Download Soil Testing Data Logger

Soil Testing Data Logger
Final Presentation
November 30, 2010
Team Members
Cody Griffin
Ashley Stockbridge
Op Amp Circuitry
VDIP Communication
Hardware Testing
Normal Mode Design
RTCC Software Design
Test Mode Design
Normal Mode Design
Software Testing
Electrical Engineering
Electrical Engineering
Daniel Herrington
Matt Weissinger
Software Design Lead
VDIP Communication
Software Testing
Website Design
PCB Design
Op Amp Circuitry
Hardware Testing
Component Research
Electrical Engineering
Electrical Engineering
Outline
•
•
•
•
•
Background
Problem
Solution
System Overview
Constraints
– Technical
– Practical
• Subsystem Tests
• Complete System Tests
• Path Forward
Background – Soil Redox Potential
• Electrical property of soil that correlates to the
specific chemicals present in the ground
• Research topic of Dr. Kroger with the Forest
and Wildlife Research Center at MSU
Problem – Chemical Runoff
• Caused by fertilizers and pesticides used on
farmlands
• Can be controlled using a detailed historical
set of soil redox data
• No efficient method for collecting soil redox
measurements
Solution – Soil Testing Data Logger
• Reduces the time associated with taking soil
redox potential measurements in the field
• Periodically takes soil redox potential and
associated temperature measurements
• Stores all measurements in a removable USB
storage device
System Overview
Temperature
Input
Microcontroller
Soil Potential
Input Circuit
Power Supply
Storage
Constraints
• Technical constraints
• Practical constraints
Technical Constraints
Constraint
Description
Inputs
The device must support four soil probe inputs and five
temperature inputs.
Soil Redox Potential
Input Range
The device must be able to measure potentials that range
from -600mV to +600mV with an accuracy of ±10mV.
Temperature Indicator The device must be able to measure temperatures that
Input Range
range from -40°C to 125°C with an accuracy of ±1°C.
Data Storage
The device must store soil redox potential and temperature
data on a removable USB storage device.
Sample Rate
The device must store sample data every 20 minutes.
Practical Constraints
Type
Constraint
Description
Manufacturability Size
The size of the circuit board must be no
larger than 3.1” x 3.9”.
Environmental
The device must be able to operate in
extreme weather conditions.
Operating Conditions
Manufacturability
• No larger than 3.1” x 3.9”
• Easily accessible for routine maintenance
• Organized for easy assembly
Environmental
Cleveland, MS
Subsystem Tests
• Hardware
– Soil Input Circuitry
– Microcontroller ADC
– VDIP1
• Software
– Real Time Clock Calendar
Soil Input Circuitry
1.250 V
Reference
R4
V+
V+
Soil Probe
+
R3
To
PIC
ADC
+
_
_
V-
R1
R2
Voltage Follower Op-Amp
Input Voltage (mV)
-1000.0
-800.0
-600.0
-400.0
-200.0
0.0
200.0
400.0
600.0
800.0
1000.0
Output Voltage (mV)
-1000.0
-800.0
-600.0
-400.0
-200.0
0.0
200.0
400.0
600.0
800.0
1000.0
Difference (mV)
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
Soil Input Circuitry
1.250 V
Reference
R4
V+
V+
Soil Probe
+
R3
To
PIC
ADC
+
_
_
V-
R1
R2
Voltage Summing Op-Amp
Input Voltage
(mV)
Reference
(mV)
-1000.0
-800.0
-600.0
-400.0
-200.0
0.0
200.0
400.0
600.0
800.0
1000.0
1250.0
1250.0
1250.0
1250.0
1250.0
1250.0
1250.0
1250.0
1250.0
1250.0
1250.0
Desired
Output
Output (mV) Voltage (mV)
250.0
450.0
650.0
850.0
1050.0
1250.0
1450.0
1650.0
1850.0
2050.0
2250.0
252.6
453.2
653.7
854.2
1054.8
1255.4
1455.9
1656.5
1857.1
2057.6
2258.1
Difference
(mV)
2.6
3.2
3.7
4.2
4.8
5.4
5.9
6.5
7.1
7.6
8.1
Voltage Summing Op-Amp
Output Error vs. Output Signal
9
Output Error (mV)
8
7
6
5
4
3
2
250
450
650
850 1050 1250 1450 1650 1850 2050 2250
Output Signal (mV)
• Linear error
• Easily corrected by
calibration in Excel
• Oscilloscope reading
• Noise less than ±1mV
Microcontroller ADC – Supply
• ADC reading is dependent upon supply voltage
• Supply voltage varies with batteries
• Back calculate supply voltage from reference
Supply Voltage
(V)
2.400
2.600
2.800
3.000
3.200
3.400
VREF Calculation
(V)
2.397
2.598
2.801
2.999
3.200
3.401
Error
(%)
-0.125
-0.077
0.036
-0.033
0.000
0.029
Microcontroller ADC – Inputs
ADC Input
(mV)
ADC Reading
(mV)
Error
(mV)
200
400
600
800
1000
1200
1400
1600
1800
2000
192
394
596
796
998
1200
1402
1603
1804
2006
-8
-6
-4
-4
-2
0
2
3
4
6
VDIP1 – Communication
• Synchronization
– Sending / Receiving ‘E’
• Sending commands
– Sending “Open For
Write” command
– Acknowledging
command
VDIP1 – File Creation
• Create file
• Write to file
• Close file
Real Time Clock Calendar
• Accurately
oscillates
• Time / Date
rollover
• Leap year
handling
Time and
Date
Rollover
Leap Year
Handling
Real Time Clock Calendar – Alarm
• Wakes up microcontroller
from sleep mode
• Precise time intervals
Complete System Tests
• High Frequency Mode
– Inputs Constraint
– Soil Redox Potential Constraint
– Temperature Indicator Constraint
– Data Storage Constraint
• Normal Frequency Mode
– Sample Rate Constraint
High Frequency Mode – VDIP1 Output
High Frequency Mode – Soil Inputs
High Frequency Mode – Temp Inputs
Normal Frequency Mode
Path Forward
• Implement minor corrections to PCB
• Assist Dr. Kroger with field testing
References
[1] “Season Weather Averages for Mid Delta Regional,” Weather Underground. 2010.
http://www.wunderground.com/NORMS/DisplayNORMS.asp?AirportCode=KGLH&SafeCityName=Cle
veland&StateCode=MS&Units=none&IATA=GLH
Questions?
Questions?