I need some RGB Ideas

oracacle

Senior Member
I am currently printing a sabretooth skull on my 3D printer and think that it may look good nicely lit up in a delightful selection of colours.
I am currently thinking about some of those APA102 LEDs, but I need to go and have a read of the data on the forum.
I am open to suggestion, it would be ideal if the LEDs could be colour set by the end user - the skull is for a friend of mine and wont have access to re-programme colours into the picaxe.
Once the electronics are prototyped and made I will print a base for it all to go in.

Oh and there is a deadline of about a week, less if possible. Good job I'm not working for the next three weeks.

Thanks for any ideas
 

newplumber

Senior Member
Hi oracacle your deadline is very short ... maybe you can get APA102 leds same day..but where I live
we have radio shack and they keep 3 or 4 items that you'll never need in stock but thier favorite
saying is "BUT....we can order it for YOU!:) "
My ideas are horrible but is the skull transparent and the leds shine thru
or would they be surface mount?
I personally like when the leds do the wave affect ,flowing like dim to bright to dim in a string
but with rgb they could just change color in a wave
my 1.75 cents anyway
 

oracacle

Senior Member
APA102 are on the way, fingers crossed should be here Monday.
Coding is going to be the hard bit.

The skull is white, the base I think is going to be black with the LEDs poking through. The base will be printed but I cant design it until the LEDs arrive and have done some testing with them to see how they light things up.
 

hippy

Technical Support
Staff member
One thing I did note is that APA102 seemed quite bright even at minimum brightness so not sure how that would fit with what you are imagining. If your skull is simply to be mounted and akin to a large multi-coloured lightbulb or colour changing ornament it may work with them just mounted at the bottom with some sort of diffusion.

For programming by the user Sony IR is probably the easiest. One could fairly easily allow a sequence to be programmed in. You would probably want a piezo beeper to confirm entries. Maybe '00n' for how many steps, 'nrrggbb' for what each step is, '0nn' (010-099) for the period between steps. '000' to toggle between stepping or fading or as a prefix for options commands, or something like that ...

Code:
0 20        Fade to new step every 20 seconds
0 03        Will have a 3 step sequence
1 99 00 00  Step 1 : Full Red
2 00 99 00  Step 2 : Full Green
3 00 00 99  Step 3 : Full Blue
If you want individual LED colours at each step it would need to be more complicated than that.
 

oracacle

Senior Member
I am surprised that they are not dimmable. I wasn't planning on using a remote - this will add the clutter that they have with 2 little boys running around causing the chaos the little boys tend to generate. The plan is some button on the back, I haven't decided on which PICAXE to use as yet, I know I have a 20X2 here but seems like over kill. But with that said, with these being programmable I could put user input on the hardware interrupt and have it sleep until user input to try save a little on batteries (I will give the option to be powered by wall as well. - I m not sure its worth it for the amount of power the picaxe is going to use will be tiny.
I have white plastic filament here which I could print a diffuser from.


Premelec that's an awesome site, that can give some start values. maybe some pre-programmed settings as well.

I have to remove some support material and will try and get a pic of the skull up later.
 

premelec

Senior Member
Note they ARE dimmable both by using lower voltage and the extra bits BUT when using the dimming bits the flicker rate goes way down - about 400 Hz I think compared to 2KHz [it's been over a year since i was working with them so this may be incorrect memory]. And of course if you use lower values of the 255 number they do dim also...
 

Reloadron

Senior Member
About a year ago a friend decided to illuminate his motorcycle using a LED kit. Came out pretty nice when it was done. Out of curiosity I bought a string of 5050 LEDs from Amazon to play around with. I can't say how they would compare to what you have. I did find that playing around with code and using a few MOSFETs as drivers to handle the current that interesting effects can be had using PWM outputs of a micro-controller including several PICAXE examples I found online. My LED strip was common anode so I switched the cathodes using some FQP30N06L N Channel MOSFETs. Using fade in and fade out makes for some really nice effects with the possible color schemes. Anyway, when playing around with LEDs I like using PWM for dimming or what I call fade in and fade out. Here is one of several threads on the subject in this forum. Depending on your LEDs and the brilliance as well as diffusion you may want to give a PWM scheme some thought. You also want to consider the current draw for the LEDs so you can come up with a driver scheme.

Ron
 

oracacle

Senior Member
Just a quick question - is it possible to connect 2 strips of the same length in parallel? Has any one tried it
Just come up with a bit of an idea which would be easier to execute if this is the case. the idea is still possible if it not.
I will try it out when I cut the strip I have but I am a bit dubious about cutting it before the base is finished (pretty sure I have the number right but better safe than sorry)

The testing I have done so far has gotten a programme that works, with either a user choose-able colour, or fading between colours - which can also be used to select the colour - and the dimming is sorted by altering the last bit of the first byte to be sent in the pre-amble.
The code that technical posted a while ago set the basis of the code for this project.
 

hippy

Technical Support
Staff member
Just a quick question - is it possible to connect 2 strips of the same length in parallel? Has any one tried it
Haven't actually tried it but it should be possible; each LED strip would see exactly what the other sees. You could theoretically cut the strip down to single LED's and control them all the same from one output.

I would guess the hardest part would be physical connection and what the input loading would be on the output pin driving them. But I can't imagine that would be too much with two strips or just a few but there may be some limit at some point.

You might be able to determine that by measuring the voltage and current through the driving line into the strip, calculate its effective input resistance and scale that up. If one strip is R then two strips will be R/2. So long as the current is below 20mA you should be fine.

Edit: The datasheet I have says RIN (pull high ) @ 5V is 570K, so about 9mA, so two should be 18mA, which should be okay but above that and one might have problems. actually 9uA, so shouldn't be a problem. Thought that was rather a high figure!
 
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newplumber

Senior Member
is it possible to connect 2 strips of the same length in parallel? Has any one tried it
I have to my stairs both strips connected to the same pins and is working flawlessly but that is just white leds not RGB
I don't see why it would not work...but then again i don't see why it does work either :)
 

oracacle

Senior Member
Haven't actually tried it but it should be possible; each LED strip would see exactly what the other sees. You could theoretically cut the strip down to single LED's and control them all the same from one output.

I would guess the hardest part would be physical connection and what the input loading would be on the output pin driving them. But I can't imagine that would be too much with two strips or just a few but there may be some limit at some point.

You might be able to determine that by measuring the voltage and current through the driving line into the strip, calculate its effective input resistance and scale that up. If one strip is R then two strips will be R/2. So long as the current is below 20mA you should be fine.

Edit: The datasheet I have says RIN (pull high ) @ 5V is 570K, so about 9mA, so two should be 18mA, which should be okay but above that and one might have problems.
That's pretty close, I am reasonably sure that each strip will be 25-27 LEDs in length. The final thing will most likely be run off of 3 AA batteries as well which give more like 8mA using the 570k as a base number. 16mA total gives a little more head room.
 

Reloadron

Senior Member
Just a quick question - is it possible to connect 2 strips of the same length in parallel? Has any one tried it
Yes, no problem at all with that as long as you can source the needed current. I have done it numerous times. The strips can even be of unequal length.

Ron
 

fernando_g

Senior Member
Perhaps a small-value (~10 ohm) resistor in series with each strip, just to equalize the slight differences in Vf, which would increase as the string heats up.
 

hippy

Technical Support
Staff member
Edit: The datasheet I have says RIN (pull high ) @ 5V is 570K, so about 9mA, so two should be 18mA, which should be okay but above that and one might have problems.
That's pretty close
No; was a maths error which I corrected but on the previous page now ... 9uA, so should be no problem at all. Of course it might be higher but it's not something I would have expected.
 

Bill.b

Senior Member
I have connected two 60 apa102 RGB strips in parallel in one of my Christmas displays.

All worked OK

apa102test.jpg



Bill
 

newplumber

Senior Member
Hi Bill
Looking at your shematic it seems you need a longer chip like the 40X2 :) joking
I should learn to keep my mind shut but I do like your schematic and thanks for adding it
I guess when I see unused pins ..i'm thinking like what else can I jam in it but I understand
every project is different

@oracacle When I get more APA102's I am going to test just how many a person can add in parallel
using fernando's idea
 

hippy

Technical Support
Staff member
When I get more APA102's I am going to test just how many a person can add in parallel
Given the control signal current draw for a single LED strip is about 10uA, and the current will double as you double the number of strips being driven; you should be able to parallel up about 2,000 strips giving 20mA current draw.
 

newplumber

Senior Member
you should be able to parallel up about 2,000 strips giving 20mA current draw
Thanks hippy lol okay 2000? that would be one expensive/bright test
I was planning on up to 16 strips tho in parrallel with 30 leds in each strip
of course not at full brightness ... don't want the neighbors to think we have ufo friends
 
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