Soil Testing Data Logger Mid-Semester Presentation October 7, 2010

Team Members Cody Griffin Op Amp Circuitry PCB Design Hardware Testing Normal Mode Design Electrical Engineering Daniel Herrington Software Design Lead VDIP Communication Software Testing Website Design Electrical Engineering Ashley Stockbridge RTCC Software Design Test Mode Design Normal Mode Design Software Testing Electrical Engineering Matt Weissinger PCB Design Op Amp Circuitry Hardware Testing Component Research Electrical Engineering

Outline Background Problem Solution System Overview Constraints – Technical – Practical Trade Offs Timeline Progress

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 Soil Potential Input Circuit StorageMicrocontroller Power Supply Temperature Input

System Overview Temperature Input Soil Input (±600mV) Summer Circuit Pic24 μC USB Storage VDIP Power Supply 1.25 V Reference

Constraints Technical Constraints Practical Constraints

Technical Constraints ConstraintDescription InputsThe 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 Input Range The device must be able to measure temperatures that range from -10°C to 85°C. Data StorageThe device must store soil redox potential and temperature data on a removable USB storage device. Sample RateThe device must store sample data every 20 minutes.

Practical Constraints TypeConstraintDescription ManufacturabilitySizeThe size of the circuit board must be no larger than 3.1” x 3.9”. EnvironmentalOperating ConditionsThe device must be able to operate in extreme weather conditions.

Manufacturability No larger than 3.1” x 3.9” Easily accessible for routine maintenance Organized for easy assembly

Environmental Cleveland, MS

Design Issues High Impedance Soil Probes Possible Negative Input Voltages Accuracy Constraint

High Impedance Soil Probes

Soil Input Circuitry

Voltage Shifting Op Amps Low Power Supply Low OffsetRail To Rail Output Quad Op Amp IC Component Chosen LT1496 OP290

Voltage Regulators Lower PriceAppropriate Temperature Range High AccuracyComponent Chosen LM385 LT1634

Microprocessors Required I/O Quantity Battery Powered Lower Power Consumption Higher Performance Component Chosen PIC24F PIC24H

Timeline AugustSeptemberOctoberNovember Research Hardware Design Software Design Prototype Testing Final Product

Progress Hardware Design – 100% Complete – High Impedance Voltage Follower Circuit – Complete – High Accuracy Voltage Summer Circuit – Complete Software Design – 40% Complete – RTCC – Complete – Test Menu – Complete – VDIP1 Communications – 90% Complete – Normal Operation Mode – 10% Complete

Hardware Design

Hardware Testing 1.469

Software Design

References 1. PIC24F/H 2. Weather Chart 3. Other Data Sheets

Questions?