What you need
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Once you rip off the sticking plaster (you can simply do this with your hand), you can see the front of the sensor from one side. A white cover with the hub for the needle in the center. On the other side, one can already see the board under the transparent plastic layer. Be careful with the needle!
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The edge can be ground with a Dremel rotary tool. With the help of some pliers, one can peel off the plastic and with a bit of fine feeling one can take out the board.
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One can see the contacts for the needle on the transparent plastic. They are also clearly visible on the board.
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On the backside of the board, one can just see some unlabeled contacts.
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There are two antennas next to the big round battery. One is made of ceramics for Bluetooth and another one wrapped in Kapton tape that is probably used for the NFC transmission.
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Two chips form the core. The bigger one is a RF430, and it is responsible for RFID. The smaller one is an EM9304 Bluetooth chip.
Hello, Top left is antenna, top right is a thermistor, a temperature sensor.
Here is a photo I took of the freestyle v1 I took 5 years ago:
https://i.imgur.com/e3jAipX.jpg
Here the antenna is a trace around the PCB.
You can open the unit up by simply driving a thin blade in between the colourless and white parts. Perhaps a design change since this teardown has meant tool-free and glue free assembly.
The one I just opened up says "Rev C" on the reverse of the PCB, whereas this teardown is for a "Rev B"
What exactly is the point of this teardown ? apart from showing the internal pictures, because :
- You cannot use the MCU in any way as it's code locked ! yes we looked into trying to reuse it for really anyting else because of the 14bit ADC, but no chance.
- when you dig into the Abbot workflow of the Freestyle2 you will clearly realize the impossibility to medically protect a piercing needle into your skin from a ripped apart device, the Battery will not last more than 4 to 6 days longer than it's intended consumption , so even trying to use it as a temperature sensor is wortless.
- as pointed out by @gavinhodgson its simpler to open it by just prying the side of the disc (on ALL Rev's)
- actually this one should be first: How do you plan to reset the device to factory new so that the reader can activate it (if you do manage to assure a safe medical pierce from the suck in needle) ?
Afterall maybe you do have some trick up your sleeve to get this reset after it's intended use, so spit it out please.
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18 Comments
The device in the Kapton tape is a temperature sensor.
Thanks for the comment!
But do you know where the NFC antenna is then?
Nathalie -
Is in the perimeter of the PCB, under the PCB, a trace that rounds it. you can see a grey circle in its circumference.
I’m looking at a 14 day Libre board and the antenna is clearly 3 parallel traces that are around the perimeter of the pc board. Looking at your pictures I would say that it appears they are on an inner layer of the board. That dark circle is where they are. And, looking at the backside of the board I see a couple of vias that allow them to connect to that inner layer. The antenna pins of the RF430 are pins 1 and 2. There is a dot above and to the left of the RF430 marking that indicates where pin 1 is. I appreciate you doing this teardown. I’m just now wearing my first Libre 2 sensor. Search the TI web site for RF430FRL152H to find the data sheet on the processor part.
Great teardown.
Stuart Diamond is very likely correct - the NFC antenna is almost certainly the dark ring around the edge of the board (on the opposite side of PCB from what you see in the photograph). NFC will need to be a coil.
What battery did you find? Can you share any markings or photos of it? Thanks!
sr626sw button cell
In the v1 sensor there was an NFC antenna with three circles of circuit path. I can’t recognize those in the “darker” ring on the new sensor, though. The ceramic antenna seems to be the BT-chips antenna. The supposed “antenna in capton tape” is most likely a thermal sensor. Though I am not an expert in this field, I am pretty sure about that.
I've got six new and unused FreeStyle Libre 2 (USA) sensors expiring (per unopened packaging) at the end of this month. An idea is to set up a new Libre 2 Bluetooth reader with a backdate of a few months so that I don't waste these sensors. My assumption is since the reader isn't internet connected, backdating isn't a problem, but I’m worried about the sensors possibly having a clock within them. Any idea if this hack would work?
My guess would be expiration is linked to the shelf-life of the battery, so your mileage may vary.
ABR -
CGM monitors are used to track blood glucose levels in patients with diabetes. These monitors have sensors that connect to a small device worn on the body (a patch or a reader) and use a transmitter to send data from the sensor to the reader.
Lo más interesante de este dispositivo es el sensor de Glucosa, que casi seguro debe ser resistivos, dado que este IC NO es especial como imaginé, antes de abrirlo. Cuando vi que tenía un chip sencillo RFid, ya está, dije toda la magia está en el sensor, el resto es muy común...
Si, creo tambien que es el sensor de Glucosa que vale.
Is it possible to measure Gluc. levels (only) over R? (...what about salts etc in the plasma then?) Not sure if it can be done, but I could imagine the sensor measures some frequency-response-patterns. (e.g. send various freq. in the tissue, and measure each's "response"(?) Also because the tracks to the CPU seem to be shielded. Sort of, because doubled and that could be to compensate for noise / magnetic fields etc (track "up" cancels out noise from track "down", or at least one can subtract the part of signal that's noise, since they'll mostly receive equal amounts of distortion, being close to each other. Think RS485 has a similar principle to protect against noise.
Do these sensors expire as Amerique_du_Nord describes? (I'm in EU) I mean, without activation? I think the sensor may not even be calendar-"knowing", but just counts 14 days starting when activated.
Curious which part is being destoyed (fuse burnt?) when due. Is it in the RF430?
The "RF430" chip is made by Texas Instruments: https://www.ti.com/lit/ds/symlink/rf430f... and is an NFC transponder
The "EM9304" is by EM Microelectronic and as you say, is a BLE 5.0 SOC https://www.emmicroelectronic.com/produc...
The coin cell is an SR626W
More of a destructive disassemble than a teardown.
On the needle side there are clearly clips that hold the center to the back cover. I'll let you know how to undo them when I do my teardown.
More pictures of the sensor array.
https://www.dropbox.com/s/7zywkdi594o006...
This design is very simple. All cheap off-the-shelf parts except for the needle/probe. A chemical reaction produces a current, and the RF430 measures it. The needle eventually runs out of chemicals and stops producing an accurate current, which is why the devices last weeks, not years. Unfortunately, this means the devices are not really repairable, hackable, or upgradable in any meaningful way. The expiration date might refer to the needle chemical shelf life, as well as the battery, since it appears to be always-on from the factory.
The Battery says:
SR626W
0%Hs
SEIZAIKEN JAPAN
I wish they were easier to remove from the unit. I’d love to find a way to reuse the battery or give them to someone to use for a hearing aid- anything before it goes to the landfill.
You don’t need a dremel if you don’t want to keep the circuit board intact. I cut it in half with my tin snips!
