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Transcript
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 • • • • • 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?