Category: Hobbies

Things I do for fun

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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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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.

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A jalapeno harvest

Picked a few jalapenos today. There are a bunch of them on the jalapeno plants in various stages of growth. These were a pretty decent size and colour and looked ready for picking.

Also spotted a new butternut squash starting to grow. Hopefully this one sticks around.

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September garden progress

The jalapeno plants seem to be doing pretty well, and are recovering nicely after getting solidly munched by the tobacco hornworms.

Haven’t spotted any more hornworms on them recently, but there was this little green lizard hanging out on a jalapeno. Hope he’s finding lots of bugs to eat.

Looks like there will be a bunch of jalapenos to harvest in a few more weeks.

Jalapenos growing in the garden
Jalapenos growing in the garden

The butternut squash plants have been struggling lately and it looks like there might be just one plant left that’s still sending out runners.

Butternut squash plant in the raised bed

There have been a few attempted new butternut squashes, but they all ended up shrivelling up before getting very large. Might be time to pull the plug on this batch.

Some shriveling up butternut squashes

This mystery plant started growing in the bed next to the jalapenos a few months ago. I was curious to see what it would be, so I let it grow. The leaves look like maple leaves except for the serrated edges so I don’t think it’s a maple (I’d be very surprised if it was).

Mystery plant growing in the raised bed. Possibly a sweetgum tree.
Mystery plant growing in the raised bed. Possibly a sweetgum tree.

A Google Lens image search suggests this is a sweetgum tree, which seems plausible. I know there are a few of these growing in other yards around here

Late in July, the ornamental cherry tree out in the front yard surprised us with a big display of leaves on the lower branches. Then Tropical Storm Debby came, dumped a ton of rain on us. After that, all of the leaves shriveled up and dried up. I was starting to think that maybe all the water drowned the tree and that it was done for.

Dead leaves on the ornamental cherry tree
Dried up leaves on a drowned tree

Last week, the tree surprised me with some new leaf growth. Seems like the little tree might recover after all.

New leaf growth on the ornamental cherry tree
New leaf growth on the ornamental cherry tree
New leaf growth on the ornamental cherry tree
New leaf growth on the ornamental cherry tree

The fig plants continue to do well, and there are a bunch of figs now. They’re still pretty hard, and seems like it will be a few more months before any might be ready for harvesting.