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

Andrew Errington erringtona at gmail.com
Sat Aug 29 05:10:22 BST 2020


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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