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


User selectable threshold temperature


Fahrenheit and Celsius
0.1° F precision via RPG rotation
H – Heating mode


Green LED active
when temp above threshold
Temperature data logger with time stamp


Red LED active
when temp below threshold
A – A/C mode


Actual Temp (C)
Heating mode or A/C mode


Actual Temp (F)
Stores temperature in EEPROM on a user selected interval
Mode
- Heat
- A/C
Serial interface to computer terminal
Commands:




“T” – Time change request
“D” – Date change request
“H” – Temperature history request
“C” – Change storage interval
User Desired Temp
Current Time
11:49
11:53
11:56
11:59
12:03
12:06
12:09
12:13
12:16
12:19
12:23
12:26
12:29
12:32
12:36
12:39
12:42
12:46
12:49
12:53
12:56
12:59
1:03
1:06
1:09
1:13
1:16
1:19
1:23
Temperature Logging
Terminal - Enter “H”
Import data to EXCEL
Temperature Vs. Time
79
78.5
78
77.5
77
76.5
Temp
Use EXCEL to plot Temp vs Time
Software


Initialize/Configure USART, LCD, I2C, ADC, and Timers
Determine RPG rotation


Check pushbutton






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



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


Toggle heat or A/C mode
Update LED outputs


Increment or Decrement desired temperature setting
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
1
1
0
0
ADC Enable
1
0
Start
Conversion
VIN 1024
ADC 
VREF
LM34 outputs 10 mv / °F
1
Conversion
Complete
INT Flag
Resolution = 1.1V / 1024 = 1.074 mV
=> ADC value of 1 = 1.074 mV
0
0
0
ADC Channel Select = ADC0
VREF = Internal 1.1 V
1
0
1
1
ADC INT
Enable
1
0
Freq Prescaler: 50-200 kHz
Choose 8MHz/128 = 125 kHz
Example: Temperature is 74.8 °F
=> Sensor outputs 74.8 x 10 mV = 0.748 V
ADC 
0.748V 1024
1.1V
 696.32
Convert back to °F: 696.32 x 1.074 = 747.8  display “74.7°F”
Demonstration