Digital thermometer or thermostat projects have been around for many years. This project, in order to be appealing in such explored subject, incorporates a number of interesting features, never put together in one single circuit and, some of them, only available on professional equipment. The first characteristic that is worth noting is that the circuit, from now on called Meter, also measures relative humidity. As temperature and relative humidity Measurements are taken, the Meter keeps record of observed maximum and minimum levels. Each reading is also compared to user set maximum and minimum limits which, if exceeded, will trigger outputs that may be used to drive external circuits. Temperature measurements are made in either Celsius or Fahrenheit degrees. A digital clock keeps track of time, day, weekday, month and year which is an important information when the Meter is collecting and storing measurements in its microcontroller EEPROM.

The temperature and humidity meter entire setup is configured and developed using Microchip 18F 4525 controller with assembly programming firmware support.  This project is having multiple Menu configuration setup with Respect to S1,S2,S3 switches, along with that Analog signal configuration and low battery detection  and update temperature relative humidity  stored in inbuilt EEPROM of PIC18F4525 controller and we can record time intravel between minimum and maximum  measurement of temperature and humidity. Visual Basic is front end tool is used for user friendly configuration to set maximum and minimum temperature and relative humidity and it’s having more user friendly selected option like temperature measurements are made in either Celsius or Fahrenheit degrees, program memory read configuration  and meter configuration.

The Entire setup is design with appropriate schematic, visual basic frontend and various hardware selections to design this meter.
 

Update July 18, 2013

Added MCU source code. This was written in mikroElektronica BASIC (pbas). The archive also contains the code in assembler and the HEX file.