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Topic: LED project guidance (Read 1 time) previous topic - next topic

Norfy

Good afternoon,

I'm a relative newcomer to the Arduino world, I've been following many of the tutorials and building small projects to (hopefully) achieve my main goal project. Programming I'm fine with at the moment, the physical circuit building I'm hitting snags with at the moment and struggling to find the answers I need.


My aim project:
- To run two 10x30 led matrix of 300 LED's which will run behind red diffusers.
- Using a 12-14v input source
- Switchable cycle pattern control (can be added later)
- The matrix will be mainly used to display column scanning including PWM but I would like to have individual LED control.


So far I have:
- Many white 20ma 3.4v 20000mcd 5v LED's
- Two TLC5940 chips
- And not a clue haha.




From my research I'm finiding that the TLC5940 can only handle 120ma per channel, I require 200ma so I'm not sure how to get round this?

I've just found out that it's likely I'll need to use a MAX7219 chip to feed the LED rows. Not sure how many LED I can feed per channel though?

I'm struggling to find any information that isn't RGB based, and I'm coming across circuits that are using transistors (next thing to look into I guess).



I'm just after a bit of advice on building this circuit, what components I should be looking at and any information that could help me along the way. Just pointers really as I'm getting lost looking at components I wont need.


So any help would be very much appreciated. Thank you :)

CrossRoads

300 LEDs, use 5 MAX7219 to control them. 5V power supply is needed, can get a  5V/4A supply for $6-7, example of one I have used on my projects:
http://www.mpja.com/5-Volt-DC-Plug-Power-Supply-4A-Regulated/productinfo/18520+PS/
Here is a Duemilanove controlling 4 of MAX7219 to drive 256 LEDs, one more would drive 320.
https://www.youtube.com/watch?v=hwYqgyMc5S4
Can have 15 levels of brightness with MAX7219 for all LEDs connected. Not sure how useful individual brightness is on a matrix display.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

CrossRoads

"two 10x30 led matrix of 300 LED's "
A '328P based board can control 10 individual MAX7219s to drive the 600 LEDs. You can use discrete chip selects as I did, or daisychain them.
You can get them for $3.09 here
http://www.taydaelectronics.com/catalogsearch/result/?q=max7219
Don't forget at 0.1uF and 10uF cap per part, along with a current setting resistor, 10K works pretty well.
I also offer a breakout board if you wanted to wire each LED individually. If so, I would suggest male pins on the board and then 30 guage wirewrap wire to the LED legs.  The board is designed for easy daisychaining.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Chagrin

What type of LED are you using for this? You mentioned 200ma per channel.

Norfy

#4
Feb 19, 2016, 07:45 pm Last Edit: Feb 19, 2016, 07:51 pm by Norfy
thank you for the help and input CrossRoads. And thank you for the offer of the breakout board, it may be something I consider later on if I get stuck.


Why would you use the MAX7219 over the TLC5940? As far as I can tell they both do the same job but the MAX can supply a LED whereas the TLC sinks it (I may be wrong here).


I have an Arduino UNO board to drive this project, shouldve really included that.


Presumably I would need to reduce the voltage down from 12-14v to the 5v required for the project. Pretty sure I can get a converter later on.



On a 10x30 I would need to use two MAX chips for the 30 length, and one MAX chip for the 10 height? Sound correct?




This is similar to what I'm hoping to achieve but my lamps are a different size and shape. https://www.youtube.com/watch?v=3OtbUlfLEag


Obviously size and space are fairly tight, and I will need to consider waterproofing at a later stage when I consider getting a pcb made up.




Well things are becoming clearer and I have a few more areas to research now :)



 
Chagrin, I'm using a 20000mcd 20ma 3.4v standard type LED. I read that the TLC could only handle 120ma of LED per channel. I believed that my 10 LED per channel would pull a total of 200ma (10x20ma), what I didnt consider is multiplexing haha.




PaulRB

Hi, I'm afraid to say you're way off the mark about max7219 and tlc5940.

Max7219 can drive 64 individual leds in an 8x8 matrix and dim them together to 16 levels. Tlc5940 can drive 16 channels of leds and dim each channel individually to 4,000 levels. But if you put multiple leds in each channel, they can't be individually controlled.

You really must decide if you need individual led control.

Paul

Chagrin

I read that the TLC could only handle 120ma of LED per channel. I believed that my 10 LED per channel would pull a total of 200ma (10x20ma), what I didnt consider is multiplexing haha.
10 LEDs in series, all lit up, would still only consume 20ma.

To expand on what PaulRB said, the TLC5940 has 16 channels that sink current (switch open a connection to GND). The MAX7219 has 8 channels that source current (switch open a connection to VCC) and 8 that sink current. In that respect the MAX7219 is designed to be used for matrixes but the TCL5940 is not.

You can still use the TLC5940 for a matrix but you'll need an additional transistor and resistor circuit for each output of the TLC5940 you want to source current.

Norfy

Ok great thanks, food for thought.

So in theory I can use a MAX7219 to source the matrix and two TLC5940 to sink it if I reduce the matrix to 8x30 which will allow one MAX7219 to source?


Ive ripped/modified/drawn a circuit that I believe should work, a little unsure on the transistors and resistors. Could someone cast an eye over it, tell me if I'm in the right direction or barking up the wrong tree haha.



PaulRB

Norfy, you don't seem to be any closer to understanding. You can't use either max7219 or tlc5940 like that, it just won't work. Please re-read the advice you have already been given and start over.

Remember, the tlc chips can only sink current, they cannot source it like your diagram shows. The max chips are not designed to work with tlc chips at all in any circuit.

Norfy

PaulRB, Apologies, its seems I have made an error and mixed the cathodes and anodes up on the diagram.


Does this revised diagram look any better or should I go and research some more?



Grumpy_Mike

#10
Feb 21, 2016, 10:14 pm Last Edit: Feb 21, 2016, 10:15 pm by Grumpy_Mike
What part of:-
Quote
The max chips are not designed to work with tlc chips at all in any circuit.
Are you having difficulty with?

The MAX7219 uses an internal free running oscillator to do its multiplexing. The tlc5940 needs feeding with clock pulses from the Arduino in order to operate. There is no way to synchronise the two.

Quote
should I go and research some more?
A lot more yes.

Norfy

Okay, thank you. Seems I am way off the mark here. Back to the drawing board.


Thank you very much for your input everyone and I apologise for my noobness haha

PaulRB

Why not just ask the question "how should i do it"? But be careful to explain what "it" is, i.e. what you and to be able do do with these matrices.

Did you realise that if you absolutely do need individual led control, it will either require a lot of circuitry/chips, or less circuitry and the use of multiplexing? Also, multiplexing normally reduces brightness, e.g. 1 in 10 multiplexing results in a display that is one tenth as bright. Fortunately, the eye does not have a linear response to brightness, so it would only look perhaps one quarter as bright.

Norfy

Why not just ask the question "how should i do it"? But be careful to explain what "it" is, i.e. what you and to be able do do with these matrices.

Did you realise that if you absolutely do need individual led control, it will either require a lot of circuitry/chips, or less circuitry and the use of multiplexing? Also, multiplexing normally reduces brightness, e.g. 1 in 10 multiplexing results in a display that is one tenth as bright. Fortunately, the eye does not have a linear response to brightness, so it would only look perhaps one quarter as bright.
Im after two 'modes', one where I am able to allow full brightness to at least 5x10 of the matrix when switched, the rest of the 10x30 matrix needs to be running the leds at 50% brightness constantly and switching to roughly 80% brightness with a switch input.
The other mode I would like to have column and row scanning with pwm control and individual led control for displaying images/wording. The output brightness is less important in this mode.


I can build the circuit to operate the first mode without the use of chips no problem. My issue is the 'dancing' mode because that is where the chips get involved and I'm not quite getting it at the moment, or understanding if this project can actually be achieved.


Would it be possible? and if so what sort of hardware should I be using or looking into. Im not looking for someone to do the hard work of designing the circuit, just looking for pointers :) 

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