mobileVision - Portable low-cost retinal imaging device


University: William Marsh Rice University
Team Members:  Richard Latimer, Adam Samaniego, Kevin Beale, George Chen and Minhee Park

Advisors: Gary Woods, Ashutosh Sabharwal, and Ashok Veeraraghavan

TI Parts Used:

  • MSP430F5437IPN
  • OPA567AIRHGT
  • REG1117FA-5.0KTTT
  • TL2575-33IKTTR

Project Description

A mobileVision of Rice University invented a device that allows untrained individuals to take snapshots of a retina outside of a clinical environment for remote diagnosis. The smartphone-based screening device allows people in undeveloped countries to be diagnosed for vision problems and such ocular diseases as glaucoma and diabetic retinopathy. Ophthalmologists can then view the images and diagnose patients from afar. Our aim is to engineer a two-part vision screening system capable of performing basic optometric measurements and capturing wide-field retinal images. By using a modular optical front-end and leveraging the computational power of a smartphone, this device will be extensible, portable, and cost-effective.

According to the World Health Organization, 285 million people worldwide are visually impaired, the overwhelming majority of which reside in developing countries. Half of these cases are due to uncorrected refractive error, which could be corrected if proper optometric equipment were available. The other half are the result of ocular pathologies such as glaucoma and diabetic retinopathy, which could be diagnosed and monitored if a means of proper retinal imaging was available. Current eye diagnostic systems are expensive, immobile, and require a trained technician for operation. Because of this, proper ocular healthcare is reserved almost exclusively for developed countries. MobileVision aims to defy this paradigm by creating a novel system for ocular health diagnostics.

The team won $10,000 first place award in Texas Instruments' fifth annual Analog Design Contest. 

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Features
  • Winner of Texas Instruments 2012 Analog Design Competition and many other awards Check out the full article
  • MSP430F5437IPN (16BIT MCU 256K FLASH 80-LQFP) We needed a microprocessor to control a number of board peripherals and enable communication with a smartphone.  We chose this particular microprocessor for its ease of use when coupled with the MSP430-ware driver library and because of the following features:
  • Hardware timers provided PWM control signals for output N-Channel MOSFETS (to enable the high current PWM outputs for power LED's) with minimal software over-head.
  • Native I2C support provided I2C control stream to output DAC (to generate rail-to-rail DC output voltage for electronically adjustable lens) with minimal software overhead.
  • Native UART support allowed easy connection with bluetooth serial emulator (to establish communication with smartphone) with minimal software overhead.
  • Sizable memory space enabled maintenance of a board-wide nite-state machine so that any smartphone running the mobileVision app could poll the board for its current state and adjust/verify any of the board's outputs. 
  • Small size (80-pin LQFP) kept board size (and weight) to a minimum, increasing portability.
  • OPA567AIRHGT (OPAMP GP R-R 1.2MHZ 12VQFN) Our 0-3.3V DAC needed to be level shifted to 0-5V, and needed the ability to supply 400mA of current at 5V. We chose this particular operational amplier because of the following features: 
  • High current (2A), rail-to-rail output enabled adjustable 0-5V DC board output (to control electronically adjustable lens).  
  • High quality board heatsinking through thermal pad enabled operation without bulky o-board heatsink, saving weight and making the board more physically durable.  
  • Adjustable current limit enabled worry-free operation of the electronically adjustable lens (which can be damaged if driven with over 400mA of current).   Thermal ag/shutdown enabled worry-free operation even when driving high currents.  
  • Small size (12-pin QFN) kept board size (and weight) to a minimum, increasing portability.
  • REG1117FA-5.0KTTT (LDO REG 5.0V 1A D2PAK-3) Our board needed a 5V low noise supply to power an electronically adjustable lens (rated for 400mA) and some optional LED's. We chose this one in particular because it could power the lens and also because of the following features: 
  • Internal current limit allowed PWM driving of high current LED (rated for 1A, 3.3V)without need for external high power current limiting resistor, reducing board complexity, cost and size (Note: we did not need to have the lens powered when driving this particular LED).   Thermal overload protection enabled worry free operation even when supplying high currents to the rest of the board and peripherals.   Large SMT heatsinking tab allowed entire 5V power plane to be used as an elective heatsink (as opposed to a bulky o-board heatsink), saving weight and making the board more physically durable.
  • TL2575-33IKTTR (BUCK REG 3.3V 1A D2PAK-5) Lastly, we needed a 3.3V supply to power a number of logic IC's on our board. We chose a switching regulator because of their power efficiency during operation, and because we did not need a pristine 3.3V supply. We designed our board thinking we might want to power some number of LED's using this 3.3V supply, so we sought a supply which could provide 1A.  In retrospect, it would have made more sense to use a switching 3.3V supply rated for a fraction of this current rating, and left the high current 5V regulator supply power to the various LED's. This would have drastically reduced board size and weight because of the large inductor required by this 1A switching supply.  In any event, we chose this particular Buck regulator because of the following features:
  • High eciency (88% typical) gave our board lower power consumption, and generated less waste heat, which helps make our system more ready for eld deployment.   
  • Thermal shutdown and current limiting enabled worry free operation in the harshest of conditions.   
  • Large SMT heatsinking tab allowed entire GND plane to be used as an effective heatsink (as opposed to a bulky o-board heatsink), saving weight and making the board more physically durable.

Resources

User's Guide

Project Report to come...

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