These are chat archives for nightscout/intend-to-bolus

6th
Nov 2018
PieterGit
@PieterGit
Nov 06 2018 06:43

@cluckj @alimhassam or other Dexcom G5/G6 users.
I have a another question on the Dexcom G6. This time on the bluetooth protocol.
Does anybody know how much a data a Dexcom G6 transmitter transmits over Bluetooth LE?
Does it only transfer the bloodglucose in a packet every 5 minutes, or does it have a
much shorter advertising interval to let the phone/rig know the transmitter is still there.
According to the Dexcom docs the Dexcom G4 only sends 224 bits per packet, ands sends
4.48ms data every 5 minutes on the 4 2.4Ghz TX-frequencies.

I was wondering about how much data the Dexcom G6 transmits and if it uses a heartbeat.
I can't find any data in the official docs. Does anybody know or has
checked the bluetooth LE traffic of the Dexcom G6?

Name
@orbarya
Nov 06 2018 07:14
@yeagerm OK thank you!
alimhassam
@alimhassam
Nov 06 2018 11:10
@PieterGit my understanding is that the g5/g6 acts as a ble service. It wakes up every 5 min about and you can request different amounts/type of data during a small window. I'm not sure what's the maximum.
alimhassam
@alimhassam
Nov 06 2018 11:17
@thebookins might be able to answer better on @PieterGit g5 protocol/advertising window question above. It might also help if we had a bit more context around your question @PieterGit
You could in theory get almost no data or request 3h worth of glucose and maybe a predictive curve, As well as battery status etc in that interval every 5 min. I think that's probably more data than the g4.
Martin Haeberli
@mhaeberli
Nov 06 2018 15:50
@alimhassam based on empirical experience, for some reason in our use of the G6 the ‘backfill’ of data one could get with the G5 doesn’t seem to be happening (or not as reliably and well)
PieterGit
@PieterGit
Nov 06 2018 19:17
@mhaeberli if you can test ecc1/nightscout for token based authentication please do. can't test atm because of battery of G4 transmitter died :worried:
Martin Haeberli
@mhaeberli
Nov 06 2018 19:26
@PieterGit ok thx; not sure I can help. ours uses a G6 (only via share). But I have a test pump and rig of my own (CGM data only via share). If that’s a viable test configuration, I can play with it on my test platform.
PieterGit
@PieterGit
Nov 06 2018 19:28
@alimhassam thanks for your answer. To clarify my CGM BLE question for you and @thebookins. Because of the dead G4 battery I'm considering whether this is the moment to switch from Dexcom G4 to G6. My PWD is a bit (too) worried about GSM/WiFi/BLE/pump-rig comms health risks (radiation). Especially for the CGM sensor because it's worn on the body. So I tried to look up and calculate the difference in transmit power and amount of data sent of the G4 and G6 CGM but I couldn't find the answer in the technical specs and I'm curious about the communication that is used.The G6 has a transmitting power of 1.0 mW EIRP which is less than the 1,25 mW EIRP of the G4. On the contrary I assume the BLE does much more advertising and just like you say the G6 probaby sends more data (but faster, 1 Mbps vs 49.987 Kbit/sec) from the rig to the mobile phone or rig that is used. I was wondering if people have sniffed the BLE comms of a G6 and can tell me what is being transmitted between G6 transmitter and rig, or G6 trasnmitter and phone.
PieterGit
@PieterGit
Nov 06 2018 19:36
@mhaeberli the @ecc1 libraries also download the CGM data from Nightscout and merge it from a G4 connected to the rig. If I'm right your uploading follows this path: G6 Transmitter -> Mobile phone -> Dexcom -> share2nightscout bridge -> Nightscout -> rig . I assume CGM=G4-go also should work in this case, but others probably correct me if I'm wrong on that one. The part that has changed is that the ecc1/nightscout now supports Nightscout token based authentication. I tested it, but I wasn't able to test the latest changes of @ecc1 because of my broken G4 transmitter.
Martin Haeberli
@mhaeberli
Nov 06 2018 19:54
ok thx… I’ll try to take a look later.

getting this message:

./ccprog -p 19,7,36 erase
Using pins: DC=19, DD=7, RESET=36
Erasing chip.
This code is only tested on CC1110. Unsupported chip id = 0x00.
Chip erase failed.

(on a brand new Explorer, as well as an older Explorer.) (how) am I holding it wrong? I’m beginning to suspect the Edison proper. Unless maybe the new Explorer uses a different chip?

Martin Haeberli
@mhaeberli
Nov 06 2018 20:12
(Ok - found that a different Edison CAN erase and program - so it’s the Edison, stupid!)
Scott Leibrand
@scottleibrand
Nov 06 2018 21:36
@PieterGit you might want to look at the amount of 2.4GHz radiation emitted from a microwave oven, and compare how far you'd have to be away from the nearest microwave to get down to the level of emissions of a BLE transmitter...
PieterGit
@PieterGit
Nov 06 2018 22:56
@scottleibrand I agree that the amount of radiation is very low. Point is, that the G4 manual is clear about the radiation, and the G6 manual does not give enough information to calculate it (or to compare it to a microwave oven radiation). I would like to understand the magnitude and thus would like to know how the bluetooht protocol between G6 and rig or phone works
Paul Dickens
@thebookins
Nov 06 2018 22:57
@PieterGit As @alimhassam said the amount of data that is transmitted can vary, depending on what the controller asks for. At a minimum the transmitter advertises its presence every 5 minutes with an 'advertising packet'. Then there is a service discovery phase (bit hazy on the details here) where the BLE central can inquire of the peripheral what services and characteristics are available. Then there is an authentication step, where the central and peripheral exchange some messages derived from the transmitter ID (to prevent snooping by people who don't know the ID). If that passes, there is then a pairing phase (see here for details) where the central and peripheral exchange keys to set up an encrypted connection. After all this, the central (1) asks the peripheral for its current time (2) sends any pending commands (start / stop / calibrate), (3) asks for the current glucose, (4) asks for the latest calibration and (5) may ask for 3 hours of backfill data.
I may have the output of some BLE sniffing I can send you if interested.
PieterGit
@PieterGit
Nov 06 2018 23:00
@thebookins yes, please PM them. Since it's likely that I will switch to G6, it's good to understand the low level protocol more than I do now. Thanks for the answer
Scott Leibrand
@scottleibrand
Nov 06 2018 23:00
I think you can ignore the duty cycle and just look at the maximum transmit power, and you'll still find that having a microwave in the house exposes you to more 2.4GHz radiation than any BLE or wifi devices
and of course, 2.4GHz radiation is used in a microwave because that's the frequency that water absorbs best. so the only reason to worry about 2.4GHz is if the quantity of radiation is sufficient to heat up tissues with poor circulation (like eyeballs), which < 1W transmissions certainly can't do.
Eric
@ecc1
Nov 06 2018 23:23
@thebookins if you find the BLE captures, please PM them to me too. I'm working (off and on) on some Go code to talk to G5/G6 sensors