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Smart sequins



In the article, I’ll talk about how we developed a miniature electromechanical color reproducing device for smart clothes and adaptive camouflage systems.

Prologue

“She began to climb up the tree trunk. The mechanisms of the suit immediately set to work, painted in the color of a tree bark, speckled with specks of moonlight. "

Scott Westerfield Special

After reading these lines, my imagination was captured by this idea! A suit that is able to adapt to environmental conditions, change its color, pattern, texture. Great optical camouflage system. And besides, clothing that can change the appearance at the request of the owner or depending on its physiological parameters.
"He wore a polycarbon chameleon suit, capable of reproducing any gamut of shades by the mental order of the owner, expressing changes in his mood."

Ulyam Gibson "Neuromantic"

Authors of works of literature and cinema use chameleon costumes as they like. But are there any real developments in this area?
A review of the literature showed that different countries are developing adaptive camouflage systems, and a variety of color reproduction devices are used:

  • polymer LED matrix (PLED displays), 2011, CAMELEON system;
  • heat-sensitive polymers , in 2014, researchers from the University of Houston published the results of work on the creation of a matrix of elements that can change their transparency when heated;
  • transflective displays , in 2015, Folium Optics introduced a working prototype at the DSEI international military technology exhibition.
  • electroactive polymers , in 2018, Russian developers presented a working prototype at the Army forum.

But almost all developments are at the stage of laboratory tests and prototypes.

In the process of finding ideas for implementing something similar, I came across something new.
Once they asked me: “Do you know what sequins are?”

This is where the development story begins ...

Sequin


In the beginning, when I told my friends and colleagues about what I was doing now, they stopped my story at the very beginning and asked the same question: “Sequins?”
Therefore, I will immediately explain what is at stake.

Sequin (French “golden grain of sand”) is a decorative element of clothing, which is a small circle of plastic (flake), having a small hole offset to the edge, used to fix it (by sewing) on ​​a fabric or other material.



Moreover, these plastic circles have a “trick”, they can rotate (scroll), showing the observer one or the other side, which can be painted in different colors.

In general, it seemed interesting to me. Cloths of sequins reminded me of LED displays, only with low resolution and poor color reproduction. But on the other hand, they work on reflected light and are placed on a flexible basis (clothing or its elements).

It would be cool to create a sequin that can independently “leaf through” and change the color that is currently being shown to the observer. Many of these devices will be combined into a matrix capable of reproducing various patterns, displaying text, pictures, and all this in dynamics!

Electronic sequin


To begin with, several sketches were made and the technical requirements for the future product were formulated:

  • use at least 2 colors;
  • sizes are comparable to real sequins;
  • light weight and power consumption;
  • .

1


Each electronic sequin consists of a base with which it is attached to a future base (fabric). On the base is located electronics, for control, and petal drives.

Petals are located on the same axis.

It was decided that the first version will have 3 colors:



For the first prototype, size is not the most important thing, so let the sequin be a little larger than what was specified in the statement of work.

The structure of the electronic control unit:



ArduinoNANO platform is selected as the controller. Torque from the motors (collector motors) to the sequins will be transmitted through the worm gear. As the sensors for the position of the petals, variable resistors are used, obtained from small SG90 servos.

It works like this:


Everything is as it should! The only thing that did not please was the low speed of the petals, but for the debugging process it is. Moreover, we corrected this trifle in the next prototype.

Version 2


In the new model, we only changed the composition of the electronic control unit and added a printed circuit board so that the sequin turned into a full-fledged module. Now everything was controlled by an 8-bit ATtiny44 microcontroller via the L293DD engine driver.

This is how it looks:



And this is how it works:


As you can see, there is no talk of any digital data exchange protocol so far. First you had to deal with mechanics.

Version 3


In the next version, we set ourselves the task of increasing the number of reproducible colors to 5. To do this, we need to increase the number of petals to 4, and make them alternately flip through one and the other. The easiest way, obviously, is to increase the number of drives, but in this case it is necessary to place as many as 5 motors on the sequin! This is an increase in weight, dimensions, complication of the electronic control unit. We decided that this is the wrong way.

To achieve the result, we tried various ways. One of the first and most interesting, as it seems to me, is to use the torque of only one engine to drive the petals through mechanical gears.

This is how the first prototype we assembled looked like:



And it worked:


Of course, neither speed nor rotation angles are calculated in this demo model. It seemed to us too complicated, yes, and a large number of mechanical components would be difficult to implement for smaller dimensions. Nevertheless, this option was worked out.

Ultimately, we settled on this scheme:



In fact, we saved the electronic control unit from the first prototype, but changed the roles of the motors, added mechanical components and replaced the position sensors of the lobes with optical limit switches. It was decided to use the torque of one motor, and with the help of a gearbox (transfer case) to deliver it to each petal in series. The current “transmission” was monitored using a slide variable resistor.

This is what the new mechanism looked like:



Oddly enough, it worked not bad:


But still he has more disadvantages than advantages:

  • a large number of mechanical gears (low reliability);
  • many sensors need to be calibrated;
  • large dimensions;
  • low speed of movement of the petals.

Realizing that at this stage we can not offer any alternative, we began work in a different direction.

Smart Sequin


Finally, we decided to seriously take care of the size of our sequins. It is necessary to at least get closer to the dimensions of these decorative elements of clothing. And we made it much smaller: The



number of reproduced colors was reduced to 2, like a real sequin. A miniature stepper motor was taken as the drive for its only lobe ( I wrote about it in detail here ).

The value of the switching time between colors is obtained by simple calculations. The motor takes 8 steps with a pause between steps of 10ms. The calculation allows you to only approximately estimate the switching time.

The quiescent current is still a significant amount, but if you use the low power modes of the controller and driver, you can reduce this value.

The new structure of the electronic sequin control unit:



We decided to keep the element base with the ATtiny44 controller and the L293DD driver.

Schematic diagram of the device:



A small printed circuit board was laid out for sequins:



Due to the small size of the device, we had to place microcircuits on both sides of the board, in fact, they occupy almost all the space on it. It is necessary to change the element base ...

Appearance of the board and sequin assembly:



Soft


It seemed to us that it would be very convenient if the sequins behave similarly to the LEDs in the address LED strip. Therefore, the data exchange protocol was implemented accordingly. The matrix control controller drives a bit stream for all matrix elements on the bus, framing the package with start and stop dividers. In the inactive state, the line is pulled up to Vcc.



Since these sequins reproduce only two colors, only one bit is allocated for each in the package.



The first sequin in the row notices the start separator, reads the first bit intended for it, and transfers the rest to the second without changes. The second sequin in the row again reads only the first bit and transfers the rest further down the chain. Thus, it is possible to connect a large number of modules with the ability to control each separately, without resorting to addressing.

Bits follow one after another at regular intervals. The duration of the high logic level determines “0” or “1” is encoded by this pulse. All procedures related to the exchange of data in sequins are implemented through interrupts. The start separator is fixed on a falling edge on the PA3 line (external interrupt), then a timer starts, which generates interrupts at regular intervals. In the timer interrupt handler, time intervals and pulse durations are counted.

They didn’t open anything new, and it is unlikely that anything else could be invented for a single-wire interface.

The Arduino platform, which communicates with the computer, acts as the matrix controller (or better to say the tape) of sequins. We wrote a small application in the Processing environment, which allows using a matrix of 4 sequins using a graphical interface:


About functionality


Let’s think about the advantages that clothing that can change its color through the use of electromechanical sequins can give.

The first thing that comes to mind is the use of sequins in the design of modern clothes. If you look for a little information about trends in modern clothing design, you can often find the phrase “smart textile”, “smart fabrics”, a lot of references to fashion designers who print their outfits on a 3D printer and other technological wonders of the fashion industry. I believe that electromechanical sequins fit very organically into this concept.

Another application is adaptive (active) camouflage systems, as noted above.

In addition, each sequin petal can have a glossy or matte texture, and is painted in different colors, which means that the sequin will absorb solar radiation in different ways. Thus, the owner of clothes covered with such sequins, it becomes possible to control their microclimate.



In addition, the lower petals can have special “pores” that can open and close with the upper petals, through these “pores” excess moisture can evaporate.



At the same time, if it rains outside, then the sequin can reliably close the “pores”, preventing moisture from getting under the clothes.

Few numbers


Suppose we have already managed to solve the problem of placing electronic sequins on an elastic material, or, we created some kind of “mechanical canvas” from these small devices. What characteristics will the canvas have (at this stage)?

Estimate the cost of manufacturing one sequin.

Notes:

1. Retail price - the average retail price for electronic components in my city.

2. Wholesale - ordering electronic components in batches from China.


* sheet 208x248mm - 216 rubles. (Slist = 51584mm ^ 2), S-boards = 391mm ^ 2, N boards on the sheet = 51584/391 = 131pcs, the cost of 1 board = 1.64 rubles.
** coil 1kg -1000 rub., cost of 1 set of parts = 1 rub.

It turns out that in mass production the cost of one element is slightly less than 100 rubles.

We will calculate the required number of sequins to create a canvas with an area of ​​1 m2:

  • The area of ​​one sequin S1 = 391mm2
  • Blade area Sp = 1000000mm2
  • The number of sequins on the canvas N = 2558pcs
  • Weight sequins m1 = 3.5g
  • The mass of the canvas with an area of ​​1 m2 Mp = 8951 g
  • The prime cost of a cloth with an area of ​​1 m2: 240306 rub
  • Power consumption at rest: Imin = 76A
  • Power consumption while switching all web elements: Imax = 306A

Eh ... do not sew us dresses from electronic sequins ...

findings


Here you can smoothly proceed to the conclusions, and talk about the disadvantages of using electromechanical color-reproducing devices in general, and in particular our sequins.

Are common


  1. The presence of moving parts, vulnerability to mechanical damage, low reliability of individual matrix elements, vulnerability to pollution.
  2. A small palette of reproducible colors.
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In general, the thought was good, the implementation turned out to be less good ... Nevertheless, work on “smart sequins” continues. Soon we will try to place them on clothes, and we will definitely share the results.

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