Author Topic: Good way to turn on LED chunks one by one  (Read 948 times)

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Offline koko0

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Good way to turn on LED chunks one by one
« on: September 30, 2016, 11:48:58 pm »
I had a small hackathon where i needed to light many LEDs (about 40-50) from a 5V 0.5A outlet, while keeping an ESP8266 working.
AFAIK the best way to do it is to divide them into chunks, and light the chunks one by one fast enough so it will look like they are all on (but dimmed a bit).
i wanted to do it with basic components (555, shift registers, MOSFETs and other things i had there), while using 1 pin of the ESP8266 (other one was for a servo).
i couldn't find a way at the time to do it, so i moved on to a chip with more output pins, but i feel bad for doing it.

can you help me think of some creative ways i could have done it?
I know it a bit broad question, but it will help me think of ways for doing it next time i will have similar problems :)
Thanks!
 

Online Ian.M

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Re: Good way to turn on LED chunks one by one
« Reply #1 on: October 01, 2016, 12:02:56 am »
Roman Black's Shift1 system could do it with two 74HC595 SIPO shift registers to control the rows and columns of a multiplexed  8x8 LED matrix.  You could afford up to 35mA per column  which gives you an average of over 4mA with 1:8 multiplexing, plenty for high efficiency LEDs.   
Sequence:  Shift out a byte for the LEDs to light in one row, followed immediately by a byte with only one bit active to select the correct row,  send the Latch pulse to update all the outputs then idle or do other stuff for N milliseconds and repeat for the next row &etc.
 
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Offline stj

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Re: Good way to turn on LED chunks one by one
« Reply #2 on: October 01, 2016, 12:09:15 am »
this is already done in some tv and laptop backlights.
go look at the stuff sold by Linear Technologies.
they have chips designed to drive several strings of led's complete with current regulation and even voltage booster circuits - if needed.
 

Offline koko0

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Re: Good way to turn on LED chunks one by one
« Reply #3 on: October 01, 2016, 12:38:08 am »
Ian.M -
Thanks! i will look into it more deeply later.
I hear the term high efficiency LEDs a lot, and as a ebay buyer everyone says that.
are all the new LEDs high efficiency?

stj -
That's really cool to know!
but i'm looking to learn about the more popular chips.
 


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