Transcript Remote Finder - University of Iowa

TEMPERATURE AND HUMIDITY SENSOR
Designed by:
John Haines
Kevin Zavodny
WHAT DOES IT DO?
•
Grabs Temperature and Humidity measurements every 4 seconds.
•
Displays the current Temperature in degrees Celsius and humidity in percent RH
•
Downloads the raw data to an external EEPROM Chip
•
Allows the user to read data from EEPROM via RS232 and then plot in Excel
SHT15 TEMPERATURE & HUMIDITY SENSOR
•
Has a unique capacitive sensor element used for measuring relative humidity
•
Temperature is measured by a band-gap sensor
•
Temperature conversion equation ( reading*.01) – 40 = Temp in Celsius
•
Humidity conversion equation ((-2.8*10^-6)*(reading^2) + reading*.0405) – 4 = RH
•
Before each command is sent a start sequence is required
•
Initially had issues because it was only partially I2C and we found we had to use different ports
other then the SCL and SDA lines. However we were able to solve this problem
OSCILLOSCOPE SCREENSHOT
OF SHT15 DATA OUTPUT
EXTERNAL EEPROM
•
Start sequence is initiated by pulling the SDA line low
•
Next the control byte is sent via I2C to select the proper chip
• 1010 already given
• Next 3 are chosen by either grounding or connecting to Vcc
• Last bit is the Read/Write bit (0 for write, 1 for read)
•
Next the data to be saved is sent over followed by the Stop Sequence
•
The stop sequence is a low to high transition of the Data line
•
Reading from the Chip is essentially the same process except that the Read/Write bit is
set to 1 and the data is then output through the usart to our pc for data plotting
EXCEL PLOTS FROM DATA LOGGED
100
90
80
70
60
50
Temperature
Humidity
40
30
20
10
0
1
2
3
4
5
6
7
8
9
10
11
12
13
DEMO
PROBLEMS AND ISSUES
•
Having a few issues reading the data from the EEPROM
•
We currently are putting the micro to sleep between measurements and having it wake up
via the Watchdog timer, but are having some difficulty getting it to sleep for the
appropriate amount of time
PRACTICAL APPLICATIONS