Tech Talk #60 – Sep. 16, 2017
How does my phone do that?
Sure, your smartphone can count your steps, show you which way is north, and point out your location on a map, but how does it do that?
Your smartphone is a sleek slab of plastic, aluminum, and glass that’s packed with sensors. Here are some of the sensors in your phone and what they do.
Accelerometer. An accelerometer measures linear acceleration. Your smartphone accelerometer uses a piezoelectric effect sensor. Microscopic crystal structures in your phone become stressed when moved. These crystals create a voltage from the stress, and the accelerometer interprets the voltage to determine your phone’s velocity and orientation.
Gyroscope. A gyroscope uses Earth’s gravity to help determine your phone’s orientation. These aren’t the gyroscopes of science class, though. Your phone uses Micro-Electro-Mechanical Systems (MEMS) gyroscopes to measure angular rotational velocity.
Together, accelerometers and gyroscopes are used to figure out if your phone is vertical or horizontal or moving. These are the sensors used when your phone is counting your steps, rotating the display, and figuring out if and how fast you’re moving.
Magnetometer. A magnetometer provides an orientation in relation to the Earth’s magnetic field. As a result, your phone always knows which way is North so it can auto rotate your digital maps depending on your physical orientation. And speaking of maps…
Global Positioning System (GPS). The GPS receiver in your phone communicates with the 30 global positioning satellites in the GPS system. It calculates your position using data from at least three GPS satellites and the receiver. GPS doesn’t use any of your phone’s data, which is why you can still see your location when your phone has lost signal. GPS does use a lot of battery though, which is why you should turn it off if you’re running low on a charge.
GPS isn’t the only way your phone can work out where it is—the distance to cell towers can be used as a rough approximation. GPS units inside smartphones combine GPS signals with cell signal strength to get more accurate location readings.
Barometer. Your smartphone has a barometer to improve GPS elevation results because those results can be adversely affected by atmospheric pressure. You can get apps that use the barometer to display your current altitude.
Cell towers and signal strength
I stumbled across a couple of fun resources to share this week:
Antenna Search @ http://www.antennasearch.com/
On the antennasearch site, enter the city and state and find out where communications towers are and who owns them. The search interface gets a C- grade for usability, but the results are interesting. Well, to some people.
Open Signal @ https://opensignal.com/
Find out your cell phone carrier’s signal strength around Tehachapi or anywhere else. Based on data uploaded by users of the Open Signal app and not on the marketing department of any particular carrier.
GPS fun facts
Like much of modern technology, GPS is a US government invention.
During the 1960s and 70s, the US military needed a precise navigation system for bombers and submarines, but the cost of putting up a bunch of satellites just for GPS was considered too high at the time. The Cold War made the cost for a precise navigational system for the US nuclear triad acceptable to Congress. The first system was called Navstar, or Navigation System Using Timing and Ranging, and the first GPS satellites were launched between 1978 and 1985.
In 1983, Soviet jet fighters shot down Korean Airlines Flight 007 after straying into the USSR’s airspace. Afterward, President Ronald Reagan issued a directive making GPS freely available for civilian use as a common good. At first, the GPS signal available for civilian use wasn’t as accurate as the military GPS. In 1996, President Bill Clinton signed a policy directive to provide the same accuracy for both military and civilian use.
GPS is owned and operated by the United States government as a national resource. The Department of Defense runs the GPS system and is required by law to “maintain a Standard Positioning Service… that will be available on a continuous, worldwide basis,” and “develop measures to prevent hostile use of GPS and its augmentations without unduly disrupting or degrading civilian uses.”
You have to be brave to jump out of an airplane, but not as brave as leaving your house with less than a 25% charge on your phone.
Do you have a computer or technology question? Greg Cunningham has been providing Tehachapi with on-site PC and network services since 2007. Email Greg at email@example.com.