Tag Archives: 1-Wire

Biosensors you stick to your skin

CBS ran an interesting article about tiny biosensor patches that monitor your health while they are stuck to your arm or leg. The article referenced work done by engineers at the University of Illinois at Urbana-Champaign and Northwestern University. You stick the biosensor to your skin like a temporary tattoo. The work was presented in a paper hidden behind a paywall at Sciencemag.org. The abstract reads:

“When mounted on the skin, modern sensors, circuits, radios, and power supply systems have the potential to provide clinical-quality health monitoring capabilities for continuous use, beyond the confines of traditional hospital or laboratory facilities. The most well-developed component technologies are, however, broadly available only in hard, planar formats. As a result, existing options in system design are unable to effectively accommodate integration with the soft, textured, curvilinear, and time-dynamic surfaces of the skin. Here, we describe experimental and theoretical approaches for using ideas in soft microfluidics, structured adhesive surfaces, and controlled mechanical buckling to achieve ultralow modulus, highly stretchable systems that incorporate assemblies of high-modulus, rigid, state-of-the-art functional elements. The outcome is a thin, conformable device technology that can softly laminate onto the surface of the skin to enable advanced, multifunctional operation for physiological monitoring in a wireless mode.”


This biosensor can monitor your health when adhered to your body.

What was telling about the paper were all the people involved:

Sheng Xu, Yihui Zhang, Lin Jia, Kyle E. Mathewson, Kyung-In Jang, Jeonghyun Kim, Haoran Fu, Xian Huang, Pranav Chava, Renhan Wang, Sanat Bhole, Lizhe Wang, Yoon Joo Na, Yue Guan, Matthew Flavin, Zheshen Han, Yonggang Huang, and MacArthur fellow John A. Rogers.

I am not sure if that is a list of grad student slaves or distinguished professors, but the CBS article neglected to mention that some of the authors represent Tsinghua University in Beijing, Zhejiang University in Hangzhou, and Hanyang University in Seoul. This long list confirms the observation of my pal Ed Fong that system-level design requires engineers that are more social than IC designers and, I suspect, programmers. Ed has done both IC design and worked in complex electro-mechanical systems, so he should know. When you do a complex system like these biosensors it only stands to reason you would need a lot of people involved since there is so much expertise needed in so many areas.


The flexible sensor is like a temporary tattoo, it can bend and flex with your body in order to stay attached and keep working.


Here is a closeup.


And an ultra-close-up.

The new paper implements a complete system based on these biosensors. Adding a power system and a microcontroller and probably a radio is not trivial, hence the large crown of contributors. Another thing that makes me proud of the recent paper is that it has contributors from the US, China, and Korea. That is what I love about technology and engineering. While other industries and politicians give lip service to diversity, the tech industry has practiced it for decades. Here in Silicon Valley every tech company is more like the United Nations. As long as you know what you are doing, you can work anywhere you want, and that is something we all should be proud of.


Here is a biosensor as it would appear adhered to a heart.

Speaking of medical devices, my pal Ken Carroll went to work for Nanostim over 5 years ago. The idea is to make a heart pacemaker so small that you can just attach it to the heart. The wires of a pacemaker are one of the most problematic components, and they wear out and need replacement before the pacemaker battery dies.


This Nanostim pacemaker is 1/10 the size of a conventional one. It is implanted directly in the heart, needing no fragile wires to deliver the pulses to the heart.


Here is the Nanostim pacemaker in-situ.

Ken is a great IC designer, and if anyone can make a chip small enough and low-power enough, he can. I see Nanostim was acquired by St Jude’s Medical last year, so that is good news for all the people that worked for so many years to make this a reality. I have a mechanical engineer buddy that works at a laser eye surgery place, and he tells me it is really exacting work when you have to keep the FDA happy.

Single wire communication, with power too

I don’t like the term “single-wire communication, since you always need a ground path. My buddy Joe Betts-Lacroix worked on a system at IBM Research where if you shook hands with someone, your PDA (personal digital assistants) would exchange information like your business cards. The “one wire” was your handshake, and the return path was your body’s capacitance to earth.

Most times when you see “one wire communication”, they really mean two wires, they just don’t count the ground return as a wire. No matter, I still think this is a great technology. So I was delighted to see that Dick Cappels had a great article in Circuit Cellar on implementing a one-wire system using an Atmel ATmega8515 microcontroller.


You can tell Dick Cappels is the real deal since he actually builds the one-wire circuit he describes in the article.

This is Dick’s vamp off the Maxim one-wire products that send power and communicate to a device over a single wire (not counting that return path). This was dreamed up by Dallas Semiconductor, before Maxim bought them in 2001. What I like about Dick’s solution, besides his using an Atmel MCU, is that for a couple of cheap parts, you can do one-wire communications with any peripheral made by anyone, as long as you go slow enough. He calls it analog communication, which I also love.

This does not send a lot of power along with the bits; in fact, you don’t have to send any power if you don’t want to, but you should be able to scale things as needed. It is a subject near to my heart, since I dreamed up a system a few years ago to send power to a motorcycle headlight and communicate to the switches and gauges all over one wire. I will check out Cappel’s design, since we can all learn from each other.

Now a word about Circuit Cellar. You can read that blog post I linked to above, but the article itself is behind a paywall. I can attest, Circuit Cellar is worth every dime if you are a system engineer that is interest in hardware, firmware, and even mechanical hacks. It’s a little on the hobby side, but nobody will do your engineering job for you for 30 or 40 bucks a year.

I mentioned a Circuit Cellar article on a homebuilt DNA sequencer a while back—and I say it again, subscribe and pay the bucks for this great magazine. I thing they have a money-back deal, and best of all, for 230 bucks or so you can get all the old issues on a memory stick, and then add your pdf issues to that stick. Do be aware that it costs extra to get both print and pdf versions.