Electromagnetic Compliance Protection (EE TIP #115)

Electromagnetic compatibility (EMC) compliance is one of the last processes before a device may be released to the public. EMC goes hand-in-hand with electromagnetic immunity (EMI), but immunity is only needed for critical devices. With EMC, it is very important to find a good EMC company to deal with. With most circuits, the weak point for EMC is any external leads. By adding a few inexpensive parts, EMC protection can be added and the EMC filtering can be adjusted by changing the values of the parts. In the figure below, the 1 µH inductors act as chokes to block any external voltage spikes above a certain frequency. The 1 nF capacitor also acts as a shock absorber to reduce any sharp voltage spikes. Effectively, this is a second-order filter and the cutoff frequency may be reduced by increasing the inductance and capacitance.

EMC ProtectionEditor’s Note: This EE Tip was written by Fergus Dixon of Sydney, Australia. Dixon, who has written two articles and an essay for Circuit Cellar, runs Electronic System Design, a website set up to promote easy to use and inexpensive development kits. Click here to read his essay “The Future of Open-Source Hardware for Medical Devices.”

The Future of Open-Source Hardware for Medical Devices

Medical technology is changing at a rapid pace, but regulatory compliance is also becoming increasingly harder. Regulatory compliance can act as a barrier to innovation, but it is a necessary check to ensure quality medical care. For small companies, aligning innovation with regulatory compliance can only help.

Fergus Dixon

When designing any new product, the FDA-recommended process is a great reference. First, the design input requirements must be written down. After the device has been designed and prototyped, verification and validation (V&V) will ensure that the device meets the design input. The device is then documented, creating the design output or device master record (DMR). Each device made is checked against the DMR and documented in the device history record (DHR). So all the details on how to make the device are contained in the DMR, and the results and traceability are recorded in the DHR.

My company recently asked an overseas company to design and manufacture an existing product. After many e-mails, the overseas company managed to build a working unit and immediately requested an order for 1,000. Before ordering even one unit, there was the matter of V&V. So what is V&V? Verification is the act of ensuring that the circuit acts as it should, as the circuit designer intended. This involves testing to a predetermined criteria, where the pass/fail is clearly defined. Testing happens by varying the inputs and checking the outputs to test the device as close to 100% as reasonably possible. When the inputs fall outside a normal range (e.g., a 10-VDC instead of 12-VDC battery voltage), the device must still work or it must provide a message showing why the device will not work (e.g., low battery light). Validation is the act of ensuring the circuit works as the customer or patient requires. This involves field testing, feedback, and rework—lots of it.

Working for medical device companies can be very rewarding. Smaller companies tend to work at the cutting edge. Larger companies are more secure and have stable products, but they can be less agile. With one company, we had a device that used smart batteries. During testing, we discovered that the batteries would not charge below 15ºC. After many meetings and e-mails to the manufacturers, the problem went to management, who decided to change the manual to say: “Do not charge below 15ºC.” Smaller dynamic companies can attract the best scientists, which is great until a connector fails and there is a roomful of highly intelligent people with no soldering iron experience. Every technology company can benefit from having at least one experienced technician or engineer. A few hours spent playing with an Arduino is a great way to get this experience.

What about open-source hardware (OSHW) for medical devices? For home hobbyists and students, OSHW is great. There is free access to working circuits, programs, and sketches. C compilers, which once cost several thousand dollars, are mostly free. For the manufacturers, the benefits are plenty of feedback, which can be used to improve products. There is one roadblock, and that involves the loss of intellectual property (IP), which means anyone can copy the hardware. Creative Commons has addressed this with an agreement that any copies must reference the original work. Closed-source hardware can also be good and present fewer issues with losing IP. Apple is a great example. Rather than use feedback to improve products, it makes smart decisions about future products. The iOS vs. Android battle can be viewed as a closed-source vs. open-source struggle that still hasn’t produced a winner. Medical devices and OSHW will have to meet up sometime.

Fergus Dixon’s embedded DNA sequencer project (Source: F. Dixon)

What about the future of medical devices? Well, the best is yet to come with brighter organic light-emitting diode (OLED) displays, a multitude of wireless connectivity options (all using the serial interface), and 32-bit ARM cores. DNA is gradually being unlocked with even “junk DNA” becoming meaningful. The latest hot topics of 3-D printing and unmanned aerial vehicles (UAVs) have direct medical applications with 3-D printed prosthetic ears and medical nanorobotics ready to benefit from UAV technology. Using a new sensor (e.g., a gyroscope) now means visiting an online seller such as Pololu, which offers ready-built development kits at reasonable prices. A recent design was a manually assisted CPR device project, which was abandoned due to lack of funding. How great would it be to have a device that could not only improve the current 10% survival rate with CPR (5% without CPR) but also could measure a patient’s health to determine whether CPR was helping and, even more importantly, when to stop administering it? Now that would be a good OSHW project.