Demystifying Smartphone Sensors

The smartphone experience is only getting better as more and more sensors are used in our diminutive giants.

With the increasingly competitive fight for smartphone supremacy and the media frenzy surrounding it scaling new heights everyday, it is not surprising that consumers are gradually starting to take the technology for granted.

While everyone knows the resolution of their screen, or whether their phones are running the latest versions of their respective operating softwares, critical parts of the phone often forgotten are the hardworking sensors. In fact, we think they’re our smart devices’ unsung heroes.

This article’s our ode to to the elves of the smart devices universe.


Smartphone sensors, much like any other sensors we would come across, have the ability to take physical quantities and convert them into readable signals. These little midgets collate and provide a mindboggling amount of disparate information and provide that to the OS and Apps, that are then used, to provide an amazingly wholesome experience with our devices.

An average smartphone today has upwards of five built in sensors functioning at any given time. We’ll analyse a few of the most important ones:

1. Accelerometer:

Probably the first motion sensor to be integrated into phones, the accelerometer allows the phone to sense the direction in which it is being used. This information is then transmitted to the screen, which then changes direction to give us a more comfortable view.

The accelerometer works on the principle that if an object is allowed limited free movement in a specific space, and the space is then accelerated, the acceleration can be measured if we can by some means measure the distance by which the object moves.

Consider a small rubber ball suspended by a spring in a long container. Move the container upwards, and spring is elongated by a certain distance before it settles down. Measuring the distance by which the spring was elongated will give you a measure of how much you accelerated the container by.

The working of the accelerometer MEMS chip.

In your phone however, the ball and spring is replaced by flexible silicon, which bends on acceleration, with a base attached to the phone acting as the container. When the thin silicon strips move between capacitor plates placed around it, the change in charge causes a current, the magnitude of which can be measured to give us the direction in which the phone is being accelerated.

The accelerometer sensor is used not only to change between portrait and landscape views but also in a number of games and fitness apps. It is the accelerometer sensor that allows the smartphone to measure the number of steps you’ve taken or how long you’ve been walking.

2. Gyroscope:

A gyroscope allows a smartphone to measure and maintain orientation. Gyroscopic sensors can monitor and control device positions, orientation, direction, angular motion and rotation. Used in combination with an accelerometer, smartphones now measure movement along six axes, allowing unknowing consumers to enjoy applications such as driving games without the knowledge that these sensors are some of the most complex in the world.


The working of a gyroscope

Its working is very similar to that of the accelerometer and it also makes use of MEMS chips. Unlike a traditional gyroscope however, the MEMS gyroscope does not use a rotating disc to measure orientation. MEMS gyroscopes use the principle that a vibrating object tends to continue vibrating in the same plane as its support rotates. In the engineering literature, this type of device is also known as a Coriolis vibratory gyro because as the plane of oscillation is rotated, the response detected by the transducer results from the Coriolis term in its equation of motion.

3. Proximity sensors:
 Proximity sensors enable the smartphone screen to power down when you bring the phone close to your ear when taking a call. This not only prevents any unwanted input when the screen touches your ear, but also helps save battery.

The working of the proximity sensor.

The working of the proximity sensor.

In its working, the proximity sensor is much simpler than the previous two sensors we have examined. Usually located near the speaker of the phone, the sensor functions by emitting infrared rays and then checking for their reflection. If the IR rays are reflected within a certain distance, (generally about 2–5cm) the sensor is activated and it responds by turning off the screen.

4. Ambient Light Sensor:
 Ambient light sensors are primarily battery saving tools. The theory is that as it gets darker around us, the brightness of the phone screen required to make it comfortable to use also decreases. By decreasing the brightness of the screen whenever we move indoors or under shade, the smartphone saves battery.


Ambient light sensors use photodiodes to function. These repurposed LED’s create a current when exposed to light; brighter the light, the higher the current they produce. The current is then converted into a signal which indicates to the smartphone what brightness the screen should be operating at.

This sensor is normally located near the proximity sensor on the front face of the smartphone.

5. Camera Sensor:
 For years manufacturers have been misleading consumers by quoting a high number of megapixels in their camera, with unknowing consumers almost always taking the bait. One aspect of the camera which is often wrongly ignored is the camera sensor.

The camera sensor is what determines how much light is used to create an image. The sensor consists of millions of light-sensitive spots called photosites which are used to record information about what is seen through the lens. The two main types of image sensors used are the CMOS sensor and the CCD sensor.


A CCD sensor consists of a large number of small cells which act as analogue devices. When light strikes the chip it is held as a small electrical charge in each photo sensor. The charges are converted to voltage one pixel at a time as they are read from the chip. Additional circuitry in the camera converts the voltage into digital information.

As for the CMOS sensor, A CMOS imaging chip is a type of active pixel sensor made using the CMOS semiconductor process. Extra circuitry next to each photo sensor converts the light energy to a voltage. Additional circuitry on the chip may be included to convert the voltage to digital data.

One could infer from the above information that a larger sensor is synonymous with better photos, but this over simplifying an extremely complicated piece of technology. Sure, a larger sensor would help, but a large sensor without anything else wouldn’t. Good photo quality is the product of a balance of efficiency of sensor technology, lens quality, image sensor size and ultimately what you want to do with your photographs.

6. GPS:
 GPS or Global Positioning System, is one of the older pieces of technology to be integrated into smartphones. The system functions using an antenna placed in your smartphone, and thus locates your smartphone on the basis of the satellite interaction.


The working of GPS.

When the GPS of your phone is turned on, the GPS antenna sends out signals to various satellites. On establishing communication with about three satellites, the phone can give you a fairly precise estimate of your location.

A new introduction to GPS technology is something called A-GPS or Assisted — GPS. A non A-GPS device may take up to several minutes to locate the satellites nearest to it. A-GPS speeds up this process by giving the device access to satellite almanac data over the cellular network, so the GPS receiver can immediately know where all the satellites are.

The location of the antenna generally varies from smartphone to smartphone. In the iPhone, the antenna is placed on the lower back of the device.

7. Pressure Sensor:
 One of the latest sensors to be added to smartphones is the pressure sensor. Like the accelerometer and gyroscope, the pressure sensor works using an MEMS chip.

The working of the pressure sensing MEMS chip.

In this case, the chip consists primarily of a diaphragm which bends on application of pressure. The measurement of this bending allows the chip to measure the pressure and then transmit the required data to the phone.

Though a relatively new addition, this sensor is already seeing many applications in smartphones. Measuring pressure allows the phone to roughly calculate the height at which the user is present, which allows for more accurate GPS. Apart from this, the sensor is also seeing wide scale application in new apps.

Amazingly, MEMS makers are still looking to expand on these sensors, with humidity and temperature sensors also already in the works. As more of these sensors are integrated into phones, there is no doubt that the user experience will continue to improve and the devices will become more interactive.

I know it’s been a long read, but hopefully you’ll have learnt a lot more about the world’s current unsung heroes!

Originally published at Chip-Monks.