Real-time Wireless Temperature and Humidity Monitoring Systems

The monitoring of environmental variables such as temperature, pressure and humidity has a long history of development and the variables have shown significant impact in the productivity of plant growth, the quality of food industry and the efficiency of many temperature and humidity-sensitive equipment.

The monitoring of temperature and humidity of restaurants, greenhouses, lab facilities, grocery stores and server rooms is important with respect to productivity. The reliable measurement and monitoring is crucial in this competitive era of technology.

Monitoring Setup

The temperature and humidity data is sensed using the humidity and temperature sensors and then the sensed data is transferred to the monitoring stations. The sensors are controlled through microcontrollers and data transmission process can be done simply and effectively using cloud-based databases. For data monitoring, Graphical User Interfaces are developed in a way that the client needs are fulfilled.

Temperature and Humidity sensors

A sensor is an electronic device that converts a change in physical phenomenon into an electrical signal. It can send the information to computers or other electronic devices. Therefore, it is a part of the interface between the environment or physical world and the electronics.

The function of a sensor is to respond to an input physical signal and to convert it into an electrical signal (voltage). It is a semiconductor device that is designed to respond to change in their resistive or capacitive property depending upon the type of sensor.

The performance of a sensor is characterized by:

  • Transfer function,
  • Sensitivity, Range,
  • Accuracy/Uncertainty,
  • Hysteresis,
  • Linearity,
  • Noise,
  • Resolution and
  • Bandwidth.

The DHT11 Sensor

The sensors used in this work is temperature and humidity sensor-DHT11. The sensorDHT11 is an Analog sensor designed to sense the physical change in heat and moisture when exposed in air with suitable wiring and programming.

Its small size, cheap price, low power consumption, quick responses are the characteristics for being one of the best choices for many users. The sensor DHT11 is applicable in HVAC (heating, ventilation and air conditioning), it can be used in testing and inspecting equipment and consumer goods. It is also applicable to use in building a weather station or a humidity regulator.

The use of DHT11 sensor has shown its usefulness measuring and controlling temperature and humidity in home appliances, medical and many other sectors. DHT11 has following performance range and accuracy:

  • Temperature: 0 to 50°C
  • Humidity: 20 to 90 % RH
  • Accuracy: Temperature: ±2 % Humidity: ±5 % Where the operating Voltage remains between 3V to 5.5V 

Humidity Monitoring

Humidity is defined as the amount of water vapour contained in air. Usually, it is expressed as absolute humidity, dew point and relative humidity. The sensor used in this thesis project, DHT1, is designed to measure humidity in terms of relative humidity (RH).

Relative humidity (RH) is the ratio of the amount of water vapour content of the air to the saturated moisture level at the same pressure or temperature: 𝑅𝐻 = 𝜌𝑤/𝜌𝑠 × 100 %, where 𝑅𝐻 is relative humidity, 𝜌𝑤 is the density of water vapour, and 𝜌𝑠 is the density of water vapour at saturation.

The sensor DHT11 detects moisture in the air by measuring the electrical resistance between electrodes. It is fabricated with a moisture holding substrate. When substrate absorbs moisture, ionization takes place and results in the increase in conductivity between the electrodes. The relative humidity is proportional to the change in resistance between electrodes due to moisture absorbed.

Data Transmission

Data transmission can be done through an IoT based cloud. The method is very simple and effective. Internet of Things (IoT) describes an emerging trend where a large number of embedded devices (things) are connected through the Internet.

These connected devices communicate with people and other things and often provide sensor data to cloud storage and cloud computing resources where the data is processed and analyzed to gain important insights. Cheap cloud computing power and increased device connectivity is enabling this trend.

Monitoring system

In this context, a monitoring system generally refers to an automated system that simultaneously and continuously records and visualize temperature and humidity parameters at one or more predefined points. A monitoring system is used to record and document the conditions in various storage areas whilst minimizing the need for manual measuring and recording. Such a monitoring system is increasingly required in facilities storing TTSPPs.


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