THE SENSORS & THEIR INNER WORKING
The sensors units are modular and use off-the-shelf sensors and microprocessor components to create a low cost and durable package that can be set up at any location using either Wifi or GSM connectivity.
THE SCIENCE AND HARDWARE
SDS011
Particulate matter Sensor
This sensor is used to measure PM10 and PM2.5 particles for concentration ranges between 0-999µg/m3. It uses laser scattering principle to get particles concentration between 0.3 to 10ug in the air. Air gets in through the pitot inlet, then it passes through the detection area before being ejected from the sensors through the built fan. Laser scattering can be induced when particles go through the detection area. The scattered light is transformed into electrical signals and these signals will be amplified and processed. The number and diameter of particles can be obtained by analysis because the signal waveform has certain relations with the particle diameter. It has a response time of 10 seconds with a change of scene, making data collection near real time.
DHT22
Temperature and Relative Humidity Sensor
The sensor is used to measure temperature and the humidity. It uses a capacitive humidity sensor and a thermostat to measure the surrounding air, and spits out a digital signal on the data pin.
NODE MCU
Microcontroller
The NodeMCU is an open source software and hardware development environment. This is the mini computer that reads data from and controls the sensors. Unlike other microcontrollers, it has a wifi module onboard making communication of IoT projects a breeze. With 4mb of RAM, it rates higher than other boards in its class.
GSM SIM800L
Communication
The SIM800L is a low-cost cell-phone module. It supports quad-band GSM/GPRS network and is available for GPRS and SMS message data remote transmission. The board features compact size and low current consumption. With power saving technique, the current consumption is as low as 1mA mode.
PMS5003
Particulate matter Sensor
This sensor is used to measure PM1, PM10 and PM2.5 particles. It uses laser scattering principle to get particle concentration from 0.3 µg in the air, i.e by scattering using a laser to radiate suspending particles in the air, then collect scattering light in a certain degree, and finally obtain the curve of scattering light change with time. In the end, equivalent particle diameter and the number of particles with different diameter per unit volume can be calculated by microprocessor based on MIE theory.
GSMSIM800H
Communication
The SIM800H connects to any global GSM network, using 2G SIMs. It can be used to send and receive SMS messages, make and receive voice calls, send and receive GPRS data and has an AT command interface. This module has an onboard LIPO charging circuitry that enables you to charge it via USB on the go.
SIGFOX
Communication
Sigfox is a low power wide area network, ( LPWAN), whose current standards support upto 140 uplink messages, each of which can carry a payload of 12 octets and at a rate of upto of 100 bits per second. The technology uses a radio-based network.
Outdoor AQ Monitor Model 3 (GSM + Solar
Air Quality Monitor
This outdoor air quality monitor is the first to use our custom enclosure design. The monitor/kit is specially designed to work in locations where there is either no (or only intermittent) electricity, Wi-Fi, and/or Sigfox coverage. Deployment, maintenance and monitoring is made easy due to the independent nature of the kit. The kit houses a NodeMCU, a custom PCB, PMS5003 particulate matter sensor, temperature & humidity DHT22 sensor, power bank and 1200mAH LiPo battery for the GSM module. This monitor offers good resistance from degradation due to environmental factors such as UV radiation and rain. The kit is the base design concept for future iterations of the outdoor air quality monitor.
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