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Digital Thermostat and Data Logger

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

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Digital Thermostat and Data Logger

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  1. Digital Thermostat and Data Logger Brandon Wagner and David Southwick

  2. 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

  3. 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) • Mode • Heat • A/C User Desired Temp Current Time

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

  5. 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

  6. Analog to Digital Converter 1 1 0 0 0 0 0 0 ADC Channel Select = ADC0 VREF = Internal 1.1 V 1 1 0 1 1 1 1 0 ADC Enable Start Conversion Conversion Complete INT Flag Freq Prescaler: 50-200 kHz Choose 8MHz/128 = 125 kHz ADC INT Enable • Example: Temperature is 74.8 °F • => Sensor outputs 74.8 x 10 mV = 0.748 V Resolution = 1.1V / 1024 = 1.074 mV => ADC value of 1 = 1.074 mV • LM34 outputs 10 mv / °F Convert back to °F: 696.32 x 1.074 = 747.8  display “74.7°F”

  7. Demonstration

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