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H7 image "blown out" by IR LEDs

Posted: Thu May 21, 2020 11:54 pm
by kwiley
If I turn on the IR LEDs on my H7 (default sensor and lens), the live preview image in the IDE loses practically all contrast. It's a wash of gray showing just the barest ghost of an image of the scene (if I point at literal lights or the computer screen, the image comes through, although washed out). Now, the initial suspicion would be that the sensor is EXCEEDINGLY sensitive to IR and that I the LEDs are actually blowing the sensor out of the water.

But that can't be the case. First of all, my M7 behaves normally, with the IR LEDs simply brightening up the image a little bit. But it has a different sensor, so that could explain the difference. They also have different LEDs, so again, maybe that's the difference.

But I left the H7's LEDs off and then pointed the M7 at the scene with its LEDs on, and the H7 preview image didn't go to hell. It was just slightly brightened by having the M7's LEDs pointed at the scene. But still, one could argue that the H7's LEDs are insanely more powerful, so maybe that's the explanation.

But then I turned on the H7's LEDs and the live feed, once again blowing out the image, and then covered the LEDs with my fingers, careful to do a good job really covering them up. And the image did not improve. Pointedly, even if a little IR light was leaking out, the image didn't improve a little bit, to be honest. At this point, I'm convinced there is a hardware or software error occurring. This error only seems to occur with the IR LEDs. The RGB LEDs (or three color single LED, whatever it is) doesn't do this.

Is the circuit to the IR LEDs (which are physically a different object than the RGB LED) doing something to the sensor circuit?

I've attached some screenshots.

Thanks.

Re: H7 image "blown out" by IR LEDs

Posted: Fri May 22, 2020 12:34 am
by kwagyeman
I think it's a hardware issue related to IR light going through the bottom of the camera board into the bottom of the sensor.

You can fix this by putting black electrical tape under the sensor. The M7 had a similar issue when sunlight hit the back of it. We had fixed that with a black sticker. But, the H7 has no such place to easy put one on.

Re: H7 image "blown out" by IR LEDs

Posted: Fri May 22, 2020 2:12 am
by kwiley
I appreciate you theorizing as the problem, but are you saying I have discovered this issue a year after the H7's release and there is next to no discussion about it on the boards? I can't be the first person to run up against this. How do you deal with this exact same issue on your own H7s, of which I imagine you must have tons spilling out of drawers?

Re: H7 image "blown out" by IR LEDs

Posted: Fri May 22, 2020 8:31 am
by iabdalkader
kwiley wrote:
Fri May 22, 2020 2:12 am
I appreciate you theorizing as the problem, but are you saying I have discovered this issue a year after the H7's release and there is next to no discussion about it on the boards? I can't be the first person to run up against this. How do you deal with this exact same issue on your own H7s, of which I imagine you must have tons spilling out of drawers?
It's a known issue and has been discussed before, we decided to leave the IR LEDs anyway as they cost nothing and might be useful with some other sensor or with the extension cable. You could try the extension cable or build something like this and control with the a single I/O:

openmv-proto-shield_1_5.jpg

Re: H7 image "blown out" by IR LEDs

Posted: Fri May 22, 2020 11:16 am
by kwiley
Okay, so long as I don't have a defective unit. That was one concern of mine. If it's systemic to the design and you're already aware of it, then don't worry about it. Thank you for the various suggestions. I'll mix them all into an eventual solution.

Cheers!

Re: H7 image "blown out" by IR LEDs

Posted: Fri May 22, 2020 2:19 pm
by kwagyeman
People haven't really been complaining that much about it. Other things to fix, so, we don't worry about it.

Also, it's not really an easy to fix issue. The IR light easily goes right through material that looks opaque to visible light. Black electrical tape works if you need a quick solution.