Making my own boards to control 'dumb strings'

[Mark_M]

I want to try to keep cost to a minimum because the F48 and 3 differential boards will cost me around $380NZD and I don't want to purchase separate boards to use dumb RGB strips. 2018 I made my own controller using an Arduino with transistor switching boards.

I have 25 boards each with 6 NPN transistors on it (Transistor board.png).

I want to buy a string of pixels without any water proofing on them (PixelNode.png), take out the LED and connect each of the three connection R, G, B to a transistor on my previously made boards (ConnectionIdea.png).

I would then need to tell Xlights that those channels are individual rather than 3 channels making up a pixel. The only main concern I have is that the LED on the board my use a common positive and the chip connects a leg of the LED to negative to turn on (NotIdeal.png), my boards need a positive connection to turn on which will require the nodes board to use a common negative (Ideal.png).



[Edit Jan 2021: The F48 and 4 diff boards cost me $448.24NZD in 2019, so much for being cheap!]

 

[David_AVD]

You can buy the pixel chips (WS2811 for example) by themselves which means you can make your own board with everything on it.

The WS2811 pixel chip is negative switching, so you'll have to use inverters to flip that to positive switching to drive your transistors (or even better, logic level N-channel MOSFETS).

That will give you the high current negative switching you need to drive single channel LED strings or 3-wire 2-channel LED strings.

If you want to keep cost right down, use an Arduino with an Ethernet board and have that drive the N-Channel MOSFETs from that. You will need to do all of the PWM control yourself though and that will be hard for more than a few channels.

 

[Mark_M]

In terms of xLights (and possibly Vixen) can you define a channel as an output?

 

[David_AVD]

Yes, you can very easily define single channel props in xlights. I have them for stuff like lasers, strings, etc.

For the controller, you could buy a 2811DC15 from Hanson Electronics and drive it from a small pixel controller. That way it's easily expandable and you can use the same pixel controller for actual pixels later on.

 

[Pesle]

Ive used an Arduino Nano and SoftPWM library to run 12 channels with PWM pretty flawlessly with ethernet, and its really cheap. Probably wouldnt do many more than 12 channels as i was having some issues with allowing enough of a buffer for the ethernet while having the lights pulse fast enough so that they dont flicker.

 

[AAH]

If you're set on making your own board rather than grabbing 1 of my 2811DC15's or 2811DC30's then I have a few k of 2811 pixel IC's here that I could sell you some of.

 

[Mark_M]

I'll be looking around for purchasing pixels without water proofing. I won't make any promises though, i've still got to decide on the whole cost of changing to pixels yet ( I need these to run lights that won't be changed).

 

[Mark_M]

Thinking about this more, I probably don't need to make many of these boards and I could just use the pixel node boards alone. My lights were previously solar powered or battery and run on 3v. Theoretically the pixels RGB LED is 3v. I could directly hook a string to a colour (R, G or B) from the pixel node board, the only problem is that not all strings would be capable because of the current draw (I would need to test the maximum current draw per colour on those pixel node boards). It would work well for little things like store bought candy canes with 5 LED's in them (there only 20 cm tall).

 

[David_AVD]

There are also solar light sets where LED strings are actually 27V or thereabouts. You'd have to check.

 

[Mark_M]

@David_AVD
The strings I have are all 3v. There was one set last year that I had to leave the solar panels circuit boards with because it boosted to voltage to 70v. I mostly buy battery powered 'seed lights' strings (all LEDs are in parallel), Seed lights are good verses the other style of 5mm LEDs with a bit of heat shrink around the legs because the whole LED is dipped in resin like pixel nodes making them waterproof.

 

[AAH]

A problem with all the leds being in parallel and using a pixel directly is that ws2811 has a design limit of 18.5mA per colour. Depending on the number of leds in parallel this could mean that you will barely get them lighting up as a 10-20mA per led current is fairly typical for leds. If for instance there are 20 leds in parallel the 2811 IC would effectively be supplying each 1 with under 1mA max meaning that they aren't running anywhere near as brightly as they could be.