0

DotStar Power Supply and Clock DAta Requirements
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

DotStar Power Supply and Clock DAta Requirements

by drdougcameron on Fri Feb 08, 2019 5:18 pm

Starting a project with DotStar LED strips. Will use a Raspberry Pi 3 Model B+, SATA HDD/SSD Storage Expansion Board, X820 V3.0, 100GB 2 1/2" hard drive, and a X820 V3.0 SSD&HDD SATA Storage Board Matching Metal Case/Enclosure. Using a 74HC125 as a level converter and driver for the clock and data lines. LED string will be 100 ft+ in length. Will be using LED strips with 30 RGB leds per meter.
My questions are as follows:
1. Will the 74HC125 be able to drive the clock and data lines to this length, or will I have to upgrade to a more powerful driver such as a Power MOSFET such as IRL B8721 PbF?
2. Can I successfully power the Raspberry Pi w/hard drive with the same power supply as used for driving the LED strips?
3. At approximately 30 meters per 100' of LED strips and approximately 9 amps per 1 meter strip, we're looking at a rather hefty power supply. The question being, should the 5 volt power supply be connected every meter (or so)?

Your response greatly appreciated ..

Doug Cameron

drdougcameron
 
Posts: 2
Joined: Thu Dec 13, 2018 8:47 pm

Re: DotStar Power Supply and Clock DAta Requirements

by franklin97355 on Fri Feb 08, 2019 6:38 pm

1. Will the 74HC125 be able to drive the clock and data lines to this length, or will I have to upgrade to a more powerful driver such as a Power MOSFET such as IRL B8721 PbF?
The Dotstars are in themselves repeaters so the signal will be repeated every pixel.
2. Can I successfully power the Raspberry Pi w/hard drive with the same power supply as used for driving the LED strips?
As long as the supply is stable you should be OK.
3. At approximately 30 meters per 100' of LED strips and approximately 9 amps per 1 meter strip, we're looking at a rather hefty power supply. The question being, should the 5 volt power supply be connected every meter (or so)?
With adequate gauge wire, you should be OK with a connection every couple of meters.

franklin97355
 
Posts: 20105
Joined: Mon Apr 21, 2008 2:33 pm
Location: Lacomb, OR.

Re: DotStar Power Supply and Clock DAta Requirements

by kevinjwalters on Fri Feb 08, 2019 7:26 pm

What's the physical layout of the pixels and what update rate are you attempting?

kevinjwalters
 
Posts: 221
Joined: Sun Oct 01, 2017 3:15 pm

Re: DotStar Power Supply and Clock DAta Requirements

by drdougcameron on Sun Feb 10, 2019 9:33 pm

Physical layout will be a single string. Update frequency has not been determined but would like it to be as quick as the pi will allow.

drdougcameron
 
Posts: 2
Joined: Thu Dec 13, 2018 8:47 pm

Re: DotStar Power Supply and Clock DAta Requirements

by kevinjwalters on Mon Feb 11, 2019 8:22 am

If you don't already have experience of this type of project I'd focus on two areas, safely handling and distributing the power and ensuring the update rates you want are feasible.

There are some useful cautionary tips for powering in Adafruit NeoPixel Uberguide: Powering NeoPixels (NeoPixels have different slower control "protocol" but power issues are the same). If you get this wrong then you'll either end up with dim/non-functinonal LEDs at one end or you'll start a fire, latter is not a good scenario. High currents demand good physical design, e.g. protection from dropping a spanner or loose screw to avoid the short/melt/fire. [Added later]: Another example from forums, smoke from LEDs: General Project help: led board caught fire.

For update rates, the professionals in this field often use multiple controllers when there are a huge number of pixels in displays. If you are at 30x30=900 pixels the upper limit of how fast you can update these based on the wire speed is 4 (RGBI) * 8 bits * (900 + 2) / 4 MHz (based on value in adafruit_dotstar.py (CircuitPython Library)) = 7.2 ms. That's actually pretty good. If you want fast updates you'll need to use C rather than CircuitPython and keep any other processing brief in the update loop. The default of 4MHz will only work on short cable lengths betweeen controller and DotStars. I should have known better but I tried taking mine from 15cm to 4m. It took a while to twig that this was only going to work at undesirable lower speeds, perhaps 100-500 kHz. In the end I extended the power with a chunky copper cable and colocated the Gemma M0 in the Christmas tree with DotStars.

You can prototype the code with a 1m run of pixels but with pixel count set to 900, the last pixel will just shift data into oblivion. That'll tell you quickly and cheapily whether your code does what you want at the rate you desire.

I didn't need/use a 74HC125 when I was using a (USB powered) Gemma M0 with its 3.3v logic outputs with a APA102C (DotStar) strip powered by 5v. What's the motivation for this?

[added later]: There's more power supply and distribution tips in 1500 NeoPixel LED Curtain with Raspberry Pi Fadecandy: Power Topology - I certainly agree with author on the comments on low/no-brand PSUs via eBay.
Last edited by kevinjwalters on Thu Feb 14, 2019 7:36 pm, edited 2 times in total.

kevinjwalters
 
Posts: 221
Joined: Sun Oct 01, 2017 3:15 pm

Re: DotStar Power Supply and Clock DAta Requirements

by kevinjwalters on Thu Feb 14, 2019 7:16 pm

I see use of a 74AHCT125 for DotStar, perhaps I was just relying on luck using 3.3v logic? Could also be related to use of a LiPo on Adafruit boards and the lower voltage they put out particularly near end of discharge.

kevinjwalters
 
Posts: 221
Joined: Sun Oct 01, 2017 3:15 pm

Re: DotStar Power Supply and Clock DAta Requirements

by AevaLighting on Fri Feb 15, 2019 9:47 pm

ws2812b sk6812 led strip are same procotol,

apa102c and sk9822 are same protocol, apa102C and sk9822 led are packed in China.

apa107 leds now preform better than apa102c and sk9822, more faster and stable.

Have buy few from aeva lighting to test,
apa107 are better than sk9822/apa102c, sk9822/apa102c are better than sk6812.

AevaLighting
 
Posts: 5
Joined: Fri Dec 28, 2018 12:27 am

Please be positive and constructive with your questions and comments.