EE Times Under The Hood - October 8, 2007 - (Page 50) under the hood: DIGITAL HOME 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 factor of data entry coding, the smart disk provides immediate, error-free calibration data. The Breeze is easy to use. 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 the blood sample is applied, the reading is ready to be taken. I didn’t buy a disk, so I can’t speak to the particulars inside the 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 circuit—located on the flip door that houses the disk—makes contact via 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 appa- www.eetimes.com • www.techonline.com IN BRIEF Personal medical test devices have come a long way in the last 20 years. The Ascensia Breeze is an example of the current state of the art in blood glucose monitoring (BGM), where a fairly low cost and physically small size allow for easy portability and more affordability. The electronics content is fairly simple but quite special, custom-made for the job at hand. ratus 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. 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 Component focus Silicon content rules the roost in the Breeze 2, but as with virtually any system, there’s usually a little bit more offered to produce a functional product, and the Breeze is no exception. Along with a couple of oscillators, two dozen passives, and a piezoelectric buzzer from Ningbo East Electronics, interconnect is key. A carbon-silver mylar flex circuit is used with a carbonsilicone-matrix Zebra connector to interface the meter to the special test sample cartridge for reading lot-specific coding information.This same flex technology is likely used in the dashboard of your car, among other places, providing a low-cost, high-reliability connection where neither currents nor interconnect density are high. A headphone jack-style connector is also present in the Breeze 2, providing a data port for downloading test history to a personal computer, not to mention an accessory sales opportunity with the special data cable. 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 μPD78F0338GC microcontroller. No A/D converter from the ASIC is obvious at the die level, so it seems plausible that signal conversion takes place in the NEC part’s internal A/D, where it can be manipulated to a displayed glucose level on the Breeze’s segment LCD. The LCD is driven directly by the microcontroller, which also handles the button input. Similarly, the NEC device is used to interface to the product’s headphonestyle connector, which implements a data port to allow the unit’s 100-reading memory to be downloaded for analysis on a host PC. A 4-kbyte 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. ■ 50 Electronic Engineering Times, TechOnline | October 8, 2007 http://www.eetimes.com http://www.techonline.com
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