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Business card scanner relies on analog

Posted: 09 Aug 2007 ?? ?Print Version ?Bookmark and Share

Keywords:business card reader and software? voltage regulator? USB host? external E2PROM?

How many times have you returned from a business trip with two dozen new business cards!and no time to type them into your computer? The CardScan is a business card reader and software package that picks up company names and logos, contact names, addresses, phone numbers and e-mail addresses. It will transfer the information into PC contact managers like Act! or Microsoft Outlook, or into PDAs attached to your computer. Even accounting for time spent double-checking the information!making sure the optical character recognition (OCR) hasn't noted, say, a capital "B" where it should have seen the number "3"!this device will save you a lot of time entering contact information into your databases.

Faster, more accurate
The latest version of the CardScan OCR scanner and software!Version 8!is faster and more accurate than previous iterations. The software does a remarkably good job of not only spelling names correctly, but also distinguishing personal names from company names, cellphone numbers from fax machines, e-mail addresses from Website URLs. On Texas Instruments business cards, for example, where two addresses are given (one for visitors, another for snail mail), the software effortlessly tells them apart. Dozens of cards can be scanned rapidly, with barely a need for touch-up.

OCR is effectively a visual pattern recognition, in which a scanned pattern is compared with a library of patterns and identified with a "best fit" algorithm. Speed and accuracy depend on analog components with high resolution and speed, as well as a fast lookup. In the architecture of the CardScan system, the analog ICs are packed along with the scanning mechanism in a 6.5 x 3.5 x 3-inch box. The pattern recognition is performed on the host.

The key component in the system is a high-speed ADC, TI's TLC5510A. This is an 8bit device with a 20MSPS conversion rate. The device, intended for video digitizing in DTV, medical imaging and videoconferencing applications, is interchangeable with Sony's CXD1175.

The converter is fabricated in CMOS, using a two-stage-pipeline architecture. Unlike the flash conversion architecture, which uses 256 parallel comparators in parallel, the semiflash architecture saves silicon real estate and power consumption. TLC5510A comes in a 24-pin plastic package and consumes 130mW typical from a 5V supply. The device includes a sample-and-hold circuit and tristate parallel outputs. That is, the outputs can be high, low or disconnected with a high-impedance mode.

Belkin's USB Hub and dongle

The latest version of the CardScan OCR scanner and software is faster and more accurate than previous iterations.
(View CardScan's OCR scanner teardown.)

The scanning mechanism is controlled by an Allegro Microsystems stepper motor driver IC, the A3966SLB. Equipped with two H-bridges, A3966 is designed to drive both windings of a two-phase bipolar stepper motor. An active-low enable input turns on the output drivers.

The CardScan's stepper motor, despite its small size, can draw a great deal of current!up to 650mA at operating voltages to 30V. Motor-winding current is controlled by a fixed-frequency pulse-width modulator. The load current limit is user selected. A copper heat sink tab at the bottom of the 16-lead plastic SOIC package dissipates heat for the A3966SLB.

A major difference between Version 8 and earlier models of the CardScan system is that the outboard power supply has been eliminated. On Version 8, power comes in through the USB interface, controlled by the TUSB6250PFC from TI.

The USB port provides a 5V line for its peripherals, though it was not originally designed for power transfer. Up to 100mA is available on the USB port for a single peripheral and up to 500mA for a five-port hub. New-generation USB switches allow up to 500mA to be transferred through USB ports and support battery-charging applications. The design trick requires additional voltage regulators and capacitor reservoirs on the peripheral side of the interface.

Suspend and resume
TI's TUSB6250PFC uses two voltages: 3.3V for its I/Os and 1.8V for its core, the latter delivered by an on-chip voltage regulator. The high-speed mode on the USB port allows 480Mbps data transfer rates. There is also a suspend/resume and remote wake-up operation built into the USB 2.0 specification (as well a device-unique serial number).

In TI's implementation, a 60MHz 8051 MCU is built into the USB interface controller. Application code is loadable from either the USB host or an external E2PROM, via the I?C interface. Some 8Kbytes of on-chip ROM serve as the boot loader, along with roughly 64Kbytes of RAM. There are 13 GPIOs and three open-drain (high-current) outputs. The TUSB6250PFC's ATA/Atapi interface controller allows the USB port to resemble a mass-storage device to the host computer.

On-board logic, which provides path steering for the scanner, includes two Fairchild MM74HCT quad two-input OR gates and a 24LC256 1 E2PROM from (we believe) STMicroelectronics. Though fabricated in CMOS, the MM74HCT devices are TTL compatible, which means they can accommodate 5V logic swings. The output swings of the TI USB controller will be 3.3V.

- Stephan Ohr
Research Director, Analog and Power Semiconductors, Gartner Dataquest

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