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Bench Talk for Design Engineers

Bench Talk

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Bench Talk for Design Engineers | The Official Blog of Mouser Electronics


Selfie with a Shark Lynnette Reese


 


A television commercial for the Samsung Galaxy 7 Edge encourages us to think our cell phones are indestructible. In the midst of a selfie, a young girl drops her phone into a shallow fountain. There is no damage: She picks the phone from the water, shakes it off, and goes back to composing her picture. Lest there be any doubt, a voiceover tells us the S7 carries an IP68 rating — good for 30 minutes in five feet of water.


For a good while now we’ve thought of our phones as fairly drop proof (how many times have you dropped yours?), relying on the solder joints to keep the semiconductor components tightly mounted to their circuit cards. Before flash memory became widely available and cheap, (enabling smartphones enough storage space for personal data, music videos and pictures) cell phone manufacturers like Nokia wrestled with the possibility of using micro-miniature disk drives. Too fragile for smartphones or portable media players, smartphone makers concluded, too many moving parts, a strong possibility for damage if the phone were dropped, and an almost universal assumption that, many times during its life time, the phone would be dropped.


Thus, the smartphone makers assure us it is not just the builders of the Industrial Internet of Things (IIoT) who are concerned with ruggedness and the ability to function well in harsh environments. With the proliferation of remote sensor networks, designers routinely make judgments on the ability of the components to function under environmental stress. With smart city environments, as one example, smart traffic lights are supposed to regulate the speed of trucks, buses and passenger vehicles. They are expected to clear roadways for emergency vehicles or snow plows. Suspended on telephone poles and lamp posts, smart traffic sensors must exercise precision under elevated temperature and humidity and the same sort of precision must be available in blizzards and hurricanes. I personally believe that the truly “smart” traffic lights are the ones that wait until you are just about to enter the intersection to turn yellow and then quickly red so they can catch a departing image to boost traffic enforcement revenue.


Consumer products may not be advertised to perform perfectly in blizzards or hurricanes. But they do need to be specified, and thus work, in the outdoor environments where people often use them. There are tablets and large-screen PDAs used on construction sites, for instance, in environments with a great deal of dust. Some smartphones are specifically sealed as to offer resistance to seawater, in case you plan to text your girlfriend while on the next Navy Seal rescue operation or want to take a selfie with a shark.


The MIL-STD-810G military specification specifies 19 categories under which electronic equipment — even consumer goods — can be specified for applications operating under harsh conditions, including expectations for water and moisture resistance, dust and particulate resistance, shock and vibration resistance, and durability. High temperature environments also apply. In case you are wondering, there are five categories specified for underwater resistance alone:


·      Blowing rain

·      Immersion

·      Raindrops (as if blowing rain isn’t bad enough)

·      Low-pressure atmospherics

and

·      Durability in saltwater.


Shock resistance includes the ability of an electronic device to survive drops, shocks (abrupt slams and jerks), and prolonged vibrations. I know that two year olds are great for testing products in this very area. (Toys and military products probably differ mainly in color. Camo etch-and-sketch, anyone?)


OK, let’s get serious: these are not arcane specifications for equipment in paint factories or on welding robots. They apply to smartphones, smart watches, and other wearables. The Samsung Galaxy S7 Edge is “Ingress Protected” IP68- rated, so it can survive being in more than 4 feet of water or up to 30 minutes in water and is dust resistant. This includes the USB charging port. You can’t go swimming with this in your pocket, but if your phone is outside while you are and a huge rain storm hits, your phone will not die. That happened to me about a year ago. I set my phone down while helping with an outdoor installation (of a rain gauge) and suddenly a rain storm hit. We all ran into the utility shed and I realized I had left my phone on a post. I ran back and got it within 2 minutes or so, but it was too late. Those raindrops cost me about $600. How many people have dropped their phone in a toilet or in the pool? I won’t ask for a show of hands, but we know that everyone of us has lost electronics to water in some form or another. Not anymore. I don’t recommend a selfie with a shark, however. IP-68 doesn’t say anything about sharks.



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Lynnette Reese holds a B.S.E.E from Louisiana State University in Baton Rouge. Lynnette has worked at Mouser Electronics, Texas Instruments, Freescale (now NXP), and Cypress Semiconductor. Lynnette has three kids and occasionally runs benign experiments on them. She is currently saving for the kids’ college and eventual therapy once they find out that cauliflower isn’t a rare albino broccoli (and other white lies.)


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