Temperature and Humidity Logging Over Ethernet I

Posted on Feb 6, 2014

A project on temperature/humidity logging a couple of years ago. In that project I logged the temperature and humidity readings in my basement lab over the course of a year. One issue with the approach I took back then was that the data could not be observed in real time because the logged data were written to an SD card and could only be re

Temperature and Humidity Logging Over Ethernet I
Click here to download the full size of the above Circuit.

trieved once the logging process was done. So naturally this time around I wanted to build a data logger with better capabilities. One way to obtain real time data is to stream the logged data over the Ethernet so that the data can be logged, processed and then displayed on a PC. And this is the approach I took. The Ethernet chip Arduio officially supports is WIZnet`s W5100. But it seems that Microchip`s ENC28J60 based controller boards can be had at a much lower price point and several libraries (like this one ) already exist so I decided to give that a go. The temperature/humidity sensor I used in this project is Sensirion`s SHT21. I have used it in many of my projects before and it is very easy to use with various libraries readily available. One thing to note is that the maximum Vcc for SHT21 is around 3. 3V. So if you were to use 5V on your MCU, an I2C level translator (i. e. TI`s PCA9517 ) needs to be utilized in order to avoid damage to the sensor. The ENC28J60 module I used can be obtained on eBay for less than $5. Since both the sensor and the Ethernet module operate at 3. 3V, it is much easier to power the MCU at 3. 3V as well so that we do not have to worry about voltage level translations. While ATmega328p is not rated to run at 16Mhz at 3. 3V, in normal cases this shouldn`t be an issue. Since the default Arduino fuse settings assume a 5V supply voltage, you might need to adjust the fuse settings in situations...

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