Lighting Condition for Optical Flow Breakout Board

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sean112
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Joined: Thu Nov 14, 2019 1:51 am

Lighting Condition for Optical Flow Breakout Board

Post by sean112 » Fri Dec 06, 2019 2:26 am

Hello,

I bought an optical flow breakout board for my mobile robot. Since I put it on the rear side of my robot close to my chassis, and sometimes the mobile robot blocks the light source, I put a LED right by optical flow breakout board. However, it seems like the board sometimes gives random reading after sometime. If I turn off the LED, the board will work for a while then give random reading again. Every time the board stops working, I just switch off/on the LED light, it will work for another period of time. Is there an illumination value that I should follow for this camera? I wonder if the camera auto adjust its exposure time.

P.S. The LED I have is very bright.

Sincerely,
Sean



arnaud
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Joined: Tue Feb 06, 2007 12:36 pm

Re: Lighting Condition for Optical Flow Breakout Board

Post by arnaud » Mon Dec 09, 2019 2:59 pm

Hi,

I have not observed this exact problem before. The flow sensor has an auto exposure mechanism, so this is what might be happening there. There is two things I can think about:
- The flow deck does not require high level of illumination. So one things to try would be to reduce the strength of the LED (without PWM if possible).
- How far is the sensor from the floor? The flow sensor is designed to be used no closer than 8cm from the floor, otherwise the lens will give blurry images to the sensor.

sean112
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Joined: Thu Nov 14, 2019 1:51 am

Re: Lighting Condition for Optical Flow Breakout Board

Post by sean112 » Wed Dec 11, 2019 7:34 pm

Changing the illumination method solved the problem. The LED was too bright after all.

sean112
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Posts: 6
Joined: Thu Nov 14, 2019 1:51 am

Re: Lighting Condition for Optical Flow Breakout Board

Post by sean112 » Wed Dec 11, 2019 7:34 pm

Changing the illumination method solved the problem. The LED was too bright after all.

arnaud
Bitcraze
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Joined: Tue Feb 06, 2007 12:36 pm

Re: Lighting Condition for Optical Flow Breakout Board

Post by arnaud » Thu Dec 12, 2019 6:37 am

Great, thanks for the update!

sean112
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Joined: Thu Nov 14, 2019 1:51 am

Re: Lighting Condition for Optical Flow Breakout Board

Post by sean112 » Thu Dec 12, 2019 10:41 pm

Just one quick question about the board. I believe it is still a feature extraction between two consecutive frames? Does the board take snapshot independent of the delay command in the tutorial? I am just wondering if there is anything to look out for if I decrease the delay, since I want to run as fast as it can.

arnaud
Bitcraze
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Joined: Tue Feb 06, 2007 12:36 pm

Re: Lighting Condition for Optical Flow Breakout Board

Post by arnaud » Fri Dec 13, 2019 7:04 am

The flow sensor works fast (I cannot remember how fast but I thinks its ~1KHz) and the chip accumulates movement in counters. So if you read faster, you should expect smaller readings from deltaX/deltaY counters.

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