On 03/12/16 09:25, Andy Burns wrote:
Tim Watts wrote:

I just watched another of Matt Johnson's videos and it seems he buys the
"pixels" (individual light unit) ready made from a dude on Guanzhong via
Aliexpress.

Last year I added a PCB with 8 LED pixels to an aliexpress order, just
to see how easy they are to drive.

I found they were easy enough to drive from a USB-serial adapter
(admittedly a specialised one that can do sync as well as async) and
knocked up a little python program to run through a few effects, so I
bought a 200 pixel length of LED tape as part of another aliexpress
order ... now's probably the time to dig them out.


This is the supplier the bloke in the video used:

https://www.aliexpress.com/store/gro...506643321.html

How can it be so cheap?

Anyway - I feel some fun coming on next Xmas

Nothing like Matt's - probably just a tree in the garden, or the edges
of the front of the house of something.

I think those chips drive the same way as the Pi's Unicorn Hat (latter
uses the LEDs with the built in chip rather than the external one, but
given the basic drive is the same (the whole string is a giant D-shift
latch register with D-in and D-out on each lamp - I suspect the protocol
is the same.

A Pi can drive one such data line directly using one of the DMA
controlled pulse shaping IO pins - but you usually need a level shifter
to gi from 5V to 12V for the lamps.

So in theory, if you can devote one Pi to a string, the Unicorn Hat
library should do the job - I've played with that and it's dead easy.

In a way, it might make the setup easier to use 1 Pi per string - write
a super simple daemon that sits on Wifi and accepts various pattern
requests and plays them out to the string.

At that point, you could even run the string and Pi in a weatherproof
box off a car battery (obviously with a 5V regulator for the Pi). It
would make the temporary installation even easier that Matt's.