Download Biologically Inspired Sensor: Expansion of the Automatic Gain

Biologically Inspired Sensor:
Expansion of the Automatic Gain
Control Circuitry
A Wyoming EPSCoR Undergraduate Research Presentation
By Jennifer Beman
Dr. Steve Barrett
College of Engineering and Applied Science
Electrical and Computer Engineering Department
Overview
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Introduction
Background
Description of Research
Procedure
Future Work
Introduction
• The fly eye inspired sensor
– Fast extraction of image features with low computational
load
– Characterized in laboratory settings
– Automatic Gain Control Circuitry (AGC)
• Further Development of the AGC
– To be applicable in real world situations
• Automatic calibration
• Adjust to ambient lighting conditions
Background
• Seven lenses
– Each lens has seven photodiodes
– Gaussian surfaces from each photodiode
– Transimpedence amplification
Background
• 49 mechanical potentiometers
– Gaussian surfaces with varying height and voltage
– Calibration by hand is required
Potentiometer
Description of Research
• Design a microcontroller based system for
characterization of the sensor
– Eliminate the need for hands-on characterization
– Digital potentiometers in place of mechanical
– Redesign transimpedence amplifier
• Impedances available are much smaller
– Single cartridge design
• PC Board design
Structure of System
• Initial Design for microcontroller based system
Transimpedance
Amp
Transimpedance
Amp
Structure Diagram
Microcontroller Flow Chart
Potentiometer
Adjustment
Input calibration
voltage
Read in voltage
through ATD
7 conversions,
one on each
channel
no
Calculate actual
voltages
For each channel
Calibrations
successful?
yes
Calibrated to
input voltage?
Calculate
necessary
impedence
Set pot position
through PORT
Calibration Flow Chart
System Considerations
• Three possibilities examined
– No memory
• Recalibration required every power down
– Memory on microcontroller
• Can reset potentiometers to their last position
– Memory onboard potentiometers
• Potentiometers can reset themselves to their last
position
Problem Encountered
• Transimpedance Amplifier
– Constraints
• Currently using 2 MegΩ potentiometers
• Digital potentiometers up to 100 kΩ
• Dig pots with onboard memory up to 10 kΩ
– Gain of current design
• Gain V0  I sc  RL  (1  RF )
R
• Ranges from 4 to 8 Meg
• Need 20 100 kΩ potentiometers with current design
Redesigning
• Desire similar range in gain
– Simple I-V converter
– Gain: V0  1 
R2 R2

R1 R3
– Gives range of 2 to 12 Meg
• Step size in gain about 100k which is too large
4.8
– Adjust to get desired step size and gain
– Continue to develop the amplifier
4.6
4.4
4.2
X: 465
Y: 3.968
4
3.8
3.6
3.4
0
100
200
300
400
500
600
700
800
900
1000
Technology
• Microprocessor
– Atmel
• Ports needed:
– ATD PORT
– SPI system
• Potentiometers
– MCP41010-I/P IC
• 10k ohm, 256 steps, SPI
– MCP42010-I/P IC
• 2ch, 10k ohm, 256 Steps, SPI
Future Work
• Complete design of new transimpedance amplifier
• Build single lens calibration system
• Test single lens system extensively
• Expand successful system to 7 lens design
Questions?