9 Different Sensors

Engineering Behind

How Lab in Your Pocket Works

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From Sensor

The sensor detects the surrounding parameters and sends analogue signals to the microcontroller, embedded in the 3D printed box.

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Through
Microcontroller

The microcontroller, playing the role as an agent, deciphers the signals received and constantly broadcasts the series of data with its Bluetooth module.

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To App Interface

As a mobile device is paired with the microcontroller via Bluetooth, the Lab in Your Pocket app displays the data comprehensive to user. Data could furthermore be saved and analyzed.

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Gas Sensor

It comprises temperature and pressure sensors. The sensors determine temperature and pressure from the elecrical output across a thermoresistor and a pressure-sensitive semi-conductor respectively in the circuit. This electrical output is converted into its corresponding temperature and pressure by the microocontroller.

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Current Sensor

It is straightforward for the microcontroller to read the analogue signals from the current sensor. The higher the current flowing through, the stronger is the signal received. It possesses very low internal resistance such that it does not divert much current from a series circuit.

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Hall Sensor

Like a traditional search coil used in physics laboratory, the Hall sensor encompasses a tiny "search coil" within which current would be induced when perpendicular magnetic field passes through it. The microcontroller takes one step further and convert this current into magnetic field strength.

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Voltage Sensor

The working principles of voltage sensor are a bit complicated and varied from type to type. In general, there exists a voltage divider that allows high voltage measurement. The internal resistance is set high enough to not affect the equivalent resistance of a parallel circuit.

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PM Sensor

When a fixed intensity of light beam passes through air, the more particulate matter (PM) scatters the larger proportion of the light beam away to other directions, and hence less light beam hit the photoelectric element on the other side. Photocurrent is triggered when light hit the photoelectric element, which is then converted into density of particulate matter in air by the microcontroller. The values (most commonly seen and health-related are PM2.5 and PM10) represent the diameters of particulates in terms of micrometer (µm).

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Oxygen and Carbon
Dioxide Sensor

The oxygen sensor involves electrochemical mechanism which makes use of the linearity between an output voltage against concentration of oxygen. Carbon dioxide, on the other hand, is measured by similar method as PM sensor but this time Infrared is adapted instead and you know - carbon dioxide is a greenhouse gas perfectly absorb Infrared radiation.

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Temperature and
Light Sensor

These sensors work in above-mentioned principles. The electrical output across a thermoresistor is used to determine temperature. The light sensor relies on the famous photoelectric effect from Albert Einstein where photocurrent is generated across photocell upon receiving light. The photocurrent is then converted into corresponding light intensity.

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UV and Soil pH Sensor

Similar to light sensor, UV sensor consists of a photocell that generates photocurrent upon a specific range of Ultraviolet radiation. Soil pH sensor contains anode and cathode that utilizes the very defining nature of pH - concentration of Hydrogen atoms. The higher conductivity, so as current, infers higher concentration of Hydrogen atoms (more acidic, lower pH).

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Accelerometer

The design of modern digital accelerometer is electronically a bit complicated yet physically simple. Instead of a metal ball, the accelerometer contains structure known as "polysilicon springs" in 3 axes that deform upon inertial movement and give different capacitance. Our team decided to develop an external accelerometer even though we easily have one in mobile devices - to allow more vigourous testing without risking your valuable smartphones!

Address

The Hong Kong Polytechnic University
Hung Hom, Kowloon
Hong Kong

Contact

albert.choy@polyu.edu.hk 
Dr. Albert S. H. Choy
Teaching Fellow

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