educ8s.tv has posted a video tutorial on building an advanced Arduino data logger that records temperature, humidity, barometric pressure, and ambient light intensity on a micro SD storage card. It uses some easily available sensors, like DHT22, BMP180, and BH1750, for sensing the surrounding environment and the DS3231 RTC module for time-stamping the measurements. The tutorial describes in steps how to setup the complete project on a breadboard. The data logger runs for about 2 weeks using simple AA batteries and the data are stored on the SD card in a .csv file for easy transport to PC for further processing.
Arduino data logger
A couple weeks ago I received some sample products from Dorji Applied Technologies, a china-based company that make varieties of RF and sensor modules. One of the products I received was their latest DSTH01 sensor module that carries Silicon Labs’ Si7005 digital relative humidity and temperature sensor on board. Things I liked about it are it is inexpensive (available on Tindie for only $6), compact, and most importantly it supports I2C host interface for communication.
DSTH01 module with Si7005 sensor onboard
Pin diagrams of DSTH01 sensor module
Your favorite plants need plenty of water to grow. If you keep forgetting to water your house plants you might be interested in this plant watering alarm device called Chirp. Chirp uses capacitive humidity sensing technique to measure the moisture level in the soil and alerts the user through short chirps when it is time to water the plant. Based on the amount of ambient light detected by the on-board light sensor, Chirp detects day and night condition. It is very considerate and remains silent during the night time. The project uses ATtiny44A and is licensed under CERN Open Hardware Licence v.1.1.
Chirp: Plant watering alarm
Measurement and control of temperature and relative humidity finds applications in numerous areas. These days devices are available which have both temperature and humidity sensors with signal conditioning, ADC, calibration and communication interface all built inside them. The use of such smart sensors greatly simplify the design and reduces the overall cost. We discussed in past about Humidity and temperature measurements with Sensirion’s SHT1x/SHT7x sensors. These sensors are capable of measuring both temperature and relative humidity and provide fully calibrated digital outputs. While SHT1x/SHT7x are very accurate sensors, they are still expensive for hobbyists use. This articles discusses the DHT11 sensor which also provides calibrated digital outputs for temperature and humidity but is relatively lot cheaper than the Sensirion sensors. The DHT11 sensor uses a proprietary 1-wire protocol which we will be exploring here and implementing with the PIC16F628A microcontroller that will receive the temperature and humidity values from the sensor and display them on a 16×2 character LCD.
Interfacing DHT11 sensor with PIC16F628A
In Part 1 of this tutorial, we discussed about Sensirion’s SHT1x and SHT7x series of humidity sensors, their interface specifications, the communication protocol used for transferring data in and out of the sensor, and the equations to convert their digital outputs to actual physical quantities. These sensors are capable of measuring temperature along with relative humidity and provide outputs in fully-calibrated digital words. We will now see how a PIC microcontroller can be programmed to communicate with these sensors, read the temperature and relative humidity data, and display the information on a character LCD.
Circuit setup on breadboard