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Topic: CharliePlexing LED --Method to get more I/O's (Read 169 times) previous topic - next topic


Oct 05, 2015, 07:15 pm Last Edit: Oct 05, 2015, 07:15 pm by destiny2008

I am using 7 I/O for LED  + 4 Analog as output for LED chaser or knight rider or other, but i need more without having to add parts that would take a lot of m -amps ...

total 11 pins to drive LED , any better way Load wise and to get about 20 pins (LED) without adding more Ic chips (low current ones available?)

 ( Looking at load and consumption as it is running from a remote battery). ~CR20XX



LEDs are drawing power.
Are they all going to be on at the same time?
That would be pushing the package current limits
if each LED was at 20 ma and each lit.
You could run a matrix with some outputs driving
as pullups and some as pull downs.
3X4 could do 12 LEDs but multiplexed ( not all on at the same time.


Oct 05, 2015, 09:53 pm Last Edit: Oct 05, 2015, 09:53 pm by destiny2008
they will flash / fast blink and bounce , not light at the same time
only 4-6 out the 12-20 lit at the same time



so multiplexing ? and i can control them seperately?


Yes, so long as you can tolerate that some are really not on at the
exact same instance, they just look that way to the eye.
If you really need a solid continuous light out of each, that
is not multiplexing.


Oct 06, 2015, 12:06 am Last Edit: Oct 06, 2015, 12:22 am by destiny2008
the thing is i need to have like 5 blinker on each side including like 4 in the middle to act as brake pattern


right : 2 'X' + 5 '0' (head bounce)
left: 2 'X' + 5 '0' (head Bounce)
brake: all blink pattern ..

doable with muliplexer you think.

Actually on another tought , I could use pins 2-8 then the A0-A6 to get 14 right?

-the array of 14 led's draws current of 350 mA from the source. is that acceptable as a whole to the arduino?


I'm not sure what the ratings are and it depends on the package. I seem to recall
something on the order of 200 ma or just 10 LEDs on at any one time.
With 350ma, you are most likely pushing the limits of the chip for total current.
( do look it up on the AT's web page ).
Using 2-8 and a0 to A6 directly is 14 individual signal. No need to multiplex
but you could quickly reach the package limits.
You can so 20ma on any one pin you just can drive all the pins at that level
at the same time.

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