Weird component found in cheaply made glucose meter. - Page 1
Forum section: electronics / general

author: Razor512
author_rank: Regular Contributor
timestamp: December 27, 2013, 09:56:22 pm
content: I found an Exactech blood glucose meter in a "free" box at a flea market, and the device felt so cheaply made that I just had to take it, and see what is inside. (feels like one of those really cheap single line calculators that you would get in a cereal box back in the 1990'sAfter taking it apart, I noticed what seems to be a crystal oscillator, but it has a window on it. Why would the part need a window?Image of the PCBhttp://farm6.staticflickr.com/5487/11591441303_d8421dd313_o.jpgPart of the second PCB broke while flipping it over, the strength of the 6 leads on the right side when bending the board over, was enough to snap it in half(0.70 mm thick)View of entire PCB (non broken):http://farm8.staticflickr.com/7445/11591441683_86b23b4a45_o.jpg

author: Rudane
author_rank: Regular Contributor
timestamp: December 28, 2013, 12:42:30 am
content: That's weird. You're right, the piece inside looks like a crystal. Check out the wikipedia article on crystal oscillators and you'll likely see a picture of the inside. Two things strike me as odd. First is that the two ends (both on the left) that I would call the pins of the crystal seem to be connected together from this angle. Second is the lack of a second capacitor. I've only seen the two capacitor oscillator, since you need a full 360 degree phase shift for the instability criterion of an oscillator. Two caps give 90 each, and the inverter inside the chip is another 180. It's been a while but I think that's right.Edit: I've thought about it, and where is the actual sensor? I think this may be the glucose sensor. Was there a covering for the sensor window that was part of the plastic case?

author: Stonent
author_rank: Super Contributor
timestamp: December 28, 2013, 01:30:49 am
content: From what I've seen there is no actual sensor, just a few metal tabs that touch the strip. The strip itself has a chemical in it that makes a measurable electrical change that the metal tabs can detect.

author: Razor512
author_rank: Regular Contributor
timestamp: December 28, 2013, 02:08:15 am
content: for a glucose meter, the test strip does a lot of the work (thats why those strips are so expensive). The test strip eventually touches a few contacts on the PCB, and the device does something to them (not sure what) to actually calculate the blood glucose.They didn't have any test strips there so I am not sure 100% of how it works, but I did find an image on a google image search(really wanted to get a hold of a test strip so I could take it apart, and get photos of it also.As for the PCB, I was mainly wondering why a crystal oscillator would need a glass window? I have always seen them as being sealed inside of a can or something.

author: hiddensoul
author_rank: Regular Contributor
timestamp: December 28, 2013, 02:32:46 am
content: Yep is certainly a crystallook at the high res photo you can see the Freq of 524.288Khz stamped on it

author: edpalmer42
author_rank: Super Contributor
timestamp: December 28, 2013, 03:49:06 am
content: The dark 'arrows' above and below the numbers are a dead giveaway that the crystal is fromwww.statek.com. That's their logo. They often use that style of case.Ed

author: hiddensoul
author_rank: Regular Contributor
timestamp: December 28, 2013, 05:08:58 am
content: Quote from: edpalmer42 on December 28, 2013, 03:49:06 amYeah I just went looking around the site and the glass lid package is for high shock applications, I am guessing a portable blood meter would be dropped a lot and carted around in a bag or pocket. Also the glass lid is more then likely for visual inspection for physical damage from excessive G loads as a guess

author: Joule Thief
author_rank: Regular Contributor
timestamp: December 28, 2013, 05:25:04 am
content: Quote from: Razor512 on December 28, 2013, 02:08:15 amA link for the explaination of how the sensor strips function.https://wiki.engr.illinois.edu/pages/viewpage.action?pageId=44729985http://cache.freescale.com/files/microcontrollers/doc/app_note/AN4364.pdf

author: Joule Thief
author_rank: Regular Contributor
timestamp: December 28, 2013, 05:28:55 am
content: Quote from: hiddensoul on December 28, 2013, 05:08:58 amdiabetes will result in loss of sensation in your extremities - dropping the meter while inserting strips is to be expected