The iPhone Sensors

In addition to the touchscreen, your iPhone contains either five or seven important sensors depending on the model. Both the iPhone 3GS and iPhone 4 contain a proximity sensor, an ambient light sensor, a tilt sensor (also known as an accelerometer), a digital compass, and a Global Positioning System (GPS) receiver. The iPhone 4 also adds a built-in three-axis gyroscope and a noise-cancellation microphone to the array of sensors. These sensors give your iPhone some science-fiction-grade features that set it apart from the crowd.


Proximity Sensor
The proximity sensor is located on your iPhone right near the earpiece. Its job is to blank the screen when the iPhone is held up to your ear. This means your ear and chin won�t accidentally hang up your calls with their stray touches, and it means you�ll save some power during those phone calls.

You can see the proximity sensor in action by going to Phone ? Voicemail. Set Speaker to off (on is a brighter blue; off a dimmer blue), and then play a voicemail message by tapping the name or phone number of the person who left it. With the speaker off, place a finger just above the earpiece. The iPhone display goes dark. Remove the finger, and the screen returns.

Test the sensor range by placing your iPhone on a flat surface and holding your finger in the air about an inch above the earpiece. Move the finger up and down slightly, and you�ll discover exactly where the sensor gets triggered. The proximity sensor works by shooting out an infrared (IR) beam, which is reflected back and picked up by the iPhone�s light sensor. If the range is short enough, the iPhone switches off the screen.

You can also see the IR source for the proximity sensor by using a digital camera. The IR beam is visible to the camera�s CCD detector. To take the picture we switched off a camera�s flash, enabled its Macro settings (because we needed the camera to be pretty close to the iPhone), and waited for the source to flash red. You can�t see it with your eyes, but you can with your camera�s IR-sensitive detectors.


Tilt Sensor
The iPhone uses an accelerometer (what we�re going to call the tilt sensor) to detect when your iPhone tilts. Many apps, including Safari, update their displays when you turn the iPhone on its side. This allows you to use your iPhone in both portrait and landscape modes.

If you feel like playing with the tilt sensor, try this: go into Photos, and select a favorite picture. Hold the iPhone up normally in portrait orientation, press one finger onto the screen, and then tilt the phone into landscape orientation. The picture will not change. Now, lift the finger off the screen. Presto�the iPhone finally rotates the display.

Many iPhone games use the accelerometer for user interaction. For example, with the very popular Flick Fishing game, you �cast� a line out to catch fish by moving your hand and arm in the motion of casting. Many driving games let you use your iPhone as a steering wheel as your drive along a virtual course.


Ambient Light Sensor
The ambient light sensor detects whether you�re in bright or dark lighting conditions and then adjusts the overall brightness of your iPhone display to match. For example, if it�s extremely bright outside and you pull out your iPhone to make a call, the light sensor will judge the surrounding brightness when you unlock the phone and let the iPhone know that it needs to compensate by making the display brighter so you can read it. Going the other way, the screen will dim when you�re in a dark room to protect your eyes from the glare of a bright screen as well as save some battery power.

Want to have fun with this sensor? When you cover the sensor (found just above the ear speaker on the top front of the phone) with a finger and then unlock the phone, you�ll find that the screen brightness is quite dim. On the other hand, if you shine a bright light at the sensor when you unlock the iPhone, you�ll see the screen at a very bright setting.

You can toggle the auto brightness feature off and on in Settings ? Brightness. This setting also offers direct control over the brightness of the iPhone�s screen, which is handy when you need immediate results instead of playing with bright lights, fingers, and unlocking your iPhone.


Digital Compass
The digital compass (also known as a magnetometer) built into the iPhone 3GS and iPhone 4 is similar to a magnetic compass. In other words, if you happen to be near a strong magnetic field such as the magnets contained in the iPhone earbuds, the compass needle may not be pointing toward true or magnetic north. On occasion, the digital compass may need recalibrating.

The iPhone Compass app will inform you of those rare occasions by displaying a message that says �Re-calibrate compass. Wave in a figure 8 motion.� That�s your cue to hold the iPhone out in front of you and draw a big figure eight, with the eight lying on its side. Keep moving the iPhone until the calibration message disappears. Yes, you will look like a total geek while doing this, but it�s better than getting lost, right?

If you�re in a car and driving around, you don�t need to wave the iPhone at the windshield. Just make a few turns, and the compass will recalibrate itself. That�s much safer for everyone in and outside of your car.


GPS Receiver
Not only is your iPhone 3GS or iPhone 4 an amazing, powerful pocket computer and a very capable phone, but it�s also a state-of-the-art navigation tool. Built inside the latest iPhones is a GPS receiver that is capable of pinpointing your exact location on the globe within about 30 feet (10 meters).

In fact, your iPhone has an advantage that many dedicated GPS receivers do not. Since it is constantly in touch with cell phone towers with precisely known locations, it can determine your approximate location within several seconds of being turned on. Once the iPhone has locked onto several GPS satellites, it pinpoints the location with even more accuracy. This capability of blending the GPS satellite signals and known cell tower locations is known as Assisted GPS (A-GPS).

The GPS receiver is used in most iPhone apps that contain some sort of geolocation feature. Some examples of these apps include Maps, the Navigon, Tom Tom, and AT&T navigation apps, and the official Geocaching (www.geocaching.com) app.

NOTE: The Global Positioning System consists of a constellation of 24 to 32 satellites in precisely known orbits about 12,550 miles above the earth�s surface, all equipped with extremely accurate clocks and powerful radio transmitters. GPS receivers determine their location by timing the reception of signals from four or more satellites and then performing a series of complex calculations.


Three-Axis Gyroscope
The iPhone 4 is the first mobile phone to contain a miniaturized three-axis gyroscope to determine the precise orientation of the phone at every moment. This is handy in gaming apps that may need to track the motion of the phone more accurately than the tilt sensors can and also in apps such as You Gotta See This! (www.boinx.com/seethis). The latter is an iPhone 4�specific app that creates photo collages simply by waving the phone around in front of you. The iPhone shoots photos as it is moving, and since the app knows the orientation of the iPhone�s camera as each photo is being taken, it can easily stitch them into an attractive collage in seconds.

The gyroscope can be used by iPhone developers to capture movement that isn�t sensed by the accelerometer. Although the accelerometer does a good job of detecting whether the iPhone has been tilted one way or another, the gyroscope allows the device to be moved left or right, up and down, or forward and back, and that motion can be understood by apps. These additional movements provide another layer of precise control to the gestures that the iPhone understands.


Noise Cancellation Microphone
A glance at the top of an iPhone 4 will show a tiny hole next to the headset jack. This hole is actually a microphone, given the name top microphone by Apple. What�s it used for? It�s for improving the quality of your voice phone calls.

The Noise Cancellation microphone samples the ambient noise level around you. It then subtracts much of that ambient noise from the signal being sent to the person on the receiving end of your phone call. The result is much more clarity when you�re making phone calls in noisy conditions.

Source of Information : Taking Your iPhone 4 to the Max