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Topic: MAX72xx RGB (Read 988 times) previous topic - next topic

coolnumber0129

im considering the MAX72xx to control my 16x6 RGB backlight for my keyboard
will 6 MAX7219 work?
if so, how do i make it work?
if not, what will do the trick?

thanks in advance

CrossRoads

You could make it work, using 3 for each 8x6 block, You'd have to do your own time multiplexing between colors, putting 2 in shutdown while the 3rd was active, and adding diodes to isolate the active part from the inactive parts.

Pretty sure there are better options.
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.

coolnumber0129

thanks for the reply!
although i dont understand 50% of it :P
i will research more and post it here if i find anything

CrossRoads

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. The MAX7221 is identical, except
the drivers are high-impedance.

So with MAX7219, you need diodes between segment (anode) drivers, and diodes between the digit (cathode) drivers. Then the part that is shutdown is not pulling the anodes of the active device low, and does not drive the cathodes high. 
MAX7221 is better, the outputs are just turned off, and do not interfere with the other devices.
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

I'd draw a picture, but it's late and I'm tired.
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.

coolnumber0129

woah....
thanks for the detailed explanation!
your willingness to help people is mind blowing
thanks again!

Zapro

Look at the TLC5940 instead.

// Per.

PaulRB

#7
Jan 16, 2016, 10:49 am Last Edit: Jan 16, 2016, 03:08 pm by PaulRB
Or ws2812b leds.

With max7219 you will get a choice of 6 colours. With ws2812B you can mix many colours and shades, and wire them in one long chain back to a single Arduino pin. No extra chips, because each led has its own built-in driver chip.

Paul__B

Actually, a MAX7219 can control basic RGB LEDs quite well - with the constraint that you do not have individual intensity control.  For keyboard lighting, this will be no concern as you only want basic colours.

Now unless you use six-wire RGB LEDs - that is, with both connections separate for each colour - you can only use two LEDs per row or column as you are using 6 of the 8 lines for the colours and the other two cannot partly power the RGB LED, so the MAX7219 can control just 16 RGB LEDs.  So it seems that six of them would be fine for your 6 x 16 array, each MAX7219 controlling an entirely separate array of 16 LEDs.

coolnumber0129

Or ws2812b leds.

With max7219 you will get a choice of 6 colours. With ws2812B you can mix many colours and shades, and wire them in one long chain back to a single Arduino pin. No extra chips, because each led has its own built-in driver chip.
that would actually be perfect!
i will research about it
thanks!
Actually, a MAX7219 can control basic RGB LEDs quite well - with the constraint that you do not have individual intensity control.  For keyboard lighting, this will be no concern as you only want basic colours.

Now unless you use six-wire RGB LEDs - that is, with both connections separate for each colour - you can only use two LEDs per row or column as you are using 6 of the 8 lines for the colours and the other two cannot partly power the RGB LED, so the MAX7219 can control just 16 RGB LEDs.  So it seems that six of them would be fine for your 6 x 16 array, each MAX7219 controlling an entirely separate array of 16 LEDs.

does the MAX7219 use PWM to control the colors?
if so, how do i use the PWM?

Paul__B

The MAX7219 uses PWM to control overall brightness.  Thus I said:

with the constraint that you do not have individual intensity control.  For keyboard lighting, this will be no concern as you only want basic colours.
Red, yellow, green, cyan, blue, magenta.

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