Flora Color sensor

[noanalyst]

Hi,

I am about to order the flora color sensor (PID 1356) and I have a couple of questions,

1) As I mentioned, my application will be in the dark so there will not be any ambient light to block out. Will it still work? The videos all seem to show it being tested in bright light conditions.
2) If it will work in dark conditions, is there a way I can dim the LED cause I would rather have the LED dim than super bright.

[adafruit_support_bill]

It will work in dark conditions. In fact, it will be more accurate without any ambient light.

There is no way to dim the LED itself. You could cover it with some smoked acrylic or similar filter to reduce the light output.

[noanalyst]

I assume it would be trial and error to see how much the LED can be blocked withOUT losing accuracy. Correct?

Last question. What is the smallest area that can be measured by the sensor? To get that area, must I move the sensor extremely close?

[adafruit_support_bill]

Yes. You will have to experiment to fine light levels that work. The intensity of the reflected light will be inversely proportional to the square of the distance, so longer distances will require higher light levels.

There is no minimum size. The sensor has about a 180 degree field of view as I mentioned in your previous thread. The sensitivity is approximately proportional to the cosine of the angle as shown in the data sheet. If there are other reflective surfaces within the field of view, they can influence your readings. You may need to mask those areas to avoid that.

[noanalyst]

Unfortunately in my application, I do not have that option of masking the surrounding areas, can I reduce the field of view by building a wall around the sensor so it only sees what is ahead of it. If I can how high should the wall be to measure an area 3mm x 3mm

[adafruit_support_bill]

You could restrict the field of view with a shroud. The height required would depend on the distance to the measured area.

Another option is to use a lens so the image of the 3x3mm area is focused directly on the sensor.

[noanalyst]

Hmmm, the lens option sounds like a good idea. What type and size of lens am I looking at? Do I put it right over the sensor?

[adafruit_support_bill]

Lens choice would depend on working distance and how much space you have available. You don't need anything fancy, a simple magnifying glass will work.

[noanalyst]

Ok. I will look for one online. Now the idea is that the image of the area I want should be reflected on the sensor. So the lens should be the size of the sensor. Correct?

Should I be concerned if it is a real image or a virtual image formed by the magnifying glass?

[adafruit_support_bill]

You need a "Real" image: http://en.wikipedia.org/wiki/Real_image
A larger diameter lens will be able to focus more light onto the sensor.
To form a 1:1 size image (3mmx3mm) on the sensor, the distance from the object to the sensor would need to be 4x the focal length of the lens and the lens would need to be located mid-way between them.

[noanalyst]

Ok. I get it now. Will order the flora sensors today. Thanks for your help.

[noanalyst]

Hi again, I looked into the magnifying lens but it seems like it will be quite expensive cause I need one with a very short focal length (5 - 10 mm).

So what I want to do is place a shroud. Can you tell me where the shroud would go. I have attached a picture of where I plan to construct one. Am I correct? In my case I want to restrict the area to be detected by the sensor to an area of 5mm x 5mm.

Flora shroud.jpg (370.8 KiB) Viewed 388 times

[adafruit_support_bill]

That is correct. You need to surround both the sensor (center component) and the LED (yellow component to the left). The inside surface of the shroud should be black and ideally would taper to about 5mmx5mm - centered between the sensor and the LED.

[noanalyst]

Ok. Will try that. Thanks.

[noanalyst]

In regards to using a shroud, you mentioned it should taper to an area between the LED and sensor. Wouldn't it be more accurate right over the sensor itself?