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Topic: Noob question about multiplexing and my weired project (Read 424 times) previous topic - next topic

LittleJ

Hy, first of all please excuse my poor english.

Second of all i am really new to arduino and programing (i mean i do this only as a hobby), but i'm doing my best reading as much as i can in my spare time.

Well i attach a picture of my sketch in google sketchup so i hope you can understand it better and aid me into my questions better.
(the small gray area should be led's and the red is utp cat5 wire )

So what i want to do, i want to add lights to my yard sidewalk since i am in the middle of adding sprinklers to my green zones i thought i could add some led's. Since i have some CAT5 cable lying around i thought i could use it to multiplex the led's so i can control them with arduino individually.

I am in the middle of documenting the multiplexing thing and i'm trying to understand it as better as i can (if anyone has any easy to understand multiplexing links i will appreciate it), i already managed to light up 16 led's multiplexed on a cat5 cable but all from 8 pin of arduino and a short cable 3m long, what i'm trying to do is add 3 shift registers a friend of mine had laying around 74HC595 one's. Can i use this type of shift register to control maybe lets say 48 led's , 16 led's on 3 separate cat5 wires? will it work fast enough from a atmega 328@ 16mhz ? (to multiplex all the led's so all will light up and pretty bright also)

I attach a .xls file how i will connect each led on a cat5 cable (please bare with me since i'm really new to electronics and led's and stuff like that), and since wire length is different from first led to last with maybe lets say 8-9 meters i suspect the brightness of the led will be different right ? will it help if i will use different resistors ? also can i power all this from arduino 1pwm pin for each shift register? 

One more question can anyone point me in the right direction with arduino programming to use the shift registers to multiplex led's ?

Thanks again and please excuse me if i post it in the wrong section and if i was not explicit enough.

fungus


I attach a .xls file how i will connect each led on a cat5 cable (please bare with me since i'm really new to electronics and led's and stuff like that), and since wire length is different from first led to last with maybe lets say 8-9 meters i suspect the brightness of the led will be different right ? will it help if i will use different resistors ?


Using resistors with LEDs is a poor way to regulate them. LEDs should be regulated by current, not voltage.

Chips like the TLC5916 or TLC5925 will regulate current so you don't need any resistors and cable length, etc. simply aren't an issue.

If you want PWM control of the LED brightness you can use a chip like the TLC5940.


also can i power all this from arduino 1pwm pin for each shift register? 


No. The amount of current (amps) provided by Arduino pins is very limited (only about 30mA).
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

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