Physics Toolbox
by Vieyra Software
Sensor & Generator Info
Scroll down this page to learn about each of the sensors in your phone. Some Physics Toolbox app modes use more than one sensor. Look for the green text to identify which app modes use each sensor.
G-Force Meter (Inertial Sensor)
Modes that use this sensor
g-Force Meter
Linear Accelerometer
Roller Coaster
Inclinometer
Description
The g-force meter measures the ratio of normal force to gravitational force (FN/Fg) in three dimensions. The g-force changes whenever the mobile device accelerates: speeds up, slows down, or changes direction. When the mobile device is not accelerating and lying face-up with respect to the surface of the earth, it reads g-force values of 0, 0, 1. This means that a normal force is only experienced in the upward direction, and that it is in equal strength as the force of gravity. An object that experiences a vertical g-force of 2 feels a force twice as strong as that of gravity in the upward direction (which is interpreted as “feeling twice as heavy”). An object that experiences a g-force of 0 is in free-fall (which is interpreted as “feeling weightless”).
Operating Principle
G-force data is extracted directly from the accelerometer. Accelerometers often come in two flavors: piezoresistive cantilevers and capacitative. Piezoresistive cantilevers are protrusions of silicon, sometimes crafted with a paddle at the end that serves as an inertial mass. As the mobile device accelerates, the cantilever bends, changing the resistance of the silicon, which is interpreted as acceleration. Alternatively, a capacitive accelerometer contains three inertial comb-like masses attached to springs, with one in each dimension. When the mobile device is not accelerating and lying flat, a total g-force of 1 is measured due to the downward-pulling gravitational force (and the resulting upward reaction force of equal strength). When the mobile device accelerates, one or more inertial masses along the directions of acceleration move around in the presence of capacitor plates between the comb-like masses, varying the electric potential across the plates. Change in the electric potential across the plates is interpreted as acceleration and a change in g-force.
Additional Resources
How a Smartphone Knows Up from Down
Bosch Acceleration Sensor Technical Specifications
Linear Accelerometer (Inertial Sensor + Data Manipulation)
Modes that use this sensor
g-Force Meter
Linear Accelerometer
Roller Coaster
Description
The linear accelerometer measures acceleration in a straight line in three different dimensions. Linear acceleration changes whenever the mobile device speeds up, slows down, or changes direction. When the mobile device is at rest with respect to the surface of the earth, it reads acceleration values of 0, 0, 0. Linear acceleration differs from general acceleration. This is because engineers commonly interpret the displacement of the inertial mass in the z-direction as the relativistic acceleration of an object on the surface of a rotating earth. This is accurate when one considers the whole earth as the frame of reference, but is not accurate when considering a local frame of reference.
Operating Principle
Linear acceleration is derived from the g-force meter, but also uses the gyroscope and the magnetometer to negate the effects of the earth’s gravitational field on the sensor. The accelerometer contains either a cantilever or comb-like inertial masses attached to springs, with one in each dimension. (See g-Force Meter, Gyroscope, and Magnetometer information).
Additional Resources
How a Smartphone Knows Up from Down
Bosch Acceleration Sensor Technical Specifications
Gyroscope (Inertial Sensor)
Modes that use this sensor
Linear Accelerometer
Gyroscope
Roller Coaster
Compass
Inclinometer
Description
The gyroscope measures rotational velocity around three axes.
Operating Principle
The gyroscope is often composed of one or a paired set of comb-like inertial masses that are free to move along a plane. A small electrical current causes the frames of the comb-like structures to resonate along a single dimension. When the mobile device rotates, the comb-like structure begins to move out of the single direction of resonant vibration. This is due to the Coriolis effect, often attributed to the Coriolis force (a false force) that results from different frames of reference. As the mobile device spins, the comb-like mass moves about in the presence of capacitor plates between the comb-like structures, varying the electric potential across the plates. The changes in electric potential due to the difference in direction of the vibration compared to a non-rotating system is interpreted as a rotational velocity.
Additional Resources
Working Principle of a Gyroscope
How MEMS Accelerometer, Gyroscope, Magnetometer Work
Barometer
Modes that use this sensor
Barometer
Roller Coaster
Description
The barometer measures the ambient pressure of the mobile device.
Operating Principle
The barometer contains a small cavity filled with gas that is entirely enclosed. The top side of the cavity is covered with a membrane that has a network of resistors embedded within it. As the pressure increases or decreases, the membrane changes shape. As a result of the change in shape, the resistors in the membrane undergo changes in crystal structure, which then changes their resistivity. Changes in the resistance across the membrane are interpreted as changes in atmospheric pressure.
Additional Resources
Working Principle of a Pressure Sensor
Roller Coaster (Combination Sensor)
Modes that use this sensor
Roller Coaster
Description
The roller coaster tool is composed of series of sensors useful for roller coaster analysis, including the g-force meter, gyroscope, and barometer.
Operating Principle
(See g-Force meter, Gyroscope, and Barometer information).
Hygrometer (Integrated Environmental Unit Sensor)
Modes that use this sensor
Hygrometer (available on a very limited number of smartphones)
Description
The hygrometer measures the relative humidity in the air. This is measured as a percentage of water capacity for the air, based upon air temperature.
Operating Principle
The hygrometer includes a small chip with a membrane in the middle supported by one or more cantilevers that can measure strain. As water accumulates on the membrane, it becomes strained. Greater strain on the cantilever changes its resistance, which is interpreted as a change in relative humidity. This value is quantified with respect to the ambient temperature. (See Thermometer information).
Additional Resources
Bosch Integrated Environmental Unit Sensor Technical Specifications
Thermometer (Integrated Environmental Unit Sensor)
Modes that use this sensor
Thermometer (available on a very limited number of smartphones)
Description
The thermometer measures the ambient temperature.
Operating Principle
The thermometer is composed of multiple micro thermocouples embedded in a membrane. Thermocouples are made of two small pieces of metal wire of different material, connected at one or two different points called junctures. When a juncture experiences a change in heat, the electrical potential measured between the two metals also changes, and is interpreted as temperature.
Additional Resources
Bosch Integrated Environmental Unit Sensor Technical Specifications
Proximeter
Modes that use this sensor
Proximeter
Description
The proximeter detects the presence of an object within a few centimeters of distance from the sensor.
Operating Principle
The proximeter consists of two parts: an infrared light emitting diode, and an infrared-detecting photodiode. The infrared light emitting diode constantly sends out light that is invisible to the human eye. When an object approaches the sensor, these light waves are reflected back toward the mobile device and absorbed by the infrared-detecting photodiode. The presence or absence of the reflected infrared light is interpreted as an object present or not present near the sensor.
Additional Resources
Photodiode Theory of Operation
Ruler
Modes that use this sensor
Ruler
Description
The ruler tool measures the vertical distance between two points of contact on the screen.
Operating Principle
Smartphones use capacitive touch screens to identify the points of contact of a conductive finger, stylus, or other object. Screens are manufactured with an electrostatic grid made of up very thin lines of metal, that can store excess electrons. Electrodes apply a low voltage to the grid. Any conductive object that comes very close to or touches the screen slightly distorts the electric field. The drops in voltage are measured, and the location of these drops are interpreted as a point of touch.
Additional Resources
Magnetometer
Modes that use this sensor
Magnetometer
Compass
Description
The magnetometer measures the magnetic field in three dimensions, and can also be used to measure the total magnetic field.
Operating Principle
Most magnetometers use either the Hall effect or the magneto-resistive effect. Magnetometers that use the Hall effect are composed of a flat conductive plate in each dimension through which flows an electric current. The presence of an external magnetic field causes the electrons to deviate from their straight path to a curved path, polarizing the plate perpendicular to the flow of electrons. This polarization can be measured as a difference in potential across the sides of the plate. A greater potential difference across the sides of the plate is interpreted as an increase in magnetic field strength in that given dimension. Magnetometers that use the magneto-resistive effect are composed to permanent magnets in a circuit. As the magnet is exposed to external magnetic fields, the resistance of the magnet in the circuit changes.
Additional Resources
How MEMS Accelerometer, Gyroscope, Magnetometer Work
Compass (Combination Sensor)
Modes that use this sensor
Compass
Description
The compass shows the direction of a total magnetic field by pointing in the direction of magnetic south (with no strong external magnetic field other than Earth’s geomagnetic field, this is typically interpreted as geographic north). The compass also provides a bubble level, which uses information from the g-force meter.
Operating Principle
The compass uses data from the magnetometer and points toward the strongest southern magnetic source. (See Magnetometer information).
Additional Resources
How MEMS Accelerometer, Gyroscope, Magnetometer Work
GPS
Modes that use this sensor
GPS
Description
The GPS sensor measures position (latitude, longitude, and altitude and, speed, and identifies the number of visible GPS satellites.
Operating Principle
The smartphone detects radio signals from satellites that carry a precise time stamp derived from an atomic clock. The smartphone receives the transmission by detecting the incoming radio waves using precise antennas that measure disturbances in the surrounding electromagnetic field by resonating at frequencies that match the GPS radio frequencies. By observing the time it took for the radio signal to arrive, it can determine its distance from the satellite using the known speed of light (with some corrections due to relativistic effects). This is done with at least four satellites for the phone to determine its position from multiple directions, allowing the smartphone to determine its x, y, and z (altitude) coordinates on the surface of the earth.
Additional Resources
How does your smartphone know your location?
Demonstrating GPS Trilateration
Inclinometer (Inertial Sensor)
Modes that use this sensor
Inclinometer
Description
The inclinometer measures the angle of the mobile device in the x, y, and z planes.
Operating Principle
The inclinometer uses data from the g-force meter while the mobile device is held at rest (see G-Force meter information). When the mobile device is held parallel to the x, y, or z plane, such as when it is held flat, all of the gravitational force is sensed in a single direction. When the phone is tilted out of the plane in any direction, the gravitational force now appears as components in each of the planes. These components are calculated using standard trigonometry to determine the angle at which the mobile device is held.
Additional Resources
How a Smartphone Knows Up from Down
Light Meter
Modes that use this sensor
Light Meter
Description
The light meter measures the intensity of ambient light in the visible range.
Operating Principle
The light meter is a photoresistor, composed of a semiconductor that only allows current to flow when the light waves hitting it have a precise band of frequencies. An IR and a UV filter are placed over the photoresistor, limiting the type of waves that can reach the semiconductor to be in the visible spectrum. As the number of light waves hitting the photoresistor increase, the current increases, and this is interpreted as an increase in light intensity.
Additional Resources
Color Detector
Modes that use this sensor
Color Detector
Description
The color detector asks the user to select a location on the screen, then interprets the color into both hex values and its common name.
Operating Principle
Mobile device color sensors, used for recording and reproducing images on the screen, use an array of colored filters over a plane filled with visible light-sensitive photodiodes. To detect individual colors of light, filters representing the primary colors of light (red, green, and blue) are placed over each photodiode, so that each photodiode only receives red, green, or blue light. The information received by these photodiodes can be organized and combined to determine the total combination color perceived by the human eye.
Additional Resources
Sound Meter (Microphone)
Modes that use this sensor
Sound Meter
Tone Detector
Oscilloscope
Spectrum Analyzer
Description
The sound meter records the intensity of sound.
Operating Principle
The sound meter sensor is composed of a capacitive microphone. The microphone is composed of a conductive membrane that flexes when it receives sound waves. A perforated solid conductive plate is placed behind the conductive membrane. When the flexible membrane moves in response to sound waves, the potential difference between the membrane and the back plate changes. These changes are interpreted as sound detection, with greater differences interpreted as higher intensity.
Additional Resources
Tone Detector (Microphone + Data Manipulation)
Modes that use this sensor
Tone Detector
Description
The tone detector uses the sound meter sensor to determine the strongest tone of a sound, and outputs both the numeric frequency of the tone and the letter representing its closest musical note.
Operating Principle
A sound sample is recorded for a brief period of time using the microphone (see Microphone sensor information), and a Fast Fourier Transform (FFT) analysis is applied to sound wave observed, which contains a wide spread of frequencies and amplitudes. The FFT breaks the sound wave observed into its component sine waves of various amplitudes and frequencies, and creates a histogram of the data. The most prominent frequency from the sound sample is displayed numerically.
Additional Resources
Fourier Transform, Fourier Series, and Frequency Spectrum
Oscilloscope (Microphone + Data Manipulation)
Modes that use this sensor
Oscilloscope
Description
The oscilloscope displays the sound wave representing an observed sound sample.
Operating Principle
A sound sample is recorded for a brief period of time using the microphone (see Microphone sensor information), and a Fast Fourier Transform (FFT) analysis is applied to sound wave observed, which contains a wide spread of frequencies and amplitudes. The FFT breaks the sound wave observed into its component sine waves of various amplitudes and frequencies, and creates a histogram of the data. The most prominent frequency from the sound sample is displayed numerically.
Additional Resources
Spectrum Analyzer (Microphone + Data Manipulation)
Modes that use this sensor
Spectrum Analyzer
Description
The audio spectrum analyzer uses the sound meter sensor to determine the amplitudes (measured in acoustical units) of the multiple frequencies that make up a sound. It outputs a graph of amplitude versus frequency, and numerically displays the frequency with the greatest amplitude.
Operating Principle
A sound sample is recorded for a brief period of time using the microphone (see Microphone sensor information). Using changes in potential recorded from the sound meter, the sound wave is re-interpreted in time and space and is displayed visually showing the amplitudes of each frequency recorded.
Additional Resources
Fourier Transform, Fourier Series, and Frequency Spectrum