Fence Post Lights - NeoPixels

[rathole]

Hi All, I am using breadboard RGB neo pixels to create fence light post lights. I have 400’ of cedar fence with post spaced 8’ apart. I have the first light up and running and it works great. (neopixels and mini breadboard housed in old peanut butter jar – looks cool). A web page (soon android app) with color picker send signal via the following:

(http://www.internetofcoolthings.net/xxx ... lor:R:G:B-> php script -> Digi Cloud service -> ConnectPort (in my home) -> Xbee attached to Uno -> NeoPixels

So here is my dilemma…

From everything I’ve read I cannot repeat the signal over such long distances. I thought of putting an AtTiny at each post but they don’t have RX/TX and adding a transmitter and receiver at each post would up the cost and footprint. An ATMega at each light would not be too bad (about 2.50 each). Not even sure if this would solve the distance problem…

Any thoughts would be welcome. I’m a professional coder but electronics hacker…

ty Paul

[zener]

Can you link the info that states you cannot repeat over a long distance? I am not an expert on these, but although I think there would be issues with long strings, I'm not sure data integrity would be the worst one. Maybe. Some issues I would expect would be power over that distance, as well as generating and sending a 1400+ bit string. I would think you might need somewhat thick power wires, at least at the beginning of the string. Maybe 18GA? And you might need a capacitor at each pixel to keep the power smoothed out.

[rathole]

I'll look for it but I remember reading they should not be greater than 6" apart... I'm not worried about power as I'm adding a solar panel at every x panels as needed. My biggest concern is being able to send one signal to all pixels which will be 2 per post @ 8' apart over 400'... ty

[dhalbert]

The control signal is regenerated by each NeoPixel when it is passed on. The datasheet for WS2812's says "Any two point the distance more than 5m transmission signal without any increase circuit." [sic]. The SK6812 datasheet says "plastic forward strengthening technology, the transmission distance between two points over 10M" [sic again]. So 8 feet should not be a problem.

Read the Neopixel Uberguide for some more guidelines, such as a large inrush cap across the power terminals, a resistor between the microcontroller and the first pixel, and 0.1uF decoupling caps across each Neopixel.

[rathole]

thanks... I'll check the guide. Got 3 up now without problem. I'll just keep adding and testing.

[bigjosh]

I think putting an ATTINY in each grouping would work great. An ATTINY's can be less than $1 each and can directly drive a NeoPixle string, ATTINY's also do have some hardware serial support, but you can also use something like SoftSerial on any data pin.

To communicate between groupings you might be able to get away with simple 5 volt serial if the cable is good, the baud rate is low, and the runs are not too long, but this application really calls out for a current loop like RS485. With this setup, all the ATTINYS would live on a pair of data wires arranged in a loop.

You can buy current loop boards that connect directly to a data pin of an Arduino or ATTINY, and they are astonishingly cheap and easy to use...

http://amzn.to/2b6Or4g

You'd need to make a trivial protocol to run over the loop so the Arduino master could tell the ATTINY slaves what to display. You'd probably just want to hardiare the RS485 board connected to the Arduino to be transmit-only and the ATTINY boards to be receive only to save pins and make things simpler- this would only require a single TX pin on the Arduino and a single RX pin on each ATTINY. Wire it up and see the fastest data rate your wires and runs can support, but it will likely be much higher than you need.

[rathole]

Thanks Joe... I'll do some research and post a diagram when figure it all out. I hopeI only need the RS485 module on the Arduino end and the Soft serial will handle receiving the 485 signal at the ATTiny? Diagrams I looked up show the RS module for both Tx Rx. Might be too much to have the RS module at each light from a size footprint.

[rathole]

Hi Zener... Here is where I found that after 6" apart you may get signal corruption

https://www.adafruit.com/products/1
558

Each pixel draws as much as 60mA (all three RGB LEDs on for full brightness white). An Arduino can drive up to 500 pixels at 30 FPS (it will run out of RAM after that). Using ribbon cable you can string these up to 6" apart (after that, you might get power droops and data corruption)

[zener]

I will take a guess at what they are saying there. (your link needs to be fixed BTW...)

I think they are saying that if you string together all 25 in that pack, and you use ribbon cable (which is very small gauge, 26AWG I think typically), then based on the current consumption (25 x .06A total at the end of the string = 1.5A max), you will potentially drop enough voltage that the things will no longer work. Since you are supplying a much better power rail (I think) you would not have that issue. The product pages need to give very general guidelines to people who may not know a volt from an amp, so in that case shorter is better, but I think it was a simplified ROT kind of statement. I may be wrong of course :)