Electronic Design

EiED Online>> Disposable Solutions With Low-Cost MCUs

Portable glucose testing systems started out as a science fair project, and you probably know how much I support science fairs. Our fair in Mercer County just finished up in March. That was just one reason why I was excited to hear about Home Diagnostics’ Sidekick (see Fig. 1)
.

The Sidekick, a disposable glucose testing system priced at under $35, is based on Texas Instrument’s MSP430 microcontroller (see Fig. 2)
. The MSP430’s ability to handle analog data and drive an LCD made it an ideal choice for Sidekick. Its low cost and low power consumption made it practical to build as a disposable product. The only other chip in the system is a custom ASIC (see Fig. 3)
that helps with the sensor data conversion.

Going disposable is not just for convenience. Conventional glucose testing systems require repeated calibration. With the Sidekick, calibration is done at the factory. It would still have to be calibrated if you could get another set of strips but instead you toss the unit once you have used up the strips provided. The whole system fits in the cap.

Testing consists of popping the cap to remove a strip, plugging in the strip, and getting a drop of blood on the strip. The meter does the rest with a test result displayed on the LCD.

To find out more about the Sidekick I spoke with Gary Neel, director of engineering for Home Diagnostics Inc. Here’s what he had to say:

Wong: Who came up with the idea of a disposable glucose testing system?
Neel: I came up with the idea of a disposable glucose testing while thinking about concepts for integrated test systems. All integrated systems on the market were too large, complex, and costly. My first thoughts were how to make a testing product that was small, convenient, simple and affordable. The idea to attach a meter to the cap of a test strip vial came to me one morning after our company Christmas party. The R&D group called the meter project CAP because it fit on the cap and looked like a baseball cap. The acronym CAP spawned a new catch phrase to describe this type of product as a "Convenient All-in-one Product." The formal marketing name chosen for this product is SideKick.

Wong: How does the SideKick work?
Neel: The SideKick uses a biosensor to convert glucose in blood to current. The current is then measured by a custom "BG system on chip" ASIC designed by HDI & Texas Instruments. The current is then mapped to a standardized glucose reference method to produce a calibrated result. In order to match the test strip specific characteristics with the meter, a code is assigned during manufacturing that conveys the test strip lot calibration information to the meter. This eliminates the need for the user to code the meter…and any possible coding errors.

Wong: What is the accuracy of the SideKick?
Neel: The accuracy of SideKick is equivalent to non-disposable full-featured monitors.

Wong: How does the SideKick compare with other glucose testing systems?
Neel: The SideKick is the smallest glucose monitor on the market. It provides quick test results (5 seconds), uses a low blood volume (1ul), stores results in memory, and requires no coding steps.

Wong: What is the basic architecture of the SideKick? (processor, sensors, etc.)
Neel: The SideKick employs a custom ASIC with a MSP430 microcontroller, RAM & flash Memory, LCD controller, and biosensor test media interface components (multi-input channel Sigma Delta A/D, D/A, temperature sensor).

Wong: Are there any special technologies employed by the SideKick?
Neel: Special technology was required in several areas to meet the system goals. We needed low power electronics to use a small battery, high accuracy, low noise analog performance for the test media interface, and a very high level of integration to meet size requirements.

Wong: Why did you choose the MSP430?
Neel: The MPS 430 Microcontroller family is designed for use in high-integration applications that require very low power. Texas Instruments had the skill to integrate high quality analog and digital circuits on one substrate to achieve the desired performance and integration at a low cost.

Wong: What development tools did you employ?
Neel: We used Texas Instrument’s low-cost development tools ($99) for initial feasibility code development, and later designed a custom HDI application development board. The IAR Systems C complier/assembler/linker/debugger was used to develop the firmware application.

Wong: What programming language is the application written in?
Neel: Application was written in C language.

Wong: How large is the application?
Neel: The application was under 16 Kbytes.

Wong: Was an operating system required, and, if so, what is it?
Neel: No operating system was required.

Wong: What type of self-test hardware and software is employed in the SideKick?
Neel: There are several self-tests employed to check the analog calibration, memory integrity, and battery level.

Wong: Did the design of the test strip affect the design of the hardware and software?
Neel: We used an existing test strip design for this project to reduce time to market.

Wong: What challenges did you encounter in designing SideKick?
Neel: \[One of\] the major challenges we faced was packaging all the meter components in a small enough space to fit on top of the test strip vial. The high performance custom chip also had to work on the first spin to meet our aggressive product timeline.

Wong: How did you come up with the number of test strips that would be included in the package?
Neel: The number of test strips (50) was picked to give the customer the best value. We wanted this product to be the most affordable choice for diabetic testing. HDI’s company goal is to provide quality diabetes test products at an affordable price.

Wong: How did you test the SideKick?
Neel: SideKick electronics are tested while in pc-board panel form using custom designed, high volume/precision manufacturing test fixtures. This reduces the labor cost of calibration and functional test time to a minimum.

Wong: What went right with the SideKick project?
Neel: Working with the Texas Instrument MSP 430 group was the best experience for making such a complex ASIC. They had all of the technology components \[we needed\] to meet our project challenges. They also had an aura of great confidence in their engineering ability and management skill to execute the overall process from idea to production chips. This confidence was validated when the chips were delivered ahead of schedule and worked. This never typically happens without a second or third chip spin to get production quality chips. Texas Instruments provided a high level of technical management to support this project (Thanks goes to Juan Alvarez and Herb Gingold).

Wong: What things would you have liked to have done differently given 20/20 hindsight? Neel: This was a project everyone was very excited about from the very beginning. Everyone who saw the concept said, "wow!" Response to meet the project challenges from the HDI project team, supporting outside project teams at Texas Instruments, and CSP Technologies was excellent.

Wong: How is the SideKick doing in the market?
Neel: The SideKick is doing very well in the market, and continues to fill the need as the smallest, most "Convenient All-in-one Product," and affordable choice for diabetes testing.

And now for a few of the product details:

Regulatory Approvals:


Approving Body: FDA
Identification Number: K051147
Date of Issuance: July 12, 2005

Dimensions and Weight:
2.59- by 1.65-in (widest point)
1.28 oz.

Suggested Retail Price:
$34.99

Related Links
Home Diagnostics
www.hdidiabetes.com

Texas Instruments
www.ti.com

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