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Dexcom Stelo teardown

A couple months ago, I decided to try out the Dexcom Stelo blood glucose biosensor to see what kind of near-realtime feedback about my blood glucose levels I could get (more about that in a future blog post, probably).

These are small plastic devices about 23 mm x 27 mm that are supposed to last about 15 days. After they’re spent, you take it off and replace it with a fresh sensor.

Dexcom Stelo blood glucose biosensor
Dexcom Stelo blood glucose biosensor

Naturally, I wanted to see what was in them so I took one of the spent sensors and got some x-rays of them.

For my first image, I x-rayed a spent Stelo using a regular radiographic unit at about 5x magnification, 80 kV, 1 mAs.

X-ray of a Stelo blood glucose biosensor. 80 kV, 1 mAs.

Decent enough image that shows what appears to be the battery (the round object), the Bluetooth antenna (the trace toward the top), the sensor wire (the straight horizontal wire near the middle) and some of the traces on the circuit board.

I wanted a better image so I used a mammography unit. 38 kV, 40 mAs with about 1.8x magnification.

X-ray image of an intact Dexcom Stelo blood glucose biosensor. Image was acquired using a Hologic Dimensions mammography unit, 38 kV, 40 mAs at 1.8x magnification.
X-ray image of an intact Dexcom Stelo blood glucose biosensor

Now we see the traces on the circuit board much clearer. The round object is definitely a battery, and there are signs of at least a couple of microchips.

Time to liberate the circuit board from the casing, which turned out to be a bit of work. It looks like the Stelo is built by injection molding (or some similar process) plastic around the PCB. With a process like that, these are definitely waterproof. After some work with a knife and cutters, I was able to liberate the board.

Printed circuit board extracted from a Dexcom Stelo blood glucose biosensor
Printed circuit board extracted from a Dexcom Stelo blood glucose biosensor

The battery turns out to be a CR1216 coin cell and occupies most of the back side of the device. The microchip on the right is marked N52832 and is a Nordic Semiconductors nRF52832 that takes care of the Bluetooth. It boasts some pretty impressive specs for such a small device. The small silver rectangular thing below and to the right of the nRF52832 is probably a crystal oscillator. It was marked with T320 MnKC.

The other chip is marked DCG7 (probably a custom designator, maybe standing for DexCom G7, their other continuous glucose meter), would likely be the brains of the device. The gold circles on the board are test points.

With the battery out of the way, an x-ray image of the PCB reveals much more detail.

X-ray image of the printed circuit board from a Dexcom Stelo blood glucose biosensor. Image was acquired using a Hologic Dimensions mammography unit, 38 kV, 40 mAs at 1.8x magnification.
X-ray image of the PCB from a Dexcom Stelo blood glucose biosensor

The BGA pads on the left side of the battery terminal would be for the nRF52832 chip while the QFN pads on the right side would be for the DCG7 chip. Aside from a bunch of other surface mount passive components, there’s not much else to the Stelo.

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Advent of Code 2024

Advent of Code is a fun set of Christmas themed programming puzzles that has been going on from December 1 through December 25 for the past 10 years now.

Advent of Code is an Advent calendar of small programming puzzles for a variety of skill levels that can be solved in any programming language you like.

Advent of Code/About

For 9 of those years, I’ve been following the puzzles and thinking “I should give these a shot”. For a variety of reasons, primarily lack of time, I never got around to doing them.

This year, I decided to tackle the Advent of Code 2024 puzzles. I chose to use PHP and Laravel Zero because it’s what I know.

The puzzles generally start out simple, and then become more complex as the days go on.

My programming skills are pretty rudimentary, so I had to spend a good amount of time thinking about how to go about solving each day’s puzzles. The easier puzzles I was able to solve, mostly using brute force methods. The more complicated puzzles I had to skip because they were beyond my current skill level.

I thoroughly enjoyed spending time working on this year’s Advent of Code puzzles and had a lot of fun. There were lots that I skipped, but I was honestly kind of surprised that I was able to solve as many as I did. The solutions were probably far from elegant, but they worked. If I get motivated enough again, I may go back and tackle some of the ones I skipped this year, or perhaps work on puzzles from previous years.

Advent of Code 2024 is over for the year, but all the puzzles are still there for this year and all the previous years. Anyone can go work on the puzzles they didn’t complete, or start from the beginning anytime they want.

The code I wrote for Advent of Code 2024 is over in my Github.

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Rescued slide rule case

While browsing around my local Habitat for Humanity ReStore a week or so ago, I came across a Pickett slide rule case sitting on one of the shelves. Got super excited, and then got super disappointed when it turned out to be just an empty case. It was priced at $10, which I decided was a little too high for just an empty case, so I decided to pass on it.

Fast forward to today, the case was still there on the shelf. With a 50% off holiday sale going on, I decided $5 wasn’t a terrible price for the empty case, so I bought it.

It’s a black case, worn but still in pretty decent shape. The Pickett logo is partly worn off but still readable. No other identifying marks on it though.

Front view of a Pickett slide rule case for a 12 inch slide rule
Back of aPickett slide rule case for a 12 inch slide rule
Side view of a Pickett slide rule case for a 12 inch slide rule

Now I need to find another Pickett slide rule to put in it.

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November garden update

It’s Thanksgiving day, the days are considerably shorter than they were a month ago, leaves are falling off some of the plants, but the jalapeno plants are still going strong.

A couple weeks ago I harvested almost 2kg of jalapenos, and there are still lots more left on the plants. I’ll wait a few more weeks to harvest those. Flowers keep popping up, and I’m finding new jalapenos growing just about every day.

1.89 kg of jalapenos in a large plastic container, freshly harvested from the garden

It’s been a good year for jalapenos.

The fig plants have become quite tall, and are still continuing to fruit even though a lot of the leaves have fallen off. I’ve observed that if I lop off a branch near where a leaf had grown, more leaves start sprouting from that leaf bud. Seems like this will be helpful for managing the height of the fig trees.

The last remaining butternut squash plant keeps producing squashes. Most of them ended up failing, but there’s one small one that’s hung on and may be ready to pick in a month or two if the cold doesn’t get it first.

A failed squash
A failed butternut squash
Butternut squash sitting in the raised bed
Last butternut squash of the season

Weather is supposed to be turning cold for the next few days, with lows just below 0°C and freeze watches.

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October garden update

The larger and older leaves on the fig plants have started to dry up and fall off, which to me is a sign of fall. The plants are also sprouting new leaves at the same time. Figs are slowly ripening, and I’ve picked a few of them already.

The jalapeno plants continue to do pretty well, and I’ve already harvested several pounds of jalapenos. Looks like there’s easily several more pounds waiting to be harvested. I’m trying to resist the temptation to pick a bunch of them and letting them stay on the plant to turn red.

Three small red jalapenos and a small fig.
Three small red jalapenos and a small fig.

I thought the butternut squashes were done for, but there’s one plant that still seems to be hanging on, and has produced a few more butternut squashes that might get me a small late fall crop.

A small green growing butternut squash
A small green growing butternut squash
A small green growing butternut squash

A bunch of these grass/weed plants in the two empty beds that I’ve been letting grow wild put out a bunch of little flowers that have been attracting a lot of bees, butterflies and moths. It’s fun and relaxing watching them buzz and flit from flower to flower.

Wildflowers growing in an empty raised bed
Wildflowers growing in an empty raised bed

The little sweetgum sapling that sprouted up next to the jalapenos made me wonder what other tree-type thing I could get to grow in the garden. It’s the time of year when the live oaks around work drop acorns, so I picked up a few, buried some in one of the raised beds, and put a few more into an empty pot.

No idea if any of them will sprout, but we’ll see. It will be a nice surprise if any of them grow.