Model BANNED control board with NeoPixel

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jlucb
 
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Model BANNED control board with NeoPixel

Post by jlucb »

Hello,

I am designing a display and control board for my model BANNED. I purchased NeoPixel LED strips with 60 pixel/meter and a 24 pixels ring for the turntable. The board is 663mm wide and 250mm height. I plan to use ~300 LEDs arranged in 3 strips.

Here is the drawing :
- each grayed square is a WS2812 LED location. When on a white background the LED is actually there. Strips are laid horizontally
- colored lines are data connections between the strips.

Image

Link to a bigger picture

The LED will be used at a maximum luminosity of 30%

I read a 1000µF capacitor should be put on the VDD-GND lines of LED.

Before starting to build the board, I have a few questions :

Since I will only use the LED at a maximum luminosity of 30% do I need such a big capacitor ?
Is it better to spread lower value capacitor (100µF for instance) along the strips ?
What is the maximum length of a data wire (the system will be used in an environment with electrical noises coming from the motors of the locomotives) ?

Best regards

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adafruit_support_bill
 
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Re: Model BANNED control board with NeoPixel

Post by adafruit_support_bill »

Since I will only use the LED at a maximum luminosity of 30% do I need such a big capacitor ?
The capacitor is primarily intended to help filter any power-up spike that might come from the power supply. These vary from non-existent to dangerous, depending on the supply, and may change as a supply ages. The large value was chosen as 'safe' value and relatively inexpensive insurance.
Is it better to spread lower value capacitor (100µF for instance) along the strips ?
This is also a good approach.
What is the maximum length of a data wire (the system will be used in an environment with electrical noises coming from the motors of the locomotives) ?
People have gone very long distances using cat-5 wire and RS-485 drivers. There is a post on the forums here detailing that. But you should be able to drive up to a couple of meters direct from an Arduino pin. Given the long lines and electrically noisy environment, it would be wise to take some additional precautions to minimize ringing and safely dissipate any noise induced on the line: Use the recommended 300-500 ohm termination resistor on the signal wire at the head of the strip. Also add a 10K ohm resistor between DIN and GND at the head of the strip.

Nice looking control board by the way. What are you modeling?

jlucb
 
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Re: Model BANNED control board with NeoPixel

Post by jlucb »

Hello

Thank a lot for the answer
adafruit_support_bill wrote: The capacitor is primarily intended to help filter any power-up spike that might come from the power supply. These vary from non-existent to dangerous, depending on the supply, and may change as a supply ages. The large value was chosen as 'safe' value and relatively inexpensive insurance.
Ok, I use a 5V 20A industrial switching power supply from ENSTICK.

Use the recommended 300-500 ohm termination resistor on the signal wire at the head of the strip.
Usually a termination resistor is put on a differential pair of wires. On what other wire should I connect the resistor ?
Nice looking control board by the way. What are you modeling?
It is to control and display the state of my model BANNED. Thin blue lines represent 32 X-Y IR-LED/phototransistor barriers (20 in X, 12 in Y). A program on a PIC 18F26K80 scans the IR-LED/phototransistor pairs and detects the position of the finger (at each thin blue line intersection). WS2812 LED are driven by an Arduino Pro Mini. Some LEDs correspond to buttons to control the turnouts, the turntable, the uncouplers and so on (so they are located on IR barriers intersections). Some others only indicate if the corresponding tracks are powered or not, if there is a train on it, what track are connected according to the position of the turnouts. The PIC is connected with a CAN bus to the rest of the system, gets command from it and sends the "clicked" IR barriers intersections. The Arduino communicate by SPI with the PIC and the later forwards the commands to the Arduino. I had to design a dual processor board because the Arduino cannot be interrupted when it refreshes a LED strip.

Best regards

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adafruit_support_bill
 
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Re: Model BANNED control board with NeoPixel

Post by adafruit_support_bill »

Ok, I use a 5V 20A industrial switching power supply from ENSTICK.
Not familiar with the brand. But we have seen damaging startup spikes coming from lab supplies from respected makers.
Usually a termination resistor is put on a differential pair of wires.
They are also used in single-ended configurations such as this one.
It is to control and display the state of my model BANNED.
My question was about your BANNED. What are you modeling? Judging from the turntable, I'm guessing steam era?

jlucb
 
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Re: Model BANNED control board with NeoPixel

Post by jlucb »

adafruit_support_bill wrote:
Usually a termination resistor is put on a differential pair of wires.
They are also used in single-ended configurations such as this one.
Okay. So I connect the 500kΩ resistor between DIN and ? GND ?
My question was about your BANNED. What are you modeling? Judging from the turntable, I'm guessing steam era?
Yes. It is an early epoch II German (DRG) layout (1923 - 1930)

Best regards

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adafruit_support_bill
 
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Re: Model BANNED control board with NeoPixel

Post by adafruit_support_bill »

Okay. So I connect the 500kΩ resistor between DIN and ? GND ?
The resistor should be in series with DIN. See the post from adafruit_suport_mike in this thread for an explanation: http://forums.adafruit.com/viewtopic.ph ... or#p258528
Yes. It is an early epoch II German (DRG) layout (1923 - 1930)
Nice! What scale are you modeling? Most of my train control work has been in 1:1, but I have done some in G and my son has quite a collection of Japanese N-scale.

jlucb
 
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Re: Model BANNED control board with NeoPixel

Post by jlucb »

Hello

It is a N-scale layout. I have not enough room for a larger scale :)

About the serial resistor. Should it be close to the first LED of the strip or may I put it on the control board ?

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Re: Model BANNED control board with NeoPixel

Post by adafruit_support_bill »

The resistor should be close to the first LED.

jlucb
 
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Re: Model BANNED control board with NeoPixel

Post by jlucb »

Thanks !

Here is the arrangement I chose. I would like to be sure I am not missing something.

I divided my ~270 LEDs in 6 blocks, each having < 50 LEDs. Each block is powered by a pair of wire going to a connector (6 connectors available, 7A max each). So each block should draw about 3A at most. I will use 0,5mm2 wires with about 20cm between the connector and the LED strip..

I designed a 100mm x 20mm board to put the connectors and dispatch the power from my 5V 20A switching power supply. The board carry 6 220µF capacitors in // (I chose 220µF because I had 25 in stock) for a total of 1320µF to prevent voltage spikes when the power supply is switched on.

I plan to put a thick layer of solder on the PCB tracks (width 4mm) to carry the 18A maximum current. Here is the drawing of the power dispatch board :

Image

Image

K1 is the connector to the power supply. At each end there is a hole to screw the board. These holes are connected to GND and will be used to connect the GND of the LED to the control board.

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Re: Model BANNED control board with NeoPixel

Post by adafruit_support_bill »

That looks like a nice robust design. I don't see any problems with it.

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