More questions on color reader...

Lab has controlled background ambient? Real world does not.

PIC in an analog circuit :-) ...Jim Thompson

As Jim hinted you might have background light get in. Since there is only one phototransistor and not three with suitable filters the unit can't predetermined the ambient light energies per band. At night you may also see errors due to mercury vapor street lighting and so on, worst case also some PWM modulated stuff.

This will be worse with darker colors because the signal to noise ratio is lower.

BTW, "rainbow" can mean something entirely different in places like San Francisco :-)

Why is VCC connected to both power pins of U2?

The + input of U2C has no DC path.

What's going on with U8/U9/U10, especially U10?

John

It IS a PIc in an analog circuit! ;-)

Charlie

With nice linear phototransistors you could modulate the LED, and subtract out the "dark" current. That'd make it more robust to ambient light.

You mean like

"Red, Orange, Yellow, Green, Blue-Green, Blue, Purple, Pink" "Plus: Whitey, African-American, Gray Davis, Jerry Brown, ..."

Hi John, The upper pin is connected to ground. The VCC is on top of the bypass cap for the chip...

U2C hasn't given me any problems, to this point. ;-)

U8/U9/U10 are all complementary MOSFET pairs, doing the switching of the LED power to the LEDs.

A note on background leakage. The LED and PT are both oriented to the front of the case. I have black felt glued to the top and bottom of the case (about 1" wide) to block reflections and reduce ambient. My typical 'CLEAR' reading (no LEDs active) is in the

On a sunny day (Mon, 26 Apr 2010 15:07:02 -0700) it happened Charlie E. wrote in :

Did you ever hold that white plastic case against the sun and see how much light comes through? LOL

No, that sort of stuff (this one from back east):

I think Charlie does modulate the LED already. But no matter how linear the phototransistor, there comes point where it can't cope with ambient. Especially if things are modulated.

Sunlight and thus outdoor ambient has a lot of IR content which goes through just about anything. Indoors there will be very little, AFAIK CF lamps emit very little in IR percentage and windows keep it out as well.

You might need some foil in there as well, between plastic and felt.

Maybe a possibiliity, but the phototransistor is an ambient light detector, which has built in filters in the IR range to help shape the response curve. Pam was more concerned with possible UV contamination from the bright flourescents in the stores.

Charlie

Well, it just says "photo npn" in your schematic. Which one is it? IR filtered doesn't necessarily mean is has to be a very good filter.

It is a TEPT5600, a 5mm through hole part, which I bend to a 90 degree angle to face the front. The LED is a Kingsbright WP154A4SUREPBGVGAW RGB LED which I also bend to a 90. I have the LED at a 45 degree angle to the face plate, and the PT and LED are on opposite sides of the board, to reduce direct reflections between them.

Charlie

px

Hey Charlie, Can't help with your circuit, but it looks like a pretty cool device. It's the sort of thing that someone probably would never think of unless they were familiar with blindness.? I wonder if it could have application in teaching kids their colors, or for use with colorblind individual. Maybe an advanced unit to detect world currencies...??

My only thought is that maybe light is bouncing around in weird ways on the input. Try setting up some lights on your bench and see if you can emulate. Use different types of lights (flourescent, tungsten, basically, every wavelength you can think of). I would also experiment with different daylight times (outdoors, of course), as the Sunlight temperture varies considerably dusk to dawn. (You probably already know all this, right??!) Disclaimer: Amateur photographer here.

I notice you're in the United States. I thought I should point out a potential regulatory concern that involves offering products for sale before they have either been FCC- certified, or before the manufacturer (you!) has filed a Declaration of Confirmity. Honestly, I'm not sure which one your product would involve. Probably a DoC, but I don't know if they consider the LED emissions to require certification...?? Maybe someone here will know. Your PIC certainly operates fast enough to qualify for testing. I recall anything over 9kHz requires testing, though I could be wrong about that lower bound.

I think the FCC might interpret your website as advertising of the product, particularly in light of your web text suggesting wholesale pricing. (I realize the product is not ready for sale, but that's not really the point.) If the FCC were to draw that conclusion, it could subject you to an Official Citation or Notice of Apparent Liability. The former is a slap on the wrist involving no out-of-poekct money. The latter can lead to possible fines and in-rem forfeiture - (though all of these outcomes are highly unlikely).

Either way, a quick review of the Rule may put your mind at ease. The Rule is FCC 2.803 For convenience, here's the link:

Not knowing your situation, my recommendation is to be safe just add the following text to your web site (the page that has pricing info):

This device has not been authorized as required by the rules of the Federal Communications Commission. This device is not, and may not be, offered for sale or lease, or sold or leased, until authorization is obtained.

The above is the exact language specified by 47CFR2.803(c).

Enjoy!! And best of luck with the project/product.

-mpm

Are you saying that SF doesn't do rainbows?

Oh. OK.

It's probably banging up against its own ESD diodes in one direction or another. C10 makes the power amp ignore the offset. You could remove C4.

Why the 100r and 0r resistors S-G on the Pfets? That wastes a lot of Vled current... especially the 0r one.

Are you "auto-zeroing" out the background light? Are you checking for sensor saturation?

John

Figure 7 hints that this photodiode still lets in a ton of the near-IR spectrum:

Might also be good to put a snippet of metal tubing around it as a shroud because it seems to be a plastic diode. The more you can reduce the acceptance angle the better.

Lots of places do rainbows... there are various samples here:

That phallic-looking one in Boystown, Chicago seems quite fitting. :-)