Christmas Star project

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I have no 0603 LEDs to try it out. Been using 1206 on similar projects and a 750 ohm resistor is brighter than I really want for this project.
Been contemplating on using an 0805 instead?
 
The package size doesn't dictate the brightness, and one "0805 LED" isn't the same as another.

Since you've talked about using a service to stuff the boards, if you want to know what it's going to look like then you need to use the LED that they're going to install. You at least want one with similar characteristics.

As I said a while back, I've had some blue leds that'll fry your eyes out they're so bright, while others are more reasonable.
Also, you might need different resistor values for the blue vs white leds to keep them about the same brightness.

Just trying to save you some grief since it'll be a pain to try and change the resistor arrays once they're installed.
 
I researched the data sheet and the blue LED - 70-150 MCD
the white is 200-330 MCD
Maybe alter the resistors but I want the white to be brighter but?
 
Looking at JLC's "basic" parts, blue and white LEDs are a mixed bag (there are no 1206 LEDs in the basic list).

The table below shows the 0603 and 0805 LED characteristics. The 0603 white LED is a real outlier compared to the rest. Look at the MCD values at 5mA. The others are reasonably similar. JLC does have a wide range of LEDs available on the extended list but I'm not crazy enough to categorize them all. The data sheets are available with a click.

Following the table are two graphs showing luminous intensity vs. current in different formats. Given the luminous intensity at 20mA, you can estimate the intensity at lower currents. For the Hubei KENTO Elec LEDs, I estimated that the intensity would be 1/3.75 less at 5mA than at 20mA. A point to note is that luminous intensity is falling rapidly below 5mA, and these LEDs (with a notable exception), aren't all the bright to begin with.






 
I wish this part had a number I am using 0805
a white BASIC part is C34499


LIGHT EMITTING DIODES (LED) BLUE 463~466NM 50~60MCD@20MA TOP VIEW 0805 ROHS Basic PartHUBEI KENTO ELEC225675
 
Yes, and??? You've absolutely missed every detail in my last post. Those are the two 0805 LEDs in my table. You're looking at the MCD @ 20mA. At 5mA, the luminosity will only be 13 – 16 MCD.

But according to version whatever of your schematic, you won't even be using 5mA. You've talked about 510 ohm or even 750 ohm resistors for 2 LEDs in parallel.

510 ohms results in 4mA shared between 2 LEDs – that gives you 2mA per LED, which will give you 5% of the brightness that 20mA would give you.

750 ohms results in 2.7mA shared between 2 LEDs – giving you 1.4mA per LED, which will yield about 1.5% of the brightness that 20mA provides.
 
yes I realize I need to change the resistor values but need to calculate.
Thinking towards 30-50% of brightness. back to the drawing board.
What bothers me is the white led has no part number so working off another led datasheet.
 
thanks it came up with part number C2290
after recalculating resistors I find 180 ohms to 220 ohms for 5 ma
thanks for the help.
 
Be perfectly clear. I am not recommending 5mA or any other current level is appropriate for what you're trying to do.

All I am suggesting is that less than 5mA will be essentially useless.
 
I understand your not recommending.
My worry is too small of a resistor and one led burns out then POW! MAYBE
 
What's the absolute maximum current the LEDs can handle? It's in the datasheet, and is likely 50mA. LEDs are pretty unspectacular when they fail with anything close to reasonable voltage and current levels.
 
If you ever do get a board ready to submit, in about the last step prior to committing your board to build, a picture like this will be shown. This is the last step between you and a costly mistake. Ignore the silkscreen which is not well-rendered at this point. Focus on the parts shown. If they aren't in the picture, they won't be on the boards you receive. Notice the upper circle and the empty footprint - no part. Sometime after I checked for sufficient stock, it went low on stock. Fortunately, there's a pin-for-pin compatible alternative, so this problem is easily remedied.

Now look at the bottom circle. The part is shown 90 degrees to the footprint. Would somebody have caught this error? Possibly. If somebody caught it, there's a 50/50 chance the chip would have been oriented correctly. But boards with the chip installed at 90 degrees would have made a good conversation piece. It's up to YOU to spot these problems. The $7 engineering fee at JLC doesn't provide much room for hand-holding.

 
thanks for the info.
Still sorting out the LEDs on the board but getting closer to being finished and ready for submission.
If after all is done and I have a working board what would be the best method to share with this forum? thinking all the gerber files?
 
The new and improved result. Changed the missing part to an available part and edited the Pick&Place file for the correct rotation of the IC at lower right.

 
part availability is worrying me.
trying to pick parts with lots in inventory. Thinking maybe the day I place order, check stock first and hopefully thet are in stock.
The pick n place machine hopefully will install parts that are at an angle?
 
almost done with routing traces, just need to do some house cleaning.
I changed my ICSP from through hole to SMD on the board bottom layer. Just used 2mm wide traces. I have surface mount 5 x 1 headers. Should work.
resisted the easy way out running traces between the resistor networks pads.
QUESTION? how to post a screen shot of board. Tried "prt scr" but?
 
"...just used 2mm wide traces...."

Unless you did something more than put down some tracks, you know those will be covered by soldermask, right?

Pressing [prt scrn] or sometimes [shift] [prt scrn] captures a screen shot into memory but nothing else.

You can paste it ([cntr] V) into a program like IrfanView, crop it to size and save it as a jpg.
 
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