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Need advice on scanning 2.4ghz with Arduino
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Need advice on scanning 2.4ghz with Arduino

by Molten Fungus on Fri Feb 01, 2013 3:46 pm

Overview
------------
My daughter was recently diagnosed as a type 1 diabetic, and recently acquired a DexCom Continous Glucose Monitor (CGM). The CGM consists of a sensor, transmitter and receiver. According to their Spec, they broadcast in the 2.4Ghz range and even specify packet sizes. Though the monitoring tech is awesome, the interface is pretty sad. For example, I would like to be able to use a smartphone instead of that handheld device they sell, and if possible, send a text to either mine or my wife's cell phone (I would need to get up to speed on writing an app..but that's not the issue) when she's in school. Also, instead of having a phone and this receiver, in my mind it should be one device. ( I have more ideas that would make life much easier, but this is an overview)

So..being an Arduino fan (mega and uno with Sainsmart stuff), I was wondering how to get started with the above project. I've already figured out how to decipher IR with some of the papers on this site, and I'm wondering if this is something do-able, and if so, what hardware would I need to get started.
Basically, to get started, I'd like to see the packets coming in from the transmitter and try to figure out what's going on.. I don't have protocol specifications.

If I'm just being naive, let me know.

Thanks ahead of time.
Molten Fungus
 
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Re: Need advice on scanning 2.4ghz with Arduino

by janekm on Sat Feb 02, 2013 10:37 am

Unfortunately there is not as much protocol standardisation at 2.4GHz as with IR, so you don't have a realistic chance of decoding the signal without knowing what protocol is used.
A good start is usually taking apart the device and figuring out what radio chip is used (I'm not recommending that in this case as it's a medical device).
Even if you know the chip, many chips support multiple encodings and protocols. And if you're really unlucky they may be using an encrypted link too.
Here's a great blog about reverse engineering radio protocols: http://travisgoodspeed.blogspot.co.uk/?m=1
janekm
 
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Re: Need advice on scanning 2.4ghz with Arduino

by Molten Fungus on Tue Feb 05, 2013 1:09 pm

Thanks..
I'm scanning the blog now..There's no way I would even attempt at opening up the transmitter..

The actual packet being transmitted is 240 bytes, 6 of them being the transmitter ID..
The information (I'm guessing) is some numerical value, which is used by the receiver where it does all it's calculations..
well.anyway...it's a challenge..

Thanks for the info.. I just needed some quick path to get started..
Really do appreciate the response.
Molten Fungus
 
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Re: Need advice on scanning 2.4ghz with Arduino

by zorch on Sat Dec 21, 2013 2:00 pm

What about accessing the USB port on the Dexcom G4 Receiver instead? Could one use a USB Host Shield along with insights from work such as https://github.com/compbrain/dexcom_reader to develop a reader? Then in a perfect world one would couple it with something like an RFduino to send the data to a Bluetooth Low Energy capable smartphone. Voila, mobile remote monitoring for your daughter.
zorch
 
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Re: Need advice on scanning 2.4ghz with Arduino

by polydon68 on Wed Dec 25, 2013 10:21 pm

I second the notion of utilizing the USB port. I'm not a professional programmer by any means.
What most parents want is a remote monitor for their child's Dexcom overnight. This is the scariest
time for us and the reason that most parents of type 1 kids are sleep deprived because of all the nights
they wake to check blood sugars.

Wouldn't it be a fairly straightforward project to poll the serial (USB) port on the Dexcom using an Arduino,
and have that data sent by XBee to another Arduino module with XBee and an LCD + alarm?

Just having the numbers by the bedside and perhaps a low alarm would mean so very much to MANY
tired and worried parents.

(once the data is on the first Arduino other options are possible, WIFI, Ethernet, data sent to a server and posted
as HTML- accessible worldwide, etc)

This has become my winter project, but I'm no programmer (I'm a scientist who has only programmed when forced to.)

Glad that there are better minds working on this. Please keep it up!
polydon68
 
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Re: Need advice on scanning 2.4ghz with Arduino

by osazuwa on Wed Feb 26, 2014 7:03 pm

Has anyone made progress on this item? I am interested in hacking the monitor as well. It will take too long for an actual smartphone syncing or bluetooth enabled product to come to market.
osazuwa
 
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Re: Need advice on scanning 2.4ghz with Arduino

by adrien on Tue Apr 29, 2014 1:23 am

there is quite a bit of good code around in github regarding accessing the Dexcom USB interface. In fact I wrote a plugin for WinGate to poll it for my son and push it into WinGate's event processing system (which I configured to email/SMS me). I plan to make this freely available, and there's a free WinGate license you could use as well - it needs a windows PC though, so that's fine for overnight, but not portable enough for school etc. Check out github projects called "blood shepherd". Also Don Browne has been very helpful (gave me checksum and some other code in C# which I ported to C++).

The radio transmissions from the transmitter are also documented in a couple of places. I know of people who used a Texas Instruments CC2511EMK to read the packets. They use MSK modulation, and use 4 channels (transmit sequentially on the 4, presumably for reliability). Look up the FCC documents for certification of the transmitter, they contain more information about the transmitter. Also even the dexcom manual has information in it, including the frequencies. From what I understand it uses SimplicIT packet format / stack. You can spy on it with TI SmartRF packet sniffer.
adrien
 
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Re: Need advice on scanning 2.4ghz with Arduino

by zorch on Thu May 01, 2014 10:55 pm

You could build an open hardware / open software Babel Fish for pumps, CGM's, and activity devices the size of a smartphone, for $100.

http://www.microduino.cc/wiki/index.php?title=Main_Page

916MHz
BLE
stepper motor
USB Host
LiPo charger
CPUs in various sizes
SD card

Here are some repos for accessing devices via USB:

https://github.com/rnpenguin
https://github.com/hackingtype1
https://github.com/bewest?tab=repositories
zorch
 
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Re: Need advice on scanning 2.4ghz with Arduino

by dhconsult on Thu Jul 17, 2014 12:38 pm

In case this is a post that other's are still following, there is a way to get the Dexcom readings out of the Dexcom G4 receiver via the USB port. It's a bit involved but completely possible and there are actually a bunch of people who have now done it with a combined group effort to make it happen. Check it out here:

http://imgur.com/a/cxcGG?gallery

http://nightscout.github.io/

http://nightscout.github.io/posts/01-quickstart/
dhconsult
 
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