Digital Thermostat and Data Logger Brandon Wagner and David Southwick

Schematic  ATmega88PA  MAX232 Level Shifter  5V to 15V  PCF8583 Real Time Clock  LM34 precision Fahrenheit Sensor  10 mv/ °F  24LC256 EEPROM  32K x 8 storage  EVE-GA1F2012B Rotary Pulse Generator  GDM1602K 2x16 LCD  2 LEDs  Pushbutton Switch I2C Serial CLK I2C Serial DATA ADC0 pin

Features  Current Time and Temperature display  Fahrenheit and Celsius  User selectable threshold temperature  0.1° F precision via RPG rotation  Heating mode or A/C mode  H – Heating mode  Red LED active when temp below threshold  A – A/C mode  Green LED active when temp above threshold  Temperature data logger with time stamp  Stores temperature in EEPROM on a user selected interval  Serial interface to computer terminal  Commands:  “T” – Time change request  “D” – Date change request  “H” – Temperature history request  “C” – Change storage interval Actual Temp (F) Actual Temp (C) User Desired Temp Current Time Mode - Heat - A/C

Temperature Logging Terminal - Enter “H” Import data to EXCEL Use EXCEL to plot Temp vs Time

Software  Initialize/Configure USART, LCD, I2C, ADC, and Timers  Determine RPG rotation  Increment or Decrement desired temperature setting  Check pushbutton  Toggle heat or A/C mode  Update LED outputs  If A/C mode: activate green LED if desired temp < actual temp  If heat mode: activate red LED if desired temp > actual temp  If (Timer0 flag set) – set every second  Read ADC register  Convert to value to Fahrenheit and Celsius  Read RTC for date and time  Update LCD with actual and desired temp, mode, and time  If (Timer1 flag set) – set every user defined number of minutes  Format temperature and time/date from RTC into a string  Write data string to EEPROM  Process any input from USART  “H” - Read data from EEPROM  “T”, “D” - Write to data to RTC

Analog to Digital Converter V REF = Internal 1.1 V ADC Channel Select = ADC0 ADC EnableStart Conversion Conversion Complete INT Flag Freq Prescaler: kHz Choose 8MHz/128 = 125 kHz Resolution = 1.1V / 1024 = mV => ADC value of 1 = mV LM34 outputs 10 mv / °F Example: Temperature is 74.8 °F => Sensor outputs 74.8 x 10 mV = V Convert back to °F: x =  display “74.7°F” ADC INT Enable

Demonstration