Rgb Led Pwm

[Andrew Cowan]

Hi all.

I've been playing with an axe090 experimenters kit, and I've rigged up a simple RGB LED control program.

A potentiometer can be set, then pressing one of three PTM switches, labeled R, G, and B, transfers the potentiometer reading (0-255) to either the red, green, or blue element.

This all runs off a 28X.

However, the problem:
The LED is not particually bright. I have removed the protective resistors, as the duty cycle is always low, but this does not help. Looking into the LED, you see the red element, a blue element and a green element. You do not see a combination of the three. The LED is not really bright enough to project onto a surface - when you do, you always get the same colour (a slightly reddish white).

I assume the problem is that the LED is not diffused enough (it it diffused), or just not bright enough. Maybe I will try with seperate red, blue andgreen LEDs projecting onto one spot - this may help.

Any ideas?

A

 

[Dippy]

Well, for a start, high Fs and low duties are going to look dim. That's life and Natural Philosophy.
For, seconds, we don't know what RGB LED you've bought?

Is it one of those cheap KingCrap types from Ebay? (I'm just kidding, I'm sure its a top quality device from a reputable supplier)
So, you'll have the Data Sheet, you know the Duty and so you can calc averaged light output?

.....and..... crystal ball switching to full power and starting to smoke..... we don't know how you've wired it up?

 

[Andrew Cowan]

Is it one of those cheap KingCrap types from Ebay?

Yes.

Datasheet? You gotta be joking. It's ebay!

Looking at the given specs, it says that it is incredibly dim. 30mcd for the red, 25mcd for the green, and 20mcd for the blue. That explains a lot. With a 60 degree beam angle, this works out at about 0.063 lumens total.

So, I take it I should try a different make? I'm tempted to try one of the 94 lumen 3W luxeon RGB LEDs from ebay.

A

 

[eclectic]

Andrew.

If you substitute three separate LED's (1xR, 1xG, 1XB),

what does it look like?

Then order an upmarket RGB.

e

 

[Dippy]

"Then order an upmarket RGB" -- tee hee, quite right!

Then I shall phone 'Ebay-holics not-so-anonymous' hotline for Andrew and many others on this Foum.

PS. I have now seen 3 suppliers who have stopped trading unbranded LEDs made you know where..... well, so they say!!

All these lumens and cds: remember that 30mcd is perfectly bright as an indicator but NOT so great as an illuminator. But you've probably discovered that by now.

And PLEEEEASSSSSEEEEE check Data Sheets for those juicy LEDs. You have to drive them quite hard to get brightness.

And, of course, if you paid the extra and bought them from Farnell with next-day delivery typically , and they turned out to be crap you could get a refund --- good luck with Ebay.

 

[Andrew Cowan]

Now I have one super bright red, two superbright greens (which aren't that bright), and a superbright blue.

The program works perfectly, although it is hard to focus the three LEDs onto one spot.

Andrew

 

[Dippy]

Oh, so you did buy some cheap and nasty things from Eay then??

Lesson learnt?

 

[Andrew Cowan]

http://cgi.ebay.co.uk/Prolight-3W-RGB-LED-Star-6-Leg-High-Flux-94-Lumens_W0QQitemZ270281702551QQcmdZViewItemQQptZUK_HomeGarden_Lighting_Lamps_Lighting_SM?hash=item270281702551&_trksid=p3286.c0.m14&_trkparms=72:1301|66:2|65:12|39:1|240:1318

But it has a datasheet! It therefore must be decent!

● Please do not drive at rated current more than 1 second without proper heat sink.

OK Dippy - I concede. I'll see if I can find enough stuff to go over farnells £20 minimum order value.

 

[Dippy]

I'm sure you can find enough to spend over £20. I do it regularly!
Just make a list of bits you'll need for the next 3 months... easy.

How about Rapid or Maplin?
I haven't checked.

They won't be as cheap as Ebay, but they tend not to be as 'cheap' as Ebay.

PS. Two of my five cheap Philips-branded CFLs given to me 2 months ago are now spluttering so it's not just Ebay that supplies rubbish.

Question: How am I saving the environment when extra diesel powered container freighters are being sent from China full of goods to replace the previous crap that has conked prematurely?

 

[westaust55]

But it has a datasheet! It therefore must be decent!

It does not have to come from Ebay to have no or incorrect datasheet.

I bought 64 not so cheap) RGB LED's and the Australian supplier forwarded a datasheet with a warning to still check the pinout.

Sure enough the actual LED and the datasheet did not match.

 

[Dippy]

Probably because your supplier bought them from Ebay and flogged them on to you
Was it a 'brand name' product?
If it had been you could have gone to the Manuf's website...

I wouldn't consider buying a 'new' device without prior reading of a Data Sheet.
And sorry, anonymous stuff from Ebay gets a giant thumb down from me, but that's just my personal opinion.

PS. Andrew was being ironic in his statement.

 

[westaust55]

Probably because your supplier bought them from Ebay and flogged them on to you
Was it a 'brand name' product?
If it had been you could have gone to the Manuf's website...

I wouldn't consider buying a 'new' device without prior reading of a Data Sheet.
And sorry, anonymous stuff from Ebay gets a giant thumb down from me, but that's just my personal opinion.

I received the datsheet in advance.

Sure they came from China - what doesn't these days.


The advise they may not match came later after the purchase / with delivery.

 

[Dippy]

"Sure they came from China - what doesn't these days."

- sure thing, but there are 'anonymous' no-name brands, funny-name brands and 'proper' brands that are sold by the Big Boys....

The Big Boys (yes, they charge more) usually assess products before inclusion in their catalogues. Therefore they have a higher probability of being good. I admit you can strike lucky with odd brands too.

 

[gengis]

I just got some from ebay that are pretty good.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=310084012590Item&viewitem=

6,000 minimum 8,000 maximum mcd at 20 milliamps in a super flux package (square, pins on .2" centers) 120 degree beam spread, 13.99 USD for 20. Item number: 310084012590

Blue has to be driven a tad harder than the green and red, blue is dropping more voltage than the others.

Emitting Colour: Manual Control Common Anode in RED/GREEN/BLUE
LENS Type:Water clear

• Luminous Intensity-MCD: Min: 6000mcd Max: 8000 mcd
• Reverse Voltage:5.0 V
• DC Forward Voltage:
  • RED: Typical: 2 V Max: 2.4V
  • GREEN: Typical: 3.4 V Max: 3.8V
  • BLUE: Typical: 3.4 V Max: 3.8V
• DC Forward Current:20mA
• Viewing Angle:120±60 degree