I have seen many times the project on Instructable, and I wanted to build mine.

NB: Last time I used a soldering Iron was when I was 14, so 10 years ago.

Let's go step by step.

Pix

Pix

Find the table

Ikea Table, the chepest that you can find.

Plan the size of your matrix

Electrical constraint

Led strip: WS2812b.

  • 5 V
  • Each led needs between 30-60 mA

Usualy, power supply can give you 3A.

$\#LED = \frac{Power}{LED_{consumtion}}$

$\#LED = \frac{3 A}{30 \sim 60 mA/LED} = 50 \sim 100 LED$

As you may not want to light your room with your table, it is okay to not fully supply your LED. Led intensity can be turned from 0 (RGB(0, 0, 0)) to 100 (RGB(255, 255, 255)). We can choose to lower the power supply.

MaxPow = U × I = 5V * 3A = 15W

Looking at supermarket Light bulbs, power is in range of 13 to 26 W. So it is not so huge.

Geometrical constraint

The table has a fixed size, 55 × 55, with 5 cm of borders on each side, leading to a working area of 45 × 45.

Led strip has multiple led spacing format:

  • 30 LED/m 3.3 cm/LED
  • 60 LED/m 1.6 cm/LED
  • 100 LED/m 1 cm/LED
  • 144 LED/m > 1 cm/LED

As the strip has a width of 1cm, and that I expect regular spacing in both width and height, the strip of 144LED/m is discarded (plus, it would be uneasy to manipulate).

$NLED = Length LED/m

In 45 cm, I can put:

  • 13.5 LEDs using the 3O LED/m
  • 27 LEDs using the 60 LED/m
  • 45 LEDs using the 100 LED/m

Total, using the same number of columns and rounding down:

  • 169 LEDs with the 30 LED/m
  • 729 LEDs with the 60 LED/m
  • 2025 LEDs with the 100 LED/m

Even with a margin of error, the last 2 options would need too much electrical engeneering for a starter project.

Odd or Even

In informatic, it is easier to work with number that can be express as a power of 2, like 21 = 2, 22 = 4, 23 = 8, 24 = 16, ..., because of the writing in binary form and the possibility to use corresponding operator.

13 nor 12 is easily writable on a binary format. Let's drop this consideration, or choose your table to be 8 × 8.

From here, the programming part does not differ at all. The only thing that matter is: Do you want the symmetry to be centered on a point (Odd choice) or on a cross (Even choice). That is up to you.

I choose the Even choice, because I wanted a additional margin for my LEDs.

Order everything you would need

  • Raspi Zero (enough, but V3 faster. Easy to change it at anytime)
  • Ikea Table (55x55, the cheapest classic one)
  • Led Strip WS2812b, 5 meters, 30Led/m (Total: 150 LED on it, we will use 144 LEDs)
  • LED wire (Only if you want to reuse the strip at some point. Else take normal soldering wires).
  • mini USB b to circuit (For supplying electric current by an external source)
  • 2 Power supply:
  • One for the Pi (5V, small amp)
  • One for the LED strip (5V, max amp, 3A or more, 144 * 50mA = 7.2A (Not supplyable easily. 3A gives correct results. You are not building a lamp for your room))
  • Breadbord, cables
  • Plexiglass 50 x 50, 3mm or around, depending on if you want to put stuff on your table or not. Thinner: cheaper, but not that solid, Thicker: expensive, increase oppacity.
  • Cartwood
  • bolt

Tools

  • Soldering Iron + Soldering Metal + Soldering grapper
  • Dremel + cutting disks
  • Cutter
Pix

Pix

Deconstructing the table

  1. Cut the top of the table.
  2. Remove the filling cardboard.
  3. Create a cardboard matrix

Pix Pix

Pix Pix

Isolation matrix

The goal is to obtain one pixel per led, not a mix. Each LED must have its compartment.

On the net, you would find 2 possibilities: cardboard and wood options. If you have a laser cutter, use it to go fast on this step, and take wood for solidity. If not, use cardboard and cut with hand cutter (takes a lot of time, be patient).

Pix Pix

Assemble the matrix

And test that it goes into the table without forcing.

Pix Pix

LED soldering

Pix

Pix

Transform your LED strip into a LED matrix.

Cut every 12 (depend on your choice) LED the strip.

2 Options:

  • Solder amovible connector
  • Solder each substrip with direct wire

I choose first option, but it is up to you.

Amovible connector

Pros

  • If one sub LED strip fail, you can replace it easily by disconnecting it from its neighborhood
  • Easier soldering (as you manipulate 12 LEDs at a time)
  • Possibility to test the solders of each strip separately

Cons

  • Connector take non negligeable space on the border of the table.

Direct soldering

Pros

  • No specific material needed
  • Take less space

Cons

  • If one substrip fails, it needs more work to replace it
  • Manipulation of whole LED matrix is hard

Pix Pix Pix

Pix Pix

Check that soldering are working

Check connection

Check connection

Put the leds

Trace the grid

Put lines where you will put the strips. Parallel, regulary spaced. Don't think that you are better than you are. Error propagation is very common.

Drill connection hole

I will put my Raspberry Pi BELLOW the table, as there isn't much space left above. Need a hole for the 3 cables (data / ground / 5V).

Glue strips to the table

Strips usually have 3M sticker under it. It is not very performant for led. But as you will put the matrix above, this is not a big deal.

Be carefull: Zigzag the strip, else the connector won't fit.

Pix Pix

Wire the strip

As discussed in the introduction, the LED strip need a sufficient power supply. The Raspberry used is not strong enough for that.

You need to put an additional usb plug (or other, but it is easier to find a cable that match).

To simplify the scheme:

  • Pi Ground <-> USB ground <-> LED strip ground
  • Pi Data <-> LED strip data
  • USB 5V <-> LED strip 5V

Put the matrix

Nothing to say about. Connect the LEDs if not done before.

Put the plexiglass

Put a sulfurized paper to opacify the glass. That allow to avoid direct light from the LEDs.

Pix Pix


 Coding part

Pix Pix Pix Pix Pix

Working with matrix

The basic LED strip library GitHub, where the basic command turn on pixel by giving a tuple (position, (r,g,b)).

For the zigzag matrix, the only thing to do is to build a class of higher level which turn on/off pixels by taking a tuple ((row, col), (r,g,b)) that call the lower level API by converting (row, col) into position. The maths are easy ! Just draw on the paper.

Simulator

The goal was to be able to test pattern without using the table, by displaying in my computer screen.

I tried to used Qt for that purpose. That worked initialy, but as the refresh rate was high, it quickly failed.