internal 2 Meg memory mounted to the desktop.
    Only the Camera SD Card will now mount to desktop.

However, according to my test, both M4 and M7 does NOT come with 2M on-board memory, but much less than 100K.

568×562 36.1 KB

568×562 36.1 KB

Finally, how to show up the SD card’s contents when the SD card is plugged in OpenMV board, which is USB connected to the laptop?

Thanks

43

The 2MBs cited is the whole flash size, a large part of the flash is used for the firmware image. The internal/flash file system is around 100KBs. I don’t understand your second question, just connect the SD card and connect the camera via USB and the SD card will be mounted.

44

Thank you iabdalkader…
Yeah, it’s quite weird that when I plugged in my SD card, nothing shows up…

  • Should I format the SD card in advance to some particular file format?
    Currently, my 32 HC Micro SD card comes with ext4 …
  • Otherwise, should I flash something onto the SD card before inserting into OpenMV? I think it should be OK for me to just leave the SD card empty, right?

Cheers
Pei

45

We support FAT and exFAT. Most microcontrollers only support these formats.

As for files not showing up on the PC when recorded… there’s no way to fix this. Modern OSes don’t mount the USB flash drive like a network disk, they think they have full control and mount the disk on as a block device. It’s very easy to loss data if the PC and the OpenMV Cam are accessing the flash drive at the same time when this is the case.

Anyway, unless we can change the driver code that scans USB drives on Mac/Linux/Windows you just have to reconnect the device again for the PC to rescan it.