Measuring temperature and humidity is pretty easy task when proper sensor is used. Embedded-lab suggests building simple meter that uses DHT11 sensor attached to PIC16F688 microcontroller. Values are displayed on four large 7 segment LED displays. LEDs are driven using MAX7219.
There is also a LDR resistor attached which measures ambient light that is read by microcontroller internal ADC. Value is used to adjust brightness of display LEDs. Meter is capable to display temperature values in Fahrenheit and Celsius depending how RC3 microcontroller pin is pulled (low or high). Relative humidity is displayed in percents. Software keeps switching between temperature and humidity constantly.