Author Topic: 25 moteinos in 20 square meters  (Read 905 times)

taprik

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25 moteinos in 20 square meters
« on: July 26, 2016, 03:06:52 AM »
Hy forum,

I'm new to this forum and first time also with rfm69 (I'm used to xbees).

I'm working on a project involving 25 rfm69 (on moteinos) in 20 saure meters.
Actually we want to animate 24 strips of leds in a fountain. There will be an "appreciable" distance beetween the led strips and the controller (teensy) placed 3 meters from the border of the fountain.
We have found a possible solution to deal with the long cable but I'd like to evaluate an other solution : to have every strip independant with a moteino able to drive the strip of neopixels. So in this solution we will have a moteino sending basic information ("light them all", light half of the strip", ...) and 24 moteinos receiving this commands in the fountain and driving its leds strips (everything IP68 of course). The 2m leds strip is in a 2 meter polyamide vertical tube. My main concern is about the RF interference. Does the presence of so many moteinos in such a small perimeter will change the quality of reception. Is there any recommandations about the placement of the antenna in the tube ?
and
is it possible ?

emjay

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Re: 25 moteinos in 20 square meters
« Reply #1 on: July 26, 2016, 05:51:33 AM »
@taprik,

With the Teensy as 'Master', you can control the transmission rate and sequence. If you turn off ACKs, that is the only local transmission going on, so RF interference should not be a problem provided you chose a "quiet" channel to operate in.
A simple protocol of not changing the last received command until you get a correct CRC packet, with repeats of last command in the allocated time slot will work around not using ACKs at the expense of occasional slight delays in response.

Felix

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Re: 25 moteinos in 20 square meters
« Reply #2 on: July 26, 2016, 08:21:57 AM »
Nice project, the range is not a problem. Like @emjay said, don't use ACKs, only repeats if necessary. Also antennas enclosed in plastic tubes should be fine, just not in metal.

TomWS

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Re: 25 moteinos in 20 square meters
« Reply #3 on: July 26, 2016, 08:51:51 AM »
Driving Neopixels from a Moteino can be a problem due to the tight timing tolerances on the Neopixel protocol.  If you search this forum and look for light weight WS2812 library, you'll find a reference to a library that appears to work, although I've only tested it on a strip that was about 7-9 LEDs long. 

Tom

taprik

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Re: 25 moteinos in 20 square meters
« Reply #4 on: August 03, 2016, 03:41:00 AM »
Thanks emjay, Felix, TomWS

Actually I've changed my mind and will try to use one teensy with a rfm69 and synchronized teensys and 5 m cable length.

Nevertheless I'm interested in a network of moteinos with rfm69. My main concern is about latency. With xbees I can't get a correct latency with more than 10 xbees. A correct latency is less than 50 ms.
I've read that it takes 10-15 ms to send a message that is 60 bytes (without ACK) but will it be the same with 20 or 25 rfm69 ?

By the way I've found a ressource about moteino and neopixels (and possible timing issues)
https://github.com/hooroo/moteino_build_lights