On 04/12/16 20:04, Dave Liquorice wrote:
On Sat, 3 Dec 2016 11:03:04 +0000, Tim Watts wrote:

How can it be so cheap?

It's China, I've got my eye on a 5 m 240 pixel IP65 strip on Amazon
for £23.00...

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

I just want something does a bit more than flash/fade simple
sequences. I suspect it won't pass management approval what ever I
do. I'd like it to do the simple "ordinary" things but also do
something to make people notice and think "Hey! That's different".

A Pi can drive one such data line directly using one of the DMA
controlled pulse shaping IO pins

There is one hardware PWM GPIO on a Pi but there is also libs that
provide software PWM on any GPIO. My three channels uses the hardware
PWM GPIO and two software ones. Each channel has it's own thread in
my Python program so they operate completely independantly. Each
thread also has a queue so you can adjust the fade up time, on time,
fade down time, off time and the LED level for "on" and "off", all on
the fly. Each thread then just loops round repeating that pattern.

- but you usually need a level shifter to gi from 5V to 12V for the
lamps.

5 V strips seem very common but you still need to level shift from
the 3.3 V of the Pi GPIO.

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.

Might be able to run more than one string from a Pi, it would depend
on the Pi being able to run at 800 kHz software PWM, TBH I don't
think it will or only for only a couple of channels.

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.

A full brightness strip showing white takes a fair bit of juice. Each
pixel draws around 60 mA (18.5 mA/LED), 240 pixels is as near as damn
it 15 A! Depending on the display patterns a car battery might not
last very long. And car batteries don't like being deep discharged
either.


24V makes a lot of sense with long LED strings, but I don't think anyone
has done a version of these addressable LEDs...