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Topic: What type of led driver can be used to control a common Cathode RGB LED matrix (Read 964 times) previous topic - next topic

mfran89

Hey guys,

I am fairly new to using the RGB LED matrix and I am stuck trying to understand what type of LED drivers can be used to control this specific RGB LED matrix https://www.sparkfun.com/products/683. My end goal here is to create my own common cathode led matrix controlled by small prototype PCB board, so the smaller the chip is , and/or the less number of chips needed the better.

What I currently have is arduino UNO board running with atmega328P to program the LED matrix with.

Any advice would be greatly appreciated. 

-mfran89

johnwasser

Assuming the individual LEDs take 20 mA you will need a driver capable of sinking 20*n*3 mA where 'n' is the number of anodes per cathode.  A transistor per cathode should do the trick.  For the anodes you just need current limiting resistors.

How big a matrix are you making?
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CrossRoads

I don't think that's the right hardware solution.
What you need is 3 MAX7219. Each will have its Segment drivers connected to one color of anodes.
Each will need diodes between its digit drivers and the common cathodes.
Diode Anodes will connect to the matrix pins in parallel, and the cathode to the Digit pins.
This will take advantage of the MAX7219 shutdown mode:

"When the MAX7219 is in shutdown mode, the scan oscillator is halted, all segment current sources are pulled to
ground, and all digit drivers are pulled to V+, thereby blanking the display. "

Then write a sketch that alternately takes each one out of shutdown mode 1/3 of the time.
Control the 7219s with SPI, giving each its own slave select line for easier software creation.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

mfran89

Thanks guys for the feed back!

I am familiar with those MAX7219 , and I was wondering was there one led driver that could power an 8x8 RGB led matrix, or is my only option getting multiple MAX7219's?

The thing is I am trying to eventually create a LED RGB matrix thats 16x16 , so how many MAX7219's would I need for that? I mean instead of creating one 16x16 RGB Led matrix, would it be more efficient to daisy chain 4 '8x8' RGB led matrixs? IF so then there is no way I can create a small enough prototype board  that would fit all those MAX7219's on it so that's my conundrum.


CrossRoads

Sure you could.
Would look something like this , a just a little wider to accomodate 3x MAX7219 at each corner instead of just 1, and the diodes I mentioned, and with 8 more pins on each display.
Otherwise, you'd need like a 40-pin chip for each matrix (8 red anodes, 8 blue anodes, 8 green anodes, 8 cathodes = 32, + Vcc, Gnd, current set pin, serial data in, serial data out, clock, chip select, and 1 left over for something yet to be defined).
I suppose you could program a '1284P to do that, but you'd need current limit resistors.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

CrossRoads

http://www.ebay.com/itm/LED-Drive-Control-Card-For-RGB-Full-Color-Display-Sign-/190502735358?ssPageName=STRK:MESE:IT
http://www.ebay.com/itm/10x-PH4-RGB-Full-Color-LED-Module-Board-32-32-Dot-Matrix-For-Video-Wall-/310381738773?pt=LH_DefaultDomain_0&hash=item4844317b15

Here's another option - 32x32 RGB LED matrix controller. Mere $185.
Looks to use 8 shift register

12 $1.25 chips and some diodes not sounding too bad now!
http://www.taydaelectronics.com/catalogsearch/result/?q=max7219
http://www.taydaelectronics.com/1n5818-diode-schottky-1a-30v.html

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

CrossRoads

http://www.hobbyking.com/hobbyking/store/__26845__Colorduino_V2_0_RGB_LED_Matrix_Driver.html

Another option, a dedicated driver board, for common Anode parts.
http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=26938

Leave the page open for a while, one time offer price will show up, dropping the price  by nearly $1.50
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

fungus


Hey guys,

I am fairly new to using the RGB LED matrix and I am stuck trying to understand what type of LED drivers can be used to control this specific RGB LED matrix https://www.sparkfun.com/products/683. My end goal here is to create my own common cathode led matrix controlled by small prototype PCB board, so the smaller the chip is , and/or the less number of chips needed the better.


Why common cathode?

Common anode is sooooo much easier to drive using standard chips, eg. two TLC5940s will drive a common anode RGB LED matrix.


No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

mfran89

Ok that only reason I havent used the common annode version is because I keep reading on random forums that the common cathode matrix will last longer and the color variation comes out much better in comparison.

@CrossRoads Thanks for the schematic and links btw these are really helpful, and I am curious to what you about common cathode vs common anode is there a difference (aside from how to control it)

CrossRoads

Haven't researched any longevity or viewability differences. Have only looked at control differences.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

fungus


Ok that only reason I havent used the common annode version is because I keep reading on random forums that the common cathode matrix will last longer and the color variation comes out much better in comparison.


That makes no sense at all. The LEDs inside the matrix will be exactly the same, the only difference is the way they're connected.

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

Grumpy_Mike

Quote
Ok that only reason I havent used the common annode version is because I keep reading on random forums that the common cathode matrix will last longer and the color variation comes out much better in comparison.

Yes that sounds utter rubbish to me also. There is no reason why bonding a chip out differently would affect anything.

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