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### Topic: [Help] Circular LED Matrix for Railroad Signal Post (Read 723 times)previous topic - next topic

#### noiasca

#15
##### Jul 29, 2019, 01:00 pm
frankly spoken: you not at all. Choose an appropriate micro controller with enough resources for your project.

Start with a small prototype on an Uno. You will get experience and you can calculate how much memory you will really need.

Quote
you could have an array that gives the pixel positions for each "circle" that needs to be lit up,
that was my idea also. Nevertheless, he will need to store each ligthed LED, given the examples I estimate  around 50 per small circle. Plus some color information. Multiplied by the maximum amount of circles, multiplied by the total number of patterns...
DE: Wie man Fragen postet:
1. was hat man (Sketch und Hardware)
2. was SOLL es machen
3. was macht es: IST (Fehlverhalten, Fehlermeldungen, Serial.Output ...)
4. Eine Frage stellen bzw. erklĂ¤ren was man erwartet

#### david_2018

#16
##### Jul 29, 2019, 02:01 pm
fevertheless, he will need to store each ligthed LED, given the examples I estimate  around 50 per small circle. Plus some color information. Multiplied by the maximum amount of circles, multiplied by the total number of patterns...
The example sign has a total of 13 different small "circles", a few of those appear to be in the same position on both the top and bottom sign, so possibly could be reduced to 9.  With 50 LEDs per circle, a 2-dimensional array of integers giving the pixel positions would be at most 13 * 50 * 2 bytes = 1300 bytes, and could be stored in program memory.  If the real sign has a fixed color for each circle, then for each light pattern you only need to store whether the circle is lit or not, so a 16-bit value can store that information using each bit to represent a circle, and storing the actual color information separately.  I don't have time to research it at the moment, but I'm sure someone has found a way in either fastled or adafruit neopixel to use the same led buffer for multiple strings of pixels, so you could also same some memory doing that, since this sign is very unlikely to need to be updated at extremely rapid intervals.

#### V4D3R

#17
##### Jul 29, 2019, 02:59 pm
For now I'd say around 1,800 (600 per head and 3 heads total)

#### V4D3R

#18
##### Jul 30, 2019, 05:18 amLast Edit: Jul 31, 2019, 06:52 pm by CrossRoads
I posted two days ago about making a railroad signal post using a circular matrix. I made some graphics in order to convey the plan easier so more people can help out with how I'd go about this. Attached is a revised matrix (still a 10" circular head but with WS2812B SMD LEDs instead and with a lower count), an NJT type signal and an Amtrak type to show how I'd like to have the heads lit.

Layout:

NJT Type Signal:

Amtrak Type Signal:

I'd like to know how the three heads would be wired to the Arduino and basically how to program them for my requirements. Thank you.

(updated with img tags by moderator)

#### V4D3R

#19
##### Jul 30, 2019, 05:28 amLast Edit: Jul 31, 2019, 06:51 pm by CrossRoads
Wasn't sure if the images uploaded in the post so here's a download for the post layout.

(posted with image tags by moderator)

#20
##### Jul 30, 2019, 06:07 amLast Edit: Jul 31, 2019, 06:50 pm by CrossRoads
Making a 10" PCB with a boatload of WS2812Bs would  be pretty straightforward.  I made a 24" x 9" tail light display for a customer with 192 RGB LEDs and multiple distributed 12V to 5V power supplies on the back to keep the supply logic small.  I'm not going to try and count  how many LEDs you have there. Post a quantity per line  using 5050 WS2812B LEDs.
Datasheet here  http://www.world-semi.com/Certifications/WS2812B.html

Here is a section of the board showing several rows with a 0.1uF cap per IC, dataline connected chip to chip, and fingers of power trace to power all chips. Gnd is not shown, but is everything that is not trace.

There is room to tighten it up some as can be seen.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### david_2018

#21
##### Jul 30, 2019, 06:16 pm
If you don't want to make a pcb, 100 pixel per meter strip would give you nearly the correct spacing.

One major consideration,  each pixel will need around 60mA at 5 volts when fully turned on, so 422 per panel and 3 panels will need considerable power.

#### Paul__B

#22
##### Jul 31, 2019, 09:45 amLast Edit: Jul 31, 2019, 09:48 am by Paul__B
One major consideration,  each pixel will need around 60mA at 5 volts when fully turned on, so 422 per panel and 3 panels will need considerable power.
Only if many are turned on.

However it seems the idling current is not entirely insignificant.  Remember to provide multiple parallel feeds to the power strips, every row and preferably both sides.  Keep data interconnects short, do not take from one end back to the start but "zig-zag".

#### david_2018

#23
##### Jul 31, 2019, 12:31 pm
Only if many are turned on.
It was mentioned that one way of using this would be to have the entire matrix lit up, and with potential outdoor use at considerable distance probably at a high brightness level.  Maximum current would be a bit over 25A per panel, but the actual current needed would depend greatly on the color and brightness levels.  Mainly wanted to point out that battery power was probably not a good option.  With the Amtrak style sign, with what looks like approximately 18 pixels per small "circle", and two of those lit at once, around 2A per panel would be a reasonable estimate, but the power supply has to be able to handle the maximum.

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