The color reader... again!

Thanks for the compliment! I was at 205# (clothed). ...Jim Thompson

I have a lot of solder wick, which I use a lot of, and I bought one of those little rubber bulb things, but by the time you get the bulb to the hole, it has already solidified... :-(

Charlie

Ok, I replace the worst unit with an LED out of my stock from when I was prototyping, and the unit calibrates normally. So, it looks like I just have a few that are super efficient... :-(

Of course, I have 12 bad boards, and seven extra LEDs!

Charlie

Cost of 1 LED

Yes, hindsight is always great on this. What was funny was that in my preliminary prototypes, I had made a mistake and specifiec 32mil thick boards instead of the standard 64mils. When I made those up, they worked fine. When I went to production, I 'corrected' this to 64mils, and found that the phototransistor I was going to use wouldn't fit! Of course, I had some smaller ones that I had tried, and those did fit. When I get more boards, I will make sure that there is copper pour around all the LEDs (2 layer board) to help reduce bleed through. They are very near the edge of the board, so I kept the pour back a bit from the edge...

I will also go with the matte black solder mask!

Charlie

I don't have any good photometric gear, but I am starting to wonder if maybe these LEDs might be a little different in wavelength, so they get measured differently by the ALS...

Charlie

The rubber-bulb thingies are terrible, get the spring-loaded suction plunger type...

The good ones have a Teflon tip which can touch the joint and/or iron without melting. ...Jim Thompson

That's the kind I have, except mine is orange. Works great.

Mine too, but I couldn't remember where I got it... I may have "liberated" it from GenRad when they abruptly shut down the Phoenix operations :-) ...Jim Thompson

From IR LEDs I remember somthing like +/-3%. Not sure about visible light LEDs but you could ask the manufacturer.

Spectrum shouldn't vary that much. Are they intensity-binned?

Units of the same type can vary by 3:1 or so, typically binned A..F during testing and each bin may be only +/- 25-30%, which is barely visible.

Best regards, Spehro Pefhany

I have sent an inquiry to my assembler to see if there was anything abour the source that might indicate any problems. The spec sheet I have indicates that it is pretty tight on the wavelength spec...

Charlie

Exactly! I know that the ALS have binning, so I was sure to get a single bin, but the LED spec sheet doesn't indicate any binning... :-(

Charlie

Something that REALLY helps is after removing the through hole part (heat leg(s) and pull out), refill the hole with fresh solder. Then use solder wick or sucker to clear out the hole. If you do with a dry hole the chances are good that the pad may overheat and lift off the board. Maybe pull a machine pin IC socket apart and use the pins to make a temporary test socket for comparison testing if needed.

• (1) use black solder mask, or better yet (2) FLAT black solder mask. Perhaps to guild the lily, FLAT black solder mask and thick cardboard covering with cardboard pre-painted with flat black on both sides; pre-punched where oles are needed (make holes as small as possible).

• Double check illumination levels all possible angles, then channel gain and then detector photo sensitivity.

I'd get it from somewhere reputable. You want one that actually works! (their solder wick is probably OK though)

The rubber bulb things are useless. You want one of the aluminium reverse spring loaded mini bicycle pump type with a fresh snug fit flexible heat proof soft silicon cone tip on the end. It will pull most of the solder off a joint in a single go once you master the technique.

These days there is a guard around the plunger movement so you cannot get whacked by the recoil. Solder wick is OK but needs a lot more heat applied to be really effective. The wick has to be hot enough...

Regards, Martin Brown

You probably want to make yourself a trusted reference unit that can be used to check the ones being made by latching onto their light output waveform with a known good calibrated sensor (and preferably with a way of getting the raw measurement out easily).

A quick and dirty test of LED wavelength by eye can be done using their first order spectrum reflection in a shovelware CD (next to a reference one). It should be enough to see if the reds are the same nominal wavelength.

Hibrightness ones tend to be around 630nm these days. Older red ones were 650nm all +/- 5/10 nm and some with wider tails. It isn't uncommon for the older generation of pastel green LEDs to contain red light!

Paradoxically because of stronger long wavelength response by the photosensor it could easily be the LEDs that look visibly dimmer to the human eye that measure overbright on your device. It might be worth seeing if you can restore good calibration by putting a resistor in parallel with the overbright LED rather than physical replacement. (or altering the series resistance but that requires desoldering)

It seems odd to me that you cannot get enough adjustment.

out of curiosity what drive waveforms are you using to the RGB LEDs? Graycode or simple square waves at f, 2f, 4f ?

Regards, Martin Brown

Martin - if I understand you correctly,are you saying that if two side by side LEDs with slightly differing wavelengths are viewed at an angle via the write surface of a CD you may be able to discern by eye the difference - diffraction grating? Neat!

A bit OT, there are some interesting LED tech articles / app notes here.

Reading this thread got me interested......