siliconchip.com.au Australia’s electronics magazine May 2019 11
SCThe first version of the NBN, the Fi-
bre to the Home (FTTH) system, could
be fitted with a battery back-up power
supply giving about 8-12 hours bat-
tery operation, and was also consid-
ered reliable.
However, that all changed with the
introduction of the Fibre to the Node
(FTTN) and more recently the Hybrid
Fibre Coax (HFC) systems.
These two NBN systems use up-
stream equipment to convert from the
fibre network to either the customers’
copper or coax access technology, and
that equipment does not have battery
back-up.
The latest system, Fibre to the Curb
(FTTC), is a much better option as the
node in the street is back-powered
from the customer’s premises, and this
power could be battery-backed. Alas,
it has all come too late and FTTN and
HFC will have the majority of cus-
tomers.
Since the introduction of the NBN,
our industry group has been working
with NBN Co and the Retail Service
Providers to ensure a smooth and un-
interrupted transition for profession-
ally monitored medical alarm users to
the NBN. A federally funded scheme
was introduced to swap-over all PSTN
based monitored medical alarms in
NBN service areas with 3G wireless
alarms.
It could be argued that moving to
3G wireless was merely swapping one
set of risks for another, so most pro-
fessionally-monitored medical alarms
now have the capacity for dual con-
nectivity. They can make emergency
calls over both the NBN voice service
and the 3G mobile wireless service.
Clients with professionally 24/
monitored medical alarms can be con-
fident that their alarm service is reli-
able and will always be professionally
maintained.
The situation with non-monitored
medical alarms is more confusing. Be-
cause non-monitored medical alarms
rely on family and friends to receive
all the calls for assistance, and also
to test and maintain the alarm equip-
ment, they do not have the same de-
gree of professional support.
Recently, the federally funded alarm
upgrade scheme was extended to non-
monitored medical alarms, and some
users with PSTN based non-moni-
tored medical alarms have chosen to
upgrade to a 3G wireless alarm at a
lower cost.
There are also some 3G alarm pen-
dants/trackers being sold, which are
basically a mobile phone module and a
GPS receiver in a small housing. These
alarms have the advantage of working
outside the home and can show the lo-
cation of a person needing help on a re-
sponder’s smartphone. They also make
voice calls, so the responder can speak
directly to the person needing help.
Their disadvantage is that they rely
solely on mobile phone network cov-
erage, they need to be recharged eve-
ry day or two, and again, they do not
have the same degree of support as a
monitored alarm.
Note that some mobile devices, in-
cluding some new 4G non-monitored
medical alarms, are being marketed
as “future proof” 4G devices, even
though they can’t make voice calls over
Voice over LTE (VoLTE). Such 4G de-
vices can only make voice calls over
3G and, even though they are market-
ed as 4G devices, their voice function
will not work when the 3G networks
are closed down.
If you, or a member of your family,
are considering purchasing a medical
alarm I strongly suggest you take some
time to research the options and con-
sider the importance of a professional-
ly monitored and maintained service.
Phil Wait,
Neutral Bay, NSW.
Response: we still don’t understand
how 3G/4G provides sufficient redun-
dancy to be a useful backup for the
NBN for safety-of-life systems, as it
seems that both can go down within
hours of a widespread power failure.
And extended power failures are a
fairly common result of natural dis-
asters like fires, floods and cyclones.Shaded pole motor speed controller
thumbs up
I’ve just built the fan speed control-
ler for shaded pole motors from the
March 2014 issue.
Over time I had tried different
‘phase-controlled’ speed controllers in
Diac or Triac form, all of which made
the motor growl at lower speeds.
The concept of using a FET as a vari-
able resistor inside a rectifier to main-
tain AC in the external circuit was
inspired. At last, I have a speed con-
troller that can make a fan produce a
gentle breeze without any motor noise.
Thanks, Silicon chip!
E. McAndrew,
Capel, WA.For Wholesale prices
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