A single strand of thread, coated and stitched into a shirt, can track your breathing while you wear it. No wristband, no charger to remember, no rigid gadget clipped to your belt. Researchers at Tufts University have built working circuits directly onto textile threads, and the result behaves more like fabric than like the electronics you are used to.

Their thread carries complete analog circuits: transistors, resistors, sensors, and amplifiers, all riding on one strand instead of a flat circuit board. Because the components sit on the thread itself, the circuit can bend, twist, coil, and stretch while it keeps working. In one demo a thread near the temple picked up blinking. Another placed near the diaphragm followed breathing patterns and respiration rate, close enough to fabric that a wearer would forget it was there.

How the thread becomes a circuit

The wiring is a thin thread coated in gold. Tiny flexible organic transistors attach straight onto it, and conductive polymer coatings form the electrical pathways and passive parts like resistors. A soft material called a eutectogel acts as each transistor's gate dielectric, steering current the way the gate on a normal MOSFET would. Unlike the hydrogels most flexible electronics use, eutectogels do not dry out, and they partially heal themselves: bring a torn section back together, add gentle heat, and both the mechanical strength and the electrical performance return. The on-thread amplifier lifts the tiny signal from a stretch sensor with no rigid board anywhere in the loop.

Build your own e-textile version

You will not spin gold thread at home, but sewable electronics is very approachable for a classroom or capstone project. Start with a LilyPad-style board, which runs its ATmega328 at 8 MHz on 3.3V from a 3V sewable coin cell, and stitch your traces with conductive thread instead of soldering wire. A few gotchas to plan for:

• Conductive thread has real resistance, a few ohms per inch, so keep runs short and never let two bare traces cross.


• Sew a stretch or bend sensor into a sleeve and read it on an analog GPIO pin to log movement or breathing.


• Seal every knot with a dab of clear nail polish so it will not fray or short after a wash.

Read the original write-up on Hackster at https://www.hackster.io/news/your-next-health-tracker-could-be-a-piece-of-string-b6a43091534d, then grab conductive thread and a LilyPad from circuit.rocks and prototype a breathing sensor on an old t-shirt this weekend.

Originally published on blog.circuit.rocks.

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