8 Silicon chip Australia’s electronics magazine siliconchip.com.au
For houses near the sea, in low ly-
ing areas, it’s possible for water pipes
to take a noticeable share of the return
path to the substation. It’s only dan-
gerous if there’s an inadequate return
path for a given load.
The 11-year-old girl received that se-
vere electric shock because the neutral
conductor was open circuit, probably
due to corrosion at the incoming con-
nection to the house.
The WireAlert could have detected
the unusually high source impedance
and warned the family.
Paul Smith,
King Creek, NSW.
Comment: that device is also known
as the “CablePI”. Bizarrely, it is the
subject of a safety recall as some units
are at risk of overheating and catching
fire! They only appear to be available
(at no cost) to people living in Tasma-
nia via TasNetworks.GPS Clock stopping may be due to
voltage sag
Regarding the letter on page 110 of
the January issue titled “GPS Clock
stops at five minutes to 12”, I built the
version of the clock published in the
March 2009 issue and had the same
problem on numerous occasions.
I was sure that it was not due to loss
of GPS signal (later proven correct), but
fresh batteries would get it going every
time no matter how good the installed
ones were. I tried cleaning the battery
connections very thoroughly but the
fault persisted.
Fifty years as an electronics tech has
taught me to first eliminate the power
supply as the problem. So I soldered
together two D cells and ran wires to
the PCB. MAGIC! That was in March
2016, coming up for three years and
not one failure since.Could it be AA cells drop voltage
under some load conditions and the
GPS module suffers a loss of power
which the program sees as a loss of
signal? The two D cells still measure
2.9V. And the clock is very accurate.
Timothy Ball,
Kogarah, NSW.
Response: that’s interesting, thank
you. You are right that a drop in volt-
age could explain it, but we wonder
why it isn’t a widespread problem.
Perhaps you are both using GPS
modules that draw more current than
the ones used in the original design.
Or perhaps the AA cells you’re using
have a higher impedance than usual.Serviceman story helped reader
with repair
I recently read the Serviceman’s
Log entry from J. W. of Hillarys, WA
regarding the repair on his Yamaha
receiver (September 2018, pages 66 &
67). This piqued my interest as I had
just received ours back from a tech
who had no luck fixing it.
I took the power board to a mate who
can test capacitors, and sure enough,
the same capacitor that J. W. found
faulty was well down in its rating. I
quickly purchased a replacement from
Jaycar and we are back in business. I
had been very close to dumping the
stereo, which is a shame as it’s a qual-
ity unit, despite being pre-HDMI.
This repair saved us the cost of re-
placing it, which would have been
substantial, but even better, it stopped
more e-waste from being created.
Thanks to J. W. for writing up his fix.
Serviceman’s Log and Mailbag are
my two favourite sections of the mag-
azine. I am looking forward to more.
Matt Agnew,
Christchurch, New Zealand.The sound through a sensitive rock-
ing armature insert earphone, such as
an STC 4T, is not ear-shattering. But
the program from some stations can
be clearly heard from about 1m away
from the earphone.
It would be great if you could de-
sign a crystal set around this device,
especially if Jaycar or Altronics could
produce a kit for it.
It has been quite some time since
you last published a project of this na-
ture. Perhaps you could publish one
more design while we still have an AM
radio band left!
Austin Hellier,
New Farm, Qld.
Significant differences between
BWD 216 and 216A
I found the article by Ian Batty about
the BWD 216A hybrid bench power
supply in the February 2019 issue
(siliconchip.com.au/Article/11419)
very interesting. I have a BWD 216,
serial number 12322. It is based on
the LM723 voltage regulator IC and
its circuit is very different from that of
the 216A published in the magazine.
Until I read the article, I had no idea
that the design changed so much be-
tween the 216 and 216A.
John Eggington,
Upwey, Vic.
Device for detecting
Neutral fault hazard
I refer to Dr David Maddison’s letter
about the electric shock hazard from
water taps, on page 12 of your Febru-
ary 2019 issue. There was a gadget, de-
veloped by Tasmanian Networks Pty
Ltd, that would make a loud sound
if there was a possibility that your
house’s metal work had become live.
It was called the WireAlert.