What Are Soft Circuits?
Chances are, if you are entrenched in e-textiles like us, you are familiar with another term: “soft circuit.” It’s a term that is used interchangeably with e-textiles and describes the soft and flexible portion of the circuit, more-so than the electronic portion of the circuit.
Defining soft circuits
Soft circuits are electronic circuits with “soft” properties. This often means they have multi-axis flex and can be draped and folded in ways that something like a Flexible PCB often can’t. While many imagine circuits sewn with conductive thread when they think of soft circuits, they can be so much more than just LEDs on felt. They can be made of various different electronic components and conductive materials—some of which we will get into later.
Functionality of soft circuits
There are two main categories of soft circuits. One involves attaching electronic components to the soft conductors, and the other involves creating components from the conductor itself. We call these attached and embedded components, respectively.
Soft circuits with embedded electronics – This type consists of attaching motors, LEDs, and sensors onto a soft flexible substrate to create a sort of “hybrid” circuit.
Soft circuits as embedded electronics – This type uses the conductive pathways to create new electronic components like antennae, heaters, and capacitive touch sensors. All of which, can be added to applications such as wearable technology.
Now that you know the basics of soft circuits, let’s dive a little deeper and review the functionality of the components:
Conductive Materials – Flexible, stretchable and soft conductive materials are at the heart of soft circuits. They are the pathways that connect the electronic components (LEDs, sensors, etc.) to one another. Conductive ink and conductive thread are both popular choices, and they are typically made from metals such as copper or silver.
LEDs – LEDs are used to illuminate a product, and are typically covered with another layer of fabric.
Sensors – Sensors are commonly used in active e-textiles, and there are three main types used in wearable technology: Capacitive, Resistive, and Optical. These sensors can sense touch (pressure), temperature, and strain (movement).
Batteries – Each e-textile or soft circuit needs a power source. To achieve this, once can select from a wide range of batteries on the market from 110mAh coincells to 5V powerbanks and beyond.
Microcontrollers - A microcontroller is an integrated circuit that is designed to control the input and output of an electronic device. In soft circuits, they are used to power the various components that are embedded.
How to sew a soft circuit
One of the more common and accessible methods of building wearable electronics is to sew the circuit by hand. It may be a bit tedious, but it is a process even budding creative technologists can learn! For this, you will need a piece of felt, conductive thread, a sewing needle, and fabric glue. As for electronic components, you will need a resistor, coin cell battery, and a 5mm LED (which is optional). This is also a great way for young ones to learn how electric currents work.
Check out the full tutorial on Instructables!
Applications
There are a few key applications of soft circuits that we would like to cover, each involving different electronics and capabilities.
Medical wearables
Soft circuits can be integrated into a wide variety of medical wearables. Sensors are the most commonly used electronic component for this application, and they can be used to measure heart rate, monitor blood pressure, and have even been able to collect data from sweat to notify the user of problems such as electrolyte loss and dehydration. The Loomia Electronic Layer (LEL) has several capabilities when it comes to medical wearables, such as electrode integration for monitoring, and data buses for easy communication between patient and physician. This technology can make healthcare easier for the elderly who cannot travel to a doctor easily, or those who are entirely home bound due to their condition.
2. Automotive and aerospace interiors
In automotive interiors, soft circuits can be used to heat seats and steering wheels, as well as cabin lighting and user interfaces. Some commonly used electronics for these applications are sensors, LEDs, and transistors. Research is currently being conducted on soft circuit applications in the aerospace market, and heated seats on commercial airlines might come sooner than you think. Fun fact: the LEL can heat interiors up to 200 degrees Fahrenheit, and our soft switches have been tested for 10,000 presses!
3. Outdoor gear
Soft circuits have two main applications in outdoor gear: in-garment heating and in-garment lighting. Each of these applications contain biosensors and LEDs. Our LEL, for example, is fully customizable for both and can be seamlessly integrated into jackets, gloves, boots, and even camping equipment such as tents and sleeping bags. So, if you are in the dark woods at night, you can rest assured you will be kept safe and warm.
Over the next few years, we hope to see soft circuits in more everyday products; from the most basic items like our clothing, to the cars we drive. However, with this will come more strict regulation. The Association Connecting Electronics Industries (IPC) released their E-textile Standard, IPC-8921, just last year. This standard was developed with the help of the Textile Materials Subcommittee, and it establishes classifications for e-textiles integrated with e-fibers, e-yarns, and sets a standard for durability testing and other test methods. To learn more about the IPC-8921 and what it covers, read the press release here.