[chbot] CovidCard implementation - how expensive should it be to manufacture 1M of them?

[Charles Manning]

Thanks for that.

I hadn't seen a HID GATT profile. BLE has very limited data transfer rates
and a full  steam HID would not be possible. BT EDR can achieve 2 mbits/sec
data transfer, USB can achieve 10Mbiits/sec (full speed) and BLE can only
achieve 2kbytes/sec or so max due to the way most OSs throttle BLE.

Still, for any of this tracking style stuff you need a connectionless
protocol - not a connected protocol. For that BLE beaconing is the best and
was pretty much designed for this type of purpose.

The hassle with 100s of metres style tracking is that it really gives far
too many false positives,  Everyone driving past one of the isolation
hotels would have been close to a CV19 person. Get stuck in a traffic jam
or walk past and you've been "close" to them for 10 minutes.

While individual Wifi SSID and BT beacons have reasonable range (a couple
of hundred metres), the use of both RSSI and a number of MACs will cut the
location down to a smaller size (maybe 20 metres or less).






On Sat, Aug 29, 2020 at 4:10 PM Andrew Errington <erringtona at gmail.com>
wrote:

> Voila! Un clavier BLE:
>
>
> https://learn.adafruit.com/ble-hid-keyboard-buttons-with-circuitpython/overview
>
> But, I still maintain that tracking people's phones and then contact
> tracing the Infected is the easiest way, given that everybody* has a
> phone, and it's possible to track them to within a few 100 metres.
>
> Andrew
>
> * for appropriate values of 'everybody'
>
> On 29/08/2020, Charles Manning <cdhmanning at gmail.com> wrote:
> > BLE is nothing like "classic BT" and they really should not have called
> it
> > BT at all.
> >
> > These do not use HID profiles etc but use BLE comms instead.
> >
> > All that is needed is to transmit occasional (every few seconds)
> > advertising beacon messages and for the receivers to check for these. The
> > receiver then needs to record RSSIs (how close) and duration etc for
> > "contacts" that exceed whatever threshold.
> >
> > Unless you're making intimate physical contact, the rule of thumb seems
> to
> > be that you need to be closer than 2 metres for 15 minutes to transfer a
> > large enough "dose" of a virus to establish an effective infection. Just
> > walking past someone for a second or two is not enough.
> >
> > Devices like these can be very easily built using BLE single chip SOCs
> from
> > Nordic or Silabs or similar and can run for over a year on a single coin
> > cell.
> >
> > The biggest hassle is the logistics of rolling this out. (ie. design,
> > manufacture of millions and get them in use).
> >
> > Why not just record a "digital diary" using smart phones that pretty much
> > everyone has these days? Every minute or so, just record the 5 most
> > powerful Wifi MAC addresses. There are very few locations where there are
> > both people AND no Wifi. So what if you miss a few spots?
> >
> >
> >
> >
> > On Sat, Aug 29, 2020 at 3:28 PM Robin Gilks <robin at gilks.org> wrote:
> >
> >>
> >> >      *   broadcast once per minute its own ID and nothing else
> >>
> >> Do you think that is often enough? I would have thought closer to once
> >> per
> >> second otherwise you miss the very close contacts that don't last very
> >> long.
> >>
> >> Bluetooth Low Energy can beacon quite comfortably at this rate but the
> >> scanning takes more effort (and power) as there are 3 channels to check
> >> and they need to be continuously listened to (within the confines of the
> >> BLE frequency hopping) otherwise again you miss close contacts.
> >>
> >> Assuming just using RSSI to determine distance, orientation will affect
> >> the signal by up to at least 30dB but at least the transmit power can be
> >> turned right down as only 2m radius is of interest. Multiple reading
> >> averages will still have to be used due to signal strength fluctuations.
> >>
> >> It also tricky finding a cheap solution that can do both Central and
> >> Peripheral roles simultaneously.
> >>
> >> --
> >> Robin Gilks
> >>
> >>
> >>
> >>
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