Global shutter - oddities during capture

1 out of 50 times I make snapshots for 5 seconds the following happens from the start or during the capture:

  1. interference which seems like static noise . Typically like a curve of pixels that just take in random values

  2. 1 frame actually looks like two half frames . Half of the current frame and half of the last frame .
    They are side by side horizontally.


QQQVGA greyscale with fixed exposure time (5000us)
Wait 200ms before I start while loop.
Recording to SDRAM and snapshots with copy to fb =true

Happens with and without windowing on a certain roi.

Openmv h7 plus

After every video capture run of about 5 seconds the openmv is reset through its reset pin by another device.

Hi, could be power or signal integrity issues.

A quick fix is to disable triple buffering.

Do set_framebuffers(1) right before your main loop and you call snapshot.

Two buffers being merged means that lines are being dropped by the dcmi code. This code has been well debugged however. So, this won’t happen unless there’s some issue with the system stability.

Looks like you are running at a low res with a short exposure….

The timing configs on those smaller resolutions are tricky and they might be too fast.

A better fix will be to edit the about of horizontal line time the camera has for that resolution. I can give you the register write command in a bit for that.

So, here’s how horizontal line time is calculated:

And vertical time:

And then they are written to these registers:



If you just read back those registers using the sensor.__reg_read(), then build up what was written and then write back a larger time value (using sensor.__write_reg(, ) your error should go away.

It’s entirely possible that at the QQQVGA resolution the camera is outputting data too fast for the H7 Plus to keepup.


Wait, you asked about the global shutter sensor. Not the OV5640.

The global shutter sensor is slow compared to the OV5640. There should be no problems with it.

My initial comment about voltage/current and signal quality stands. How is the camera connected to the board? Does the board have good power input?

I have the issue both with flex pcb adaptor and when the sensor is directly on the board. I scoped the power supply (input to board) but didn’t manage to have a scope on in the rare occurrence of the issues I mentioned in my post. The voltage is very stable.