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Topic: LED driver chip(s) discussion (Read 2 times) previous topic - next topic

fungus

#15
Oct 30, 2012, 10:59 am Last Edit: Oct 30, 2012, 11:04 am by fungus Reason: 1

You could use RGB leds but lack of individual channel PWM means you can only turn a channel on or off. This limits the useful range of RGB colours to 7 (8 if you include all off) unless you device some fast switching to sudo PMW by turning a channel on/off quickly.


Soft PWM would be very difficult on a MAX2719 because there's no way to sync to the internal multiplexor. You could detect voltage on the outputs but getting it glitch-free would be a big problem.

All I meant was you could connect up RGB LEDs, not that you could do full 24-bit color displays. There's plenty of signs out there which are just red/green. Why not have blue/cyan/magenta/yellow as well...?

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

JoeN



Quote from: fungus

I don't see any reason why you couldn't connect three MAX7219 source pins to a common anode LED (or three sink pins to a common cathode).

nb. I haven't tried it...



The way the MAX 7219 works is it selects one of the eight cathodes to sink the current and provides current to zero to eight of the anodes for the segments that need to be lit on the currently selected "device" (or row or column if you are using a matrix).  It cycles through this refresh cycle at 800Hz.  So it is not possible to use two or more of these on one matrix *at the same time* because they will not be synchronized correctly.


I meant three source pins from the same MAX 7219. With one MAX 7219 you should be able to do a 2x8 matrix of RGB LEDs.



Anything less than 8x8 it works well, in monochrome.  I use it on another project on some 5x8 matrices.
I have only come here seeking knowledge. Things they would not teach me of in college.

xl97

#17
Oct 30, 2012, 03:34 pm Last Edit: Oct 30, 2012, 03:37 pm by xl97 Reason: 1
ok.. lets discuss the communication format/protocol they all use..

When I messed with the MAX7221 a 'little' bit..

the LedControl lib (for MAX72xx chips) is pretty easy/nice.. but someone showed me some SPI code to work with it as well..
(passing in binary 10011000 to create the 'pattern' I want to have on the led matrix/segment..etc..

one of my future projects is to try and mimic these animation effects:
https://www.youtube.com/watch?v=I_KGca_g96U&noredirect=1

(they are using .net arduino (netduino) variant and a MAX chip I believe)..

(in the end I have questions about adding this type of functionality to my project as it basically is a nArduino & Waveshield.. which uses SPI /timers to play audio..etc)



anyways.. so I have a bit (tiny amount) of familiarity with workign with the MAX chip.. are there pre-made libraries for these other chips as well?  and since they didnt note as being SPI format.. how do you control the chip?   bring some pin hi/low.. write/edit some values..then bring the pin back hi/low so it 'upates' this data?

(sounds like SPI to my noob mind?)

thanks


JoeN

Only other one I know of is for the TLC5940

http://www.arduino.cc/playground/learning/TLC5940
I have only come here seeking knowledge. Things they would not teach me of in college.

xl97

nice...

probably works equally as well for the 5945 then too?  (from what "I" could see only difference was the total mA/current available?)

I updated first post with link to this.. as well as links to the libraries and datasheet for the MAX chips..

just so Im clear on 'terminology' here.. when people say 'ShiftRegister' these are the (type) of chips they are talking about..yes?
I see it used commonly.. (mostly with this chip: 74HC164)..  but others as well..




thanks

JoeN


nice...

probably works equally as well for the 5945 then too?  (from what "I" could see only difference was the total mA/current available?)

I updated first post with link to this.. as well as links to the libraries and datasheet for the MAX chips..

just so Im clear on 'terminology' here.. when people say 'ShiftRegister' these are the (type) of chips they are talking about..yes?
I see it used commonly.. (mostly with this chip: 74HC164)..  but others as well..

thanks


These are more speciality LED drivers that have a shift register as part of their internal architecture.  I would say the 164, 165, and 595 (and some others - 299, 395, etc.) are what people are talking about when they specifically talk about shift registers.
I have only come here seeking knowledge. Things they would not teach me of in college.

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