Now to address actual comments ..
raschemmel:
If I go with multiplexing. If I understand correctly, if I want to turn on ALL the LEDs, each row would only be truly on 1/3 of the time, so to compensate it gets pulsed with 3 times as much mA to compensate. So when all lights in one row are ON, it would be 25 leds x 60mA = 1500 mA = 1.5 A?
You're still not getting it. You CAN'T DO THIS with the TLC5940 because of the resistor on pin-20. The current limiting resistor I keep mentioning that you keep ignoring. How can you put 60 mA into a led connected to a TLC if the current is limited to 20mA?
READ UP ON THE TLC5940 before you start making plans. You're getting the cart before the horse.
THIS IS FROM THE TLC5940 LIBRARY:
The 2K resistor between TLC pin 20 and GND will let ~20mA through each
LED. To be precise, it's I = 39.06 / R (in ohms). This doesn't depend
on the LED driving voltage.
- (Optional): put a pull-up resistor (~10k) between +5V and BLANK so that
all the LEDs will turn off when the Arduino is reset.
Yes, I don't quiet understand it all well yet. I do understand that resistor in pin #20 is very important. I was under the impression that the resistor made sure no more than 20mA go out per channel at a time, but that I would still be responsible that the power supply supplied enough mA to turn on all the channels. 16 channels x 20 mA = 320 mA. If I am understanding correctly, if I want to turn on ALL 16 LEDs that might be connected to a TLC5940, I would need to make sure the TLC5940 is getting at least 320 mA, and the resistor on pin 20 would guarantee that no matter what each channel wouldn't get more mA. As for how would I send out 60mA? Well I figured it would be part of my math/setup. For regular use, they suggest a 2k resistor for a 20mA mas output, so figured I could control the overall amount of mA that get to the chip (ie 1500 mA) and then I could do the math for the resistor to use in pin #20 to allow for up to 60mA vs 20mA at a 2k resistor (Hey, for a newbie not a bad way to think correct?)
From your replies, it seems the current/power supplied by the arudino would be enough to cover my 30 RGBs. You obviously know much more about the subject than me, so by no means I am questioning your knowledge. I am trying to explain my train of thought so that other newbies can take advantage of the information I am discovering myself.
Would it be safe for me to assume that for my project, 25 to 30 RGBs the power/current available from the arduino itself would be plenty, but if I wanted to go much larger (ie 20 TLC5940s daisy chained) I would probably need a separate power source?
raschemmel:
I agree. IF you turn them all at once, yes it would draw 1.5A.
Do you have any code yet ?
Ok, so it seems 1000 mA is the same as 1 A.
So if I did go with 25 RGBs with 5 TLC5940s, and turn them all at the same time, it would draw 1.5 A. 1.5 amps doesnt say much to me really. Can the current supplied by arduino cover the 1.5 amps?
As for code, none yet. I've found one good source that uses TLC5940s but no multiplexing. I plan to integrate multiplexing on his code, and I am sure that when time comes to it, I will be asking for help.
Magician:
If I go with 25 RGBs with the 5 TLC5940s, if I turn them all on at the same time, would it be 25RGBs x 3 (num of LEDs) x 20mA = 1500 mA = 1.5 A?
Yes.
If I go with multiplexing. If I understand correctly, if I want to turn on ALL the LEDs, each row would only be truly on 1/3 of the time, so to compensate it gets pulsed with 3 times as much mA to compensate. So when all lights in one row are ON, it would be 25 leds x 60mA = 1500 mA = 1.5 A?
No. LED"s usually could not be overdriven more than 2x times.
And with low multiplexing ratio (3x is low, compare to 8x or in some cases to 16x) you most likely wouldn't be able to tell a difference in brightness if you don't overdrive at all. Visual perception is quite non-linear things/curve, so 0.5 A may be o'key.
Again, please don't take offense, but I read a detail post that says that it is a myth that multiplexing saves current/power. According to them, the myth is that since you power different sets/rows at different times, you end up needing/using less current. For example, you mentioned .5A should work, since I will only be powering up 1/3 of the LEDs at one time, but they reading stated that to compensate for "less time" you send more current, and they do mention that Max DC is different from pulse, and that pulse can be up to 10 times higher than DC.
Mind you, this is a DIY project for fun, so I don't need to run brightness at is optimal potential. I have a general understanding of the 30fps and the visual effect. It just seems I might be going a bit TOO much reading, and I might be confusing complex/optimal configurations with simple ones.
raschemmel:
Read my reply to your OTHER POST. You have not given us any code. You don't understand how the TLC5940 works. You don't need to calculate anything and you could run both off the arduino because the leds are not all going to be on at the same time.
If you use a separate power supply (+5Vdc) for the TLCs, you need a common ground with the arduino or it won't work. You can
forget about the math. You have a schematic. build it as you see it on the schematic. As I said several replies ago , there is only
ONE current limiting resistor for ALL the leds and that the one I told you about on pin 20. You don't need to calculate current because the leds won't be on all at the same time.
I do appreciate folks letting me know what "will work" for my project, but might not work for lager projects. If you could clarify a bit better, it would help me and future readers. You state I don't need to calculate anything, and for 30RGBs that might just be the case. If I do multiplex seems I would be using up to 500 mA if I turn on the whole row (all 30 LEDs, 10RGBs), and if I don't multiplex and turn on everything on at once (all 90Leds /30RGBs) I would use 1.5 A. From what you say, seems Arudino 5v supply would cover these two scenarios.
But what if my project was much larger? Would at some point I need to do some math? (Remember, I am not trying to question your knowledge, just asking questions other newbies might have).
My main goal is to complete the project (less the coding) during the 10 days my son will be here. I am willing to do as I am told (ie just use the arduino power source to light up all my LEDs), but would also like to learn while I am at it. (ie 30 RGBs can be handled by the arduino power supply, but X amount of LEDs would require a separate power source).
Also, being that I am a newbie, I have found it very difficult to find info on power sources (maybe I am not using the right key words). If I did end up with a "Large" project, that would require a separate power source and math, how would I do it? I am not looking for someone to type up answers just for me, keywords I can use to search, or links to write ups would be very helpful.
Someone mentioned that for me to use a different power source, I would need a common ground, otherwise arduino wouldn't work. If I google "common ground' I would get lots unrelated hits. How would I search to find more info on what you mentioned? I don;t know much about electronics, but I know if I get a regular DC lighbulb, and connect the negative side of one battery, and the positive side of another battery it wont light up. With that in mind, I assume "common ground" wouldn't be as simple as connecting the ground from the arduino to the TLC5940, and the 5v, positive wire, of a 2nd power supply to all the anodes.