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I Grew Up in the 80s & Survived!

[Editor’s note: Another ADI look into the world of electronics mystery from the series “Rarely Asked Questions: Strange but True Stories From the Call Logs of Analog Devices” guest authored by Gustavo Castro, an application engineer.]

Q: What should concern me when testing my heart-rate monitor prototype?

A: Recently I came across a humorous video on YouTube. “I can’t believe we made it” showed many activities that were common when I was a kid, but are considered dangerous by today’s standards. While it may seem downright irresponsible to let children get involved in most of these activities (some would actually get us in trouble with the law), it was not a big deal back then. But because some people got hurt, sick, or worse, we have learned to be more careful. The video made me reflect on activities we do today, and how we will someday look back and think, “How did we ever do that?”

Fortunately, electrical engineering has become less dangerous than it used to be (±300-V supply voltages for op amps like the K2-W are no longer necessary). Yet, we still find ourselves in situations where we are walking into unsafe territory.

During my days as an electrical engineering student in the late 90s, we had to choose a capstone project. Interest in biomedical instrumentation was growing, so my team and I decided to design a portable ECG. The goal was to diagnose difficult to detect arrhythmias by monitoring heart rate. Back then, we understood that isolation was necessary for a final product, but never really stopped to think too much about the development stages. Neither did we understand that test equipment may or may not be isolated, or even the type of isolation that may have been used.

We quickly identified that acquiring the signal was the most important first step, so we got an AD620 instrumentation amplifier and a few op amps for filtering and right-leg drive. To achieve isolation, we applied power through a 9 V battery and used a DC-to-DC converter to generate the ±15 V supplies. We purchased some silver/silver-chloride electrodes, and twisted the wires between the electrodes and the breadboard to avoid noise pickup. So far, so good. Now, a test subject had to open his shirt, stick the electrodes on, and… Oh yes, we needed to observe what came out the other end, so we probed the output with an oscilloscope.

The thing about oscilloscopes is that their ground is supposed to be connected to earth ground. So, they ground the system, thereby violating the isolation requirement. We were now exposing ourselves to become conductors of leakage currents. What was worse, these could flow right across our chest. And, because nothing ever works the first time, we were probing with the scope and a bench DMM at the same time, all while having someone connected to the electrodes. If you know a thing or two about leakage currents on isolated supplies, you might be wondering, “How is this guy still alive?”

Fast-forward 15 years. Today, thanks to increased health awareness and wearable computing devices, heart rate monitoring is going mainstream. This has increased the number of people experimenting with heart rate monitors, such as the AD8232, or looking into newer alternatives for high-quality ECG recording with AD620 successors like the AD8421 and AD8422.

This has also increased the number of unsuspecting engineers that may be putting themselves at risk. I like to remind my fellow EEs to be careful, and to make sure that they understand, and follow, safety guidelines before testing prototypes on live subjects. For this purpose, several resources are available in print and on the web. If you have any doubts, commercial ECG signal generators can be purchased at relatively low prices, increasing your chances of surviving the 2010s!

References:

— Gustavo Castro () is an applications engineer in the Linear Products Group in Wilmington, Mass. His main interests are analog and mixed-signal design for precision signal conditioning and electronic instrumentation. Prior to joining Analog Devices in 2011, he worked for 10 years designing high-performance digital multimeters and precision DC sources at National Instruments. Gustavo received a Bachelor’s degree in electronics engineering in 2000 from Tecnológico de Monterrey, Mexico. He holds three patents.

16 comments on “I Grew Up in the 80s & Survived!

  1. samicksha
    September 30, 2014

    Thank You Steve, you reminded of those fun days, me and my team agreed on Voltage Doubler Circuit wherein circuit helps to convert 12V DC current to 24V DC current. Although it is common now but i remember how much rework we did to complete and present this project.

  2. bjcoppa
    September 30, 2014

    As noted in this interesting article, wearable devices are beginning to take off. Of course, most people did not expect smartphones and mobile computing to be such a big hit 10 yrs ago. Look where we are now as desktop and laptops are being phased out in many companies and homes. Marketing in tech companies needs to focus more on the crystal ball of forecasting rather than merely focusing on the getting the business from the next client in the room

  3. bjcoppa
    September 30, 2014

    Newest iPhone has heart rate monitoring capability. Polar is a leader in health, fitness wearable device monitoring and sold tech to leading mobile device makers for integration and apps

  4. goafrit2
    October 1, 2014

    >> Of course, most people did not expect smartphones and mobile computing to be such a big hit 10 yrs ago.

    I have come to agree on one thing – the hardest part is not the technical aspect but forecasting and understanding what the customers want. Go to any developing country today, everyone has a smartphone. The old Nokia feature phones are gone. I mean, I never expected that. It is unbeliavable how everyone struggled to predict the tech ecosystem,

  5. goafrit2
    October 1, 2014

    >> This has increased the number of people experimenting with heart rate monitors, such as the  or looking into newer alternatives for high-quality ECG recording with AD620 successors like the  and .

    I predict within a decade, we will have all these sub-systems as a pure SOC. ECG, EMG, EOG and NR are all primitive systems now. They need to improve in terms of noise suppression and SNR. I know ADI and other firms are pushing hard in these areas but when you check the benchmarks, we have not advanced this fast enough in the industry. They are still bulky and energy dissipating.

  6. fasmicro
    October 1, 2014

    Marketing in tech companies needs to focus more on the crystal ball of forecasting rather than merely focusing on the getting the business from the next client in the room

    If you focus on forecasting, you may become a consultant. Just knowing what the future will be does not mean without the right product that you can take advantage of the opportunity. You still need to solve the technical problem irrespective of what you see about the future.

  7. cookiejar
    October 2, 2014

    I have suffered from heart arrhythmia for over 15 years now.  During that time my cardiologists have had me wear a holter (portable battery operated ECGs) for periods of 24 hours to 7 days at least 3 or 4 times each year.  Typically I'm issued a different model each time.

    Many times I noticed that my arrhythmia increased significantly when wearing these devices, which I attribute to leakage currents, which are rather well connected to one's heart.  The medical “technicians” of course deny that there could possibly be any problem as the devices were powered by a mere 3 volt battery.

    One particular holter sticks in mind, as I was bothered by arrhythmia as soon as it was connected.  Once at home,  I noticed the input connector was right beside the battery door. When I opened the battery door, I was appalled to see a growth of green corrosion between the battery terminals and the electrode input connector which were very close to each other.  I disconnected the electrode connector to immediate relief and carefully cleaned up the mess with alcohol and a Q tip.  Upon reconnection,  my heart beat stayed normal for the rest of the 7 day test period.

    When you think of it, the environment of these devices is quite harsh, typically being worn under one's clothes, subject to very high humidity and salty sweat.  I've yet to see one that used conformal coating on the PCB in order to minimize leakage effects – I routinely look inside the battery door to check. 

    Come to think of it, the regulations concerning medical devices have been far more slack than any other electronic devices.   EMI requirements for medical devices have been virtually non-existent for years.    Compliance Engineering magazine's reference guides document many truly frightening case studies of medical devices causing fatalities because of EMI.  I have a friend who worked as a hospital electronics technician who denied there were any unusual problems.  When we went down the list of case studies, he was surprised that he had in fact come across every one of those problems but didn't realize they were caused by EMI.  It was a real eye opener for him. 

    One would think that regulations concerning life and death electronic instrumentation would be far stricter.

  8. BBlitz
    October 2, 2014

    < >

    That's because no matter what any sales droid tells you, conformal coating does affect the circuitry.  With ECG it's a very high impedance and you're amplifying the heck out of it.  I've worked for several heart monitoring device companies and we tried numerous brands of conformal coating and never had any success.  Most would render the pulse detection circuit completely dead.  We ended up having to improve the sealing on the cases, but the input ports and battery doors were always an issue, especially when they came back in from service and had to be cleaned and returned to use.  Most users, and even the technicians trained to service them, over clean them with a wet cloth and some ineviteably finds it's way inside…along with lots of other gunk you don't even want to know about.  The turn around time is mere minutes to process one…and unfortunately has to be due to minimal reimbursement from the insurance/government programs.

  9. goafrit2
    October 2, 2014

    >> One would think that regulations concerning life and death electronic instrumentation would be far stricter.

    I think they do try. The problem is that human system is so convuluted and unique that there are always issues. It makes it increasingly difficult but that does not mean we cannot get it. I know the complaint is always how strick the FDA is. But being strict does not mean being right as they still do miss the important things that matter to keep patient alive.

  10. cookiejar
    October 4, 2014

    I am actually quite horrified with the attitude of the person in the holter industry who commented that they didn't have any luck with conformal coatings and that gunk seemed to regularly get into the devices.

    We are not talking about an entertainment device here, but a medical device that can cause serious harm and even death.  Of course the usual cop-out for defective medical electronics applies – the person was sick with a heart condition … – deaths are not unexpected.

    I was involved with a troublesome conformal coating issue some years back.  We tested 15 conformal coatings, before we found one that was satisfactory.  Besides the requirement of proper cleaning of the board, there was the issue of outdated chemicals, with no 'best before date” with some already turned into gel.  You just have to keep at it and bug the manufacturers.  In the end we did achieve results of no measurable leakage while submerged in a salt bath at 50C for 4 weeks.
     
    Connectors for the electrodes are another issue, easily solved as economical water tight connectors are now very common.

    The matter of the case sealing is another issue of sloppy engineering.  The cases used are custom built.  Simply get a manufacturer who has experience making water tight cases.

    I cannot believe that I have to advocate for due diligence in electronic design for the environment in which they are used and push for the concept of doing no harm.  
    One of the lives you save may be your very own.

  11. cookiejar
    October 4, 2014

    “One would think that regulations concerning life and death electronic instrumentation would be far stricter.”

    Perhaps the problem is psychological.  Talented, experienced and conscientious engineers don't go into the medical electronics field because they realize all that can go wrong with their designs and they don't want to feel responsible for killing someone – PTSD and all.  So the medical field is full of the opposite kind of engineers and medical practitioners.


    Did you ever notice the legal notices in all semiconductor data sheets stating that the product is not to be used in medical equipment relied on to sustain life?  Where are those semiconductors supposed to come from – the counterfeit market?

  12. BBlitz
    October 6, 2014

    Wow, you read far too much into things and make some pretty ridiculous assumptions.  There are many bright and talented people in the industry trying to make a difference and help society as a whole, but government policy & regulation and legal issues tend to hinder progress.

    Also, if you had fully read the datasheet, you'd know those statements are there to satisfy the lawyers (the real problem with the medical engineering field).  One simply needs to contact the manufacturer and discuss the intended use/application and sign an agreement limiting liability.  The parts are usually one and the same, sometimes with additional testing…but typically not.

  13. fasmicro
    October 7, 2014

    >> Did you ever notice the legal notices in all semiconductor data sheets stating that the product is not to be used in medical equipment relied on to sustain life? 

    That is a great observation. Yet from my experience you can ask the OEM to make components specifically for medical product application. What they are saying is that you cannot just go to the open market and buy something and hope to use same in the product. That will be an issue and they want none of the risks.

  14. fasmicro
    October 7, 2014

    >> The parts are usually one and the same, sometimes with additional testing…but typically not.

    Most times they are not. It is very likely the medical ones are better designed with many failure-protections and they cost so much. I have been involved in making a gyro for medical and consumer market. While the consumer one goes for 60 cents, the medical one is around $160. In the latter, they are totally re-engineered.

  15. BBlitz
    October 7, 2014

    >> Most times they are not. It is very likely the medical ones are better designed with many failure-protections and they cost so much. I have been involved in making a gyro for medical and consumer market. While the consumer one goes for 60 cents, the medical one is around $160. In the latter, they are totally re-engineered.

    That is sometimes true for specialized sensors or assemblies, but for the bulk of the electronic components (actives and passives) that I was referring to, they are identical.  The level of testing, and the cost is the same as any other industry, with the exception of implantables…and the main cost drivers there are enhanced traceability and testing (and additional padding for liability of course).  Personally, I believe more thought and effort goes into automotive grade components.

  16. samicksha
    October 14, 2014

    I guess there are number of application around in IOS and Anroid to support health related measurements but i am not sure how accurate they are, i have tried one of them which helped me to measure Blood Pressure but didn't found that of much help.

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