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Hot!Ultra smooth led dimming

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NirVM
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2020/01/16 00:29:34 (permalink)
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Ultra smooth led dimming

Hi all,
 
I read in a few places about the possibly to use both the PWM and the DSM to achieve ultra smooth led dimming.
 
Has anyone implemented this and can share some info?
 
Thanks grin: grin
 
Nir.
 
#1

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    Mysil
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    Re: Ultra smooth led dimming 2020/01/16 05:37:12 (permalink)
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    Hi,
    What is DSM?
     
    There is an article in Eletimes
    https://www.eletimes.com/led-dimming-engine-8-bit-mcu-based-solution-switched-mode-dimmable-led-driver
    where a Microchip engineer describe some tricky LED driving using 16 bit PWM
    using current feedback.
    It is using PIC16F1779
    This is a chip with a lot of core independent peripherals, 4 each of most,
    so is able to control 4 strings of LEDs independently.
    In Microchip webpage for the microcontroller:
    https://www.microchip.com/wwwproducts/en/PIC16F1779
    look down in 'Documents' tab. In addition to Datasheet, there are links to a number of Application Notes,
    some about LED lighting and control, and some with example code.
     
        Mysil
    #2
    pcbbc
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    Re: Ultra smooth led dimming 2020/01/16 06:35:04 (permalink)
    +1 (1)
    DSM - Digital Signal Modulation
     
    OP seems to be referring to this MC product blurb page:
    "Microchip"You can also pair the DSM with 16-bit Pulse-Width Modulation (PWM) module in LED applications to create an ultra-smooth dimming engine and reduce heat to extend LED life.

     
    A tio to the OP: When you say "I read in a few places" always best to give references so others know what you are taking about.  Don't assume we've read or can find the same sources.
     
    Also do you have some specific design goal in mind, or are you just playing?
    post edited by pcbbc - 2020/01/16 06:36:15
    #3
    NirVM
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    Re: Ultra smooth led dimming 2020/01/16 22:39:29 (permalink)
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    Yes, this is the article I originally read before posting this. The problem is that it does not give any code and also, seems a bit too complex. Yes, this is a for a real life project for a customer but before I start designing I wanted to see if there is a proven solution to smooth led dimming. The project includes a 20 by 20 matrix of leds.
     
     
    #4
    pcbbc
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    Re: Ultra smooth led dimming 2020/01/17 02:06:31 (permalink)
    +1 (1)
    before I start designing

    Then you don’t know if there is a problem with dimming yet.
     
    20 by 20 matrix of leds

    You’re not going to find a PIC with 400 PWM and/or DSM outputs so this feature isn’t going to help you anyway.
     
    Are you dimming the whole array all in unison (but with some on and some off it a specific pattern) or wanting to dim each LED individually and separately?
     
    Depending what you define as “ultra smooth led dimming” you may be approaching FPGA territory to be able to control 400 LEDs and achieve granular individual brightness control of each.
     
    How are you going to matrix the LEDs? A standard 20x20 matrix requires 40 pins if done traditionally (of course there are solutions, external shift registers/decoders, Charlie pixel, etc). So you have problems there with a low end PIC device before you even worry about other things.
    #5
    concertinaman
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    Re: Ultra smooth led dimming 2020/01/17 02:52:31 (permalink)
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    If you want to control leds individually you may be better off with serial pixel leds such as the WS2812B's.
     
    The largest matrix I've done is 24x35 leds (840 leds). That used 59 processor pins, and you can't drive them directly because a led is only on for 1/24th of the time you get no brightness with the limited current available from a port pin. So 59 transistor drive circuits as well. With a matrix like that it's on or off only for each led. 
     
    #6
    ric
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    Re: Ultra smooth led dimming 2020/01/17 03:08:51 (permalink)
    +1 (1)
    concertinaman
    ...
    With a matrix like that it's on or off only for each led.

    It's fairly straightforward to control the brightness, (so all the lit LEDs are the same brightness) just by varying the width of the drive pulses.
     

    I also post at: PicForum
    Links to useful PIC information: http://picforum.ric323.co...opic.php?f=59&t=15
    NEW USERS: Posting images, links and code - workaround for restrictions.
    To get a useful answer, always state which PIC you are using!
    #7
    NKurzman
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    Re: Ultra smooth led dimming 2020/01/17 08:14:03 (permalink)
    +1 (1)
    TI makes dimable driver ICs that could also be used.
    #8
    KTrenholm
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    Re: Ultra smooth led dimming 2020/01/17 10:23:40 (permalink)
    +2 (2)
    Linear Tech (which I guess is Analog Devices now) also has some nice PWM controlled LED Driver ICs
    #9
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