pixel strips for POV with 30-40 leds?

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iainduncan

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Hi folks, I first asked about this about a year ago here, but then we went and built the other half of the show first. Now back to making POV pixel poi. I'll order some teensy 3 chips, but am wondering if anyone has positive experiences doing POV with strips of pixels, and if so, which pixel strips and driver library did you use? Our initial test with adafruit neopixel strips were interesting. We could get a POV effect when driving only 8 pixels using the adafruit library, but as we add pixels, the update rate slowed down *exponentially*. So I'm not sure if that was the library we used, or the strips, or both. But any rate, it wasn't going to work unless I hacked 'em up to drive off five pins, and even then, no idea if that would work.

Any tips much appreciated!
iain
 
WS2811 (aka NeoPixel) LEDs always take 30 us. The data rate is fixed at 800 kHz and 24 bits, so the time per LED is always 30us.

The LPD8806 LED strips are the fastest type. They use SPI and they can accept a clock in the 4 to 8 MHz range, which is much faster.
 
Thanks Paul. Have you heard whether WS2801s are fast enough? I don't mind the expense so much as the building hassle, so am trying to find something that won't be too hard to attach on a stick with them close together.

Iain
 
iainduncan, I did a quick mockup for low density WS2801 POV some time ago using fastLED as the library. The results were good for colour transformation and speed. At the time I decided to go with LPD6803 because of the form factor and density options. The image below is the test strip, just something I picked up to test the chip speed for image update rate, and the other shows the brightness of the ws2801 (i seem to remember that this strip used the 5050led, so brightness is the same as with other chip drivers using 5050). I decided to go with other options at the time as there was going to be too much in the way of soldering as there was not decent pre made form factor available.

Also, the ws2811 (eleven) are not good for POV. They update too slowly giving a speckled effect.

ws2801.jpgIMG_5872_1.jpg
 
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mortonkopf said:
iainduncan, I did a quick mockup for low density WS2801 POV some time ago using fastLED as the library. The results were good for colour transformation and speed. At the time I decided to go with LPD6803 because of the form factor and density options. The image below is the test strip, just something I picked up to test the chip speed for image update rate, and the other shows the brightness of the ws2801 (i seem to remember that this strip used the 5050led, so brightness is the same as with other chip drivers using 5050). I decided to go with other options at the time as there was going to be too much in the way of soldering as there was not decent pre made form factor available.

Also, the ws2811 (eleven) are not good for POV. They update too slowly giving a speckled effect.

View attachment 2275View attachment 2276
Click to expand...

Did LPD6803 work out well? Can you tell me what you wound up going with if you don't mind sharing? I'm also trying to find something that will allow density. If anything, we'll choose soldering something to get it dense though obviously that's not preferable.

Thanks!
Iain
 
I put the POV poi together about two years ago now, and tech has probably moved on. I used 15mm LPD6803 from Bliptronic, not sure if you can even buy them now. They have the chip on the underside of the heatsink board, and were only 15bit colour (but that was more than enough really, as in performances there really isn't need for the millions of colours situation) But, this method made the poi a little heavy. It allowed me to get 34leds in just over 50cm. They have four lines, so it meant soldering eight points for each led. There was also an issue with build quality where some of the leds had the blue and green leds reversed, meaning that it was impossible to use them.

IMG_0145-150x150.jpgIMG_0150-150x150.jpgIMG_0918-150x150.jpg

I wrote up a bit about it here for others to use: http://orchardelica.com/wp/pixel-poi-and-lp6803-leds-with-teensy
 
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