Using LEDs, LCDs and GLCDs in Microcontroller Projects

12.6 PROJECT 12.6 – Temperature and Relative Humidity Measurement

12.6.1 Project Description

This project demonstrates how the ambient temperature and relative humidity can be measured and then displayed on the GLCD.

In this project, the SHT11 relative humidity and temperature sensor chip is used. This is a tiny 8-pin chip with dimensions 4.93 × 7.47 mm and thickness 2.6 mm, manufactured by Sensirion (http://www.sensirion.com). A capacitive sensor element is used to measure the relative humidity, while the temperature is measured by a band-gap sensor. A calibrated digital output is given for ease of connection to a microcontroller. The relative humidity is measured with an accuracy of ±4.5%RH and the temperature accuracy is ±0.5°C. Operating voltage ranges from a minimum of +2.4 V to a maximum of +5.5 V.

Figure 12.34 shows a picture of the SHT11 sensor. The sensor is available as a small PCB that can be plugged into a development board (e.g. EasyPIC 7) for ease of use.

Figure 12.34 The SHT11 sensor

The pin configuration of the sensor is as follows:

Pin 1: Gnd pin.

Pin 2: The Data pin. This pin is used to transfer data in and out of the sensor. When sensing a command to the sensor, the data is valid on the rising edge of the clock input (SCK). When reading data from the sensor, data is valid 200 ns after the clock goes low and remains valid until the next clock.

Pin 3: The Clock ...