I have published details of a Temperature and Humidity display and logger before. It was based around a 2x16 or a 4x20 LCD display using a SD card to log the values.
I wanted to create something that looked better and could be put on display in a case or panel. Also I wanted it to be more flexible in what it can be used for.
It displays the temperature and humidity of two DHT sensors along with the time and date. It logs the values on an EEPROM and plots graphs.
I used a 2.8" shield from ITEAD Studio http://imall.iteadstudio.com/development-platform/arduino/shields/im120417020.html
. This minimises the amount of wiring and makes it easier to build. The real time clock (RTC) and the EEPROM are both on a I2C bus. All the address pins on the EEPROM are tied low.
There is a SD card slot on the display shield, but using it on the Mega requires some extra wiring to make it work. I used pin extensions for the shield, to avoid it touching the USB socket on the Arduino. If you want to use the SD card, it is just a matter of not using the section for the pins starting at pin 8 and the using wires with female connectors on the pins hanging in mid air. The RTC and EEPROM are small enough to fit between the Mega and the display.
The shield works well with the code form Henning Karlsen http://www.henningkarlsen.com/electronics/
. He has done some good work on TFT displays.
I'm still working on improvements, but here is the code of what I have done so far.
Picture and code are attached. The code is too large to include here.
Let me know what you think. Suggestions are welcome.