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

[Charles Manning]

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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