Soil Testing Data LoggerMid-Semester Presentation

October 7, 2010

Team Members

Cody Griffin

Op Amp CircuitryPCB DesignHardware TestingNormal Mode Design

Electrical Engineering

Daniel Herrington

Software Design LeadVDIP CommunicationSoftware TestingWebsite Design

Electrical Engineering

Ashley Stockbridge

RTCC Software DesignTest Mode DesignNormal Mode DesignSoftware Testing

Electrical Engineering

Matt Weissinger

PCB DesignOp Amp CircuitryHardware TestingComponent 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

TemperatureInput

SoilInput

(±600mV)

SummerCircuit Pic24 μC USB

StorageVDIP

Power Supply1.25 VReference

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 Input Range

The device must be able to measure temperatures that range from -10°C to 85°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 Operating Conditions The 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

Soil Input Circuitry

Soil Input Circuitry

Voltage Shifting Op Amps

Low Power Supply

Low Offset Rail To Rail Output

Quad Op Amp IC

Component Chosen

LT1496

OP290

Voltage Regulators

Lower Price Appropriate Temperature Range

High Accuracy Component Chosen

LM385

LT1634

Microprocessors

Required I/O Quantity

Battery Powered

Lower Power Consumption

Higher Performance

Component Chosen

PIC24F

PIC24H

Timeline

August September October November

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?