Design Sewing Electronics

This instructables show some design details when I design my sewing electronics.

Note:

You can find much more design details in my Twitter.

• Conductive thread
• Any textile, it is Sport Loop for 41mm Apple Watch in my project
• Sew Friendly modules

Sewing Electronics, or called e-sewing, is a special category that can build circuit with sewing only.

The prerequisites are all electronics components are in module form and the breakout pins are sew friendly.

Sewing use conductive thread to connect the modules together, so you don't need soldering skill for building circuit.

Ref.:

https://www.sciencebuddies.org/blog/sewing-electronics-wearables-that-light-up

https://learn.sparkfun.com/tutorials/lilypad-basics-e-sewing/all

http://sewelectric.org/diy-projects/sparkling-bracelet/design-your-bracelet/

If you search "e-sewing" on the web, you can find various sew friendly modules. You can build many simple circuits with those modules.

Then you need to fix the modules on textile and connect the module pins to build a circuit. The conductive thread can do both jobs at the same time.

note:

If you cannot find the desired e-sewing module on the web, you can design a module PCB yourself.

Nowadays, design your own PCB become is very easy. You can order the designed PCB on the web and even SMT service! So you can have your own PCB even you don't know how to soldering.

For reducing the sewing complication, design sew friendly module should minimize the number of connection between modules.

NeoPixel is one of the key component to meet this goal. It only requires 5V and GND power pins and a signal pin for driving it. Then you can add as much as LEDs you want on the PCB in series to form a LED matrix.

Here are some videos I design LED matrix PCB previously:

https://www.bilibili.com/video/BV1fh411M7CJ

https://www.bilibili.com/video/BV1Ua4y1N7UA

https://www.bilibili.com/video/BV1QM4y1C74U

https://www.bilibili.com/video/BV1us4y1N7gB

https://www.bilibili.com/video/BV1nc411n76h

In this project, I would like to build a wristband with watch function. And also some lighting effect for decoration *v*

I am familiar with ATtiny NeoPixel library in my previous project, so I selected this microcontroller. And also it need a RTC chip for time keeping, a connector for battery power and a button to activate / switching display function.

Main board can be much complicated. Before actual order your design PCB, it is better build a PoC first. So you still need a circuit prototype in the middle.

Wearable is powered by battery and the power consumption is critical for the battery life.

Assume you want a 500 mAh Lipo battery can last a week, theoretically the average power consumption should be: 500 mAh / 7 days / 24 hours ~= 2.9 mA

According to various Neopixel data sheet, the standby current for a pixel is below 1 mA. But accumulate 100 pixels will over 50 mA. It is much more than the design limit, so it need some circuit cut the power while standby. My design use a GPIO and NPN transistor to control the NeoPixel power supply.

The ATtiny family can go to sleep mode to reduce power consumption and most RTC chips designed low power consumption. As show in above video, the power consumption can cut to below 1 mA while standby.

This project use an Apple Watch Sport Loop as the textile base. It requires some patch before using it.

I selected a 500 mAh curved Lipo battery, it is slim enough to hide at the wristband back.

The sewing connection is straight forward.

Simply connective the positive and negative pins with individual conductive thread. Then connect adjacent signal pin pair one by one.

Note:

The signal pins are near the negative pins, please beware do not touch each other or it will short circuit and not working.

The font size for this project is very tiny, only 3x5. It is hard to find a standard font for it. So I write a simple web page interface for designing it:

https://moononournation.github.io/Font-Stuff/FontDesign.html

After you design the font, simply copy the output code to your Arduino project.

Besides watch mode, I would like the wristband can be a fancy accessories. So it also have a rainbow mode *v*

This project still in prototype status. It is not yet have upload program interface yet, so it need an ISP programmer in the middle to do the job.

You can find my work-in-progress source code at Github:

https://github.com/moononournation/NeoPixelMatrix.git

• Battery Charging circuit?
• Upload program interface?
• More fancy mode?
• Wireless connection? WiFi? BLE?
• Crow funding? (The prototyping of NeoPixel PCB is really really high, it need someway to reduce it)