Stair-lighting DMX controlled

[jakob]

Hi, i have a project for making a interactive stair-lighting kit. I want to have a LED strip on each step, and be able to control them independently. My first idea was to just use a Arduino and connect them up, but since my father is insisting on having RGB-strips, this gets a bit difficult. Because i would then need 42 pins on my controller (14*3=42). I thought about using some DMX dimmers, because its easy to make a DMX-controller, problem then is that i need wires worth around $80. So my last idea is tho make a bus, have small controller boards on each step. I made a quick schematic (attachment). The idea is to have a DMX bus and a power BUS. and use a Raspberry pi or something to send DMX-signals. Because i could easily make a app to control it.

Could anyone check my schematic and see if it should, function? Because then i would order parts, and try it. Also i have no idea how to draw it out in the board-view thingy in eagle. So if anyone would help me make a compact PCB design, please PM me!

I have not started to write any code for the ATMEGA yet. But i think it will be pretty straight forward. Because it is the chip that is in one of the arduinos i could burn the bootloader, and i believe there exists libraries for receiving (and sending) DMX512. then i would just make each chip hard-coded with 4 DMX adresses (R, G, B, DIM). but first i want the schematic and PCB to actually be functional. And price-optimal.

[firehopper]

what about using ws2812b led strips or neopixel strings?

[rob77]

what about using ws2812b led strips or neopixel strings?

+1 on led strips with integrated controllers - you can chain up all the leds to have one long bus but still able to control individual leds in the chain.

[jakob]

what about using ws2812b led strips or neopixel strings?

+1 on led strips with integrated controllers - you can chain up all the leds to have one long bus but still able to control individual leds in the chain.

I hadn't even thought about that That was a really good idea. I would have to connect the strips in series then? Wich means that i will have to drill two holes in each step?

[botcrusher]

you could wire them in series, or you can use your microcontroller to drive the strips on different pins.

FastLED is an excellent library. I use it with a chain of 300 WS1812b LEDs and it chews through it no problem.

[ajb]

A few comments on your schematic that should be instructive even if you scrap it in favor of another method:

- It's always a good idea to have pulldown resistors on the gates of your output transistors so that if your MCU fails to drive them (for instance during programming) they don't float into their linear region and cook themselves. 
- LED4 is not connected properly.
- Don't leave DE on the RS485 transceiver floating.  Some parts may be fine like that, but others may start driving the bus unintentionally.  You may as well wire up the TX line as well so that you have the option of transmitting.
- Don't forget to include a programming header, either UART for Arduino or a 2x3 AVR ISP header.  Pulling the chip to reprogram it is a PITA.
- Don't connect activity LEDs directly to the DMX signal lines.  It loads the bus unnecessarily, and isn't a very useful indicator--it only shows you that there is some sort of signal present on the bus, but won't tell you if the data is valid or even if the wiring polarity is correct.  Also, RS485 is designed to tolerate a wide common mode range, which won't play well with that LED to ground.  Better to have an LED driven by your firmware that can indicate that valid data is being received.  If you really want a simple 'bus activity' indicator, connect it to the RO line of the transceiver.

[jakob]

Thank you for replies. I think the idea of using ws2812b led strips is really good. The only thing i am wondering about here is power usage. It seems that 5 meter uses 9 ampere  . Which brings me close to 27 Amps . Could anyone please confirm that? Also how thick would the power wires need to be?

BTW: Thank you ajb for the corrections! 

[botcrusher]

Meh.
Many cheap old ATX supplies can comfortably have 30A drawn from the 5V line. Run the strips parallel on different 5v wires and you'll be fine.

[jakob]

Thank you guys for all the help!  O0

Meh.
Many cheap old ATX supplies can comfortably have 30A drawn from the 5V line. Run the strips parallel on different 5v wires and you'll be fine.

The power supply is not that big of a problem, but if i get you right you say that i should run two power wires (+ and -) to each strip. This would result in me needing about 60 meters of power wire for my seven meter staircase. So i feel like there have to exist a beter solution for this. I have also calculated all this over again. I looks like i am getting closer to 50, amps.

One meter of the LED-strip has 60 LEDs. Each LED draws at max 60mA? Which means one meter draws 3,6A ((60*60)/1000). I have 14 stairs, each needs about one meter of strip. 14 meters times 3,6A equals 50,4 amps.

I do not know much about this wire thickens and stuff. So i used a online calculator that said they would have to be 150mm, that is to thick . And since the wire gauge apperently have to be that much. I am afraid of burning the power rails on the LEDs if i connect them in series. 
The last alternative i can come up with is to connect them all in parallel (except for the data line of course). The problem here is again the wire gauge. I am so unsure of what i should do.

One point here for not using one power line to each strip is cost. Wire is more expensive than i had thought of before i started this project. I am trying to hold the price under a 1000NOK (Approx. US$120). Which means that i cant blow $50 on wiring.