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Test your blood in a Breeze

Posted: 15 Jun 2007 ?? ?Print Version ?Bookmark and Share

Keywords:blood glucose monitors? BGMs? consumer electronics? SoC?

Personal blood glucose monitors (BGMs) have evolved to become affordable and highly portable electronic devices. The BGMs in use today are little electrochemistry labs.

The Ascensia Breeze, made by Bayer AG, is one of several major brands of BGMs. All rely on the same bASIC techniques for measurement: A small sample of blood from a skin prick is collected and supplied into a chemical reaction by way of a test strip or sample collector, which interfaces to system electronics for electrochemical analysis.

Error-free data coding
Ascensia brings a level of convenience to monitoring by the use of a disk containing the chemistry needed for measurements. The individual test strips of many other meters are replaced in the Breeze by an inserted cartridge disk system that holds 10 sample strips.

Whereas traditional meters require the user to manually enter the coding data stamped on the sample strip box to adjust for variable reactivity, with the Ascensia Breeze the coding information is built in. By eliminating the human dimension of data entry coding, the smart disk ensures that error-free calibration data is automatically known.

As with consumer electronics of all stripes, ease of use applies: To perform a test, the user simply opens the meter, inserts a 10-test disk and cycles the pull bar at the Breeze's lower end to expose a test strip. After applying the blood sample, the reading is ready to be taken.

Tiny electrochemistry lab
I didn't buy a disk, so I can't speak to the particulars inside that consumable element of the design. But the presence of a polymer-thick-film flex circuit in the Breeze suggests an electrical readout of calibration information from the disk, perhaps stored in a small, inexpensive serial memory chip or even through something as simple as a laser-trimmed resistor. The connecting flex circuitlocated on the flip door used to house the diskmakes contact by spring-loaded pin fingers. Signals are then routed to the door hinge, where a zebra strip connector routes the connections to the circuit board assembly in the enclosure portion of the Breeze's clamshell design. (Back to that point in a moment.)

A fairly complex mechanical apparatus in the main clamshell housing contains the indexing apparatus both to present a test strip from the disk and to index to new test strip sites when the test is complete. A rotating ratchet mechanism spins the disk a notch after every use by translating the reciprocating motion used to expose the strip into a rotary motion simultaneously.

Ascensia Breeze from Bayer

While traditional meters require the user to manually enter the coding data stamped on the sample strip box to adjust for variable reactivity, with the Ascensia Breeze the coding information is built in.
(View Ascensia Breeze's teardown diagram)

The Breeze's single rigid circuit board is home to three chips, all of which are powered by a single Lithium coin cell battery. Starting with the business end of the design, a custom ASIC (3600025H) is responsible for the electronics side of the electrochemistry used in the glucose monitor. Given the proprietary nature of the chip, details are sketchy; but to a first order, the part must be supporting the coulometry used as the basic glucose measurement technique.

Constant current (amperostatic) or constant voltage (potentiostatic) coulometry essentially counts the number of electrons needed to complete the reaction of the test strip chemistry and the blood sample. Glucose levels are presumed to correspond to differing coulometric readings acquired in the mostly analog ASIC, and the disk's calibration data is also connected to the chip by way of the previously mentioned flex circuit connector.

Once the ASIC has completed its electrochemical test measurement and is calibrated for coded reactive variations, the output is sent to an NEC microPD78F0338GC microcontroller. No ADC from the ASIC is obvious at the die level, so it seems plausible that signal conversion takes place in the NEC part's internal ADC, where it can be manipulated to a displayed glucose level on the Breeze's segment LCD. The LCD is driven directly by the MCU, which also handles the button input. Likewise, the NEC device is used to interface to the product's headphone-style connector, which implements a data port to allow the unit's 100-reading memory to be downloaded for analysis on a host PC. A 4KByte E2PROM from Catalyst is used to hold reading data for review or download.

Consumables are about $6 to $9 per disk. The Breeze meter likely has manufacturing costs in the $10 to $15 range-a fraction of its $70 to $80 price.

Noninvasive BGM solutions are on the drawing board, but none has reached commercial consumer cost targets with the accuracy of direct measurement. Until that is achieved, the coulometry and supporting electronics of the invasive BGM have been enhanced with automated sample processing to take some of the sting out of a tough task.

By David Carey
President, Portelligent




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