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on many projects, so we can’t start
on anything new, but we might consider updating these older projects at
some point.
We published a Universal Safety
Timer for Appliances (August 1990;
siliconchip.au/Article/6923), although
admittedly, that design could do with
an update. For example, it uses a Triac
as the switching device, so it would
not handle capacitive loads very well.
It also draws a little standby power.
We have also published numerous
soldering iron timer designs in Circuit
Notebook, including one in July 2020
(siliconchip.au/Article/14510) along
with March 2016, January 2007 and
October 1992.
Regarding the Soft Starter for Power
Tools with a switched slave output, we published two master/slave
mains power projects which could
have soft starting incorporated. They
are the PowerUp Master/Slave Power
Switch (July 2003; siliconchip.au/
Advertising Index
Altronics.................................27-30
Dave Thompson........................ 111
Digi-Key Electronics...................... 3
Emona Instruments.................. IBC
Jaycar.......................IFC, 10-11, 39,
...............................53, 60-61, 74-75
Keith Rippon Kit Assembly....... 111
LD Electronics........................... 111
LEDsales................................... 111
Microchip Technology.................. 5
Mouser Electronics..................OBC
Article/3905) and the Circuit Notebook
entry titled “Anto-sensing master/
slave power control“ (October 2010;
siliconchip.au/Article/321).
Given the age of these designs, it is
probably worthwhile for us to revisit
these ideas when we get a chance.
Wanted: comprehensive
portable audio test set
I have recently been helping my son
install subwoofers in his friends’ cars,
along with a couple of head units. They
pick up an amplifier, speakers and subwoofer pretty cheaply second-hand
from online marketplaces.
We’ve found that sometimes it
doesn’t work, so you need some way
of testing each segment, which has
proven cumbersome. Has there been a
project or two that would make a set of
test tools to work through the pieces?
Should we make one? For instance, the
following things need to be checked:
Head-unit: are the speaker outputs
working? Are the line-level outputs
working? Is the line-level output LF
only, or full-frequency? What voltage
level/volume is being produced?
Amplifier: what is the power supply voltage? Does it fluctuate under
load? Does the ignition key switch the
power, or is it a direct battery feed?
What is the output level and what is
the signal frequency range? It would be
helpful to be able to feed in a line-level
signal and provide a frequency sweep.
Control wire: did we find the right
one? When does it switch?
Speakers: an impedance tester
would be helpful, along with a way
to determine the phasing of dual-coil
drivers (they are relatively rare).
Ocean Controls............................. 9
SC USB Cable Tester................ 107
Silicon Chip PDFs on USB....... 109
Silicon Chip Shop.................88-89
Silicon Chip Subscriptions........ 47
Silicon Chip Test Tweezers..... 106
Silicon Chip 500W Amplifier..... 12
Silvertone...................................... 6
The Loudspeaker Kit.com............ 7
Tronixlabs.................................. 111
Wagner Electronics..................... 13
112
Silicon Chip
Errata and Next Issue
SC GPS Analog Clock................... 8
Cables: check for resistance and
continuity.
Some of these tests do fit under the
basic multimeter regime. Some might
be as simple as an audio cable from a
smartphone with the correct impedance/level. (L. C., Donvale, Vic)
● There is no easy way to make up a
universal test set for what you want.
However, you can use separate items
such as a multimeter, oscillator and
load resistances.
A multimeter can be sufficient for
most of the tests required, especially
if it is suitable for measuring AC voltages up to 1kHz or more.
A signal generator would be helpful
to provide a source for the amplifiers
under test. We’ve published a few useful portable oscillators:
• Shirt-pocket, Crystal-locked
Audio DDS Oscillator (September
2020; siliconchip.au/Article/14563)
• Roadies’ Test Oscillator (June
2020; siliconchip.au/Article/14466)
• Digital Audio Signal Generator
(March-May 2010; siliconchip.au/
Series/1)
Both the Shirt-pocket Oscillator and
Digital Audio Signal Generator would
be helpful for testing subwoofers as
they have adjustable frequencies.
Alternatively, a low-cost commercial
audio oscillator could be used.
A load for the amplifier can be made
using a heatsink and power resistors. element14 and RS Components
both sell high-power resistors. You
can connect them in series or parallel to achieve the required resistance
and power rating(s). element14 also
sells 100W-rated 4Ω & 8Ω chassis-
mount resistors (Cat Nos 2925455
and 2925462).
SC
WiFi DC Electronic Load, September & October 2022: (1) REG1 is shown
reversed on the main Load PCB silkscreening and in Fig.10. Fit it the other way
around, as shown in the photo on page 91 of the October 2022 issue.
(2) a design error on the main Load PCB means that the SDA line (pin 5 on
the CONTROL header, CON1) is likely to be shorted to GND due to a GND
via placed too close to that track. The via is just above and to the left of IC5
(labelled “DAC” on the PCB). Run a sharp knife between the GND fill and the
SDA track to clear the short, or drill out the top side of that via with a small
(eg, 2mm) drill bit.
(3) the sole 240W resistor on the main Load board should be 470W, to match
the source impedance of pin 1 of IC3 (1kW || 1kW). If built with the 240W
resistor, the resulting error will be minimal and likely cancelled out during
calibration.
(4) IC3 & IC4 were incorrectly listed as the INA180B4 type (gain = 200) in the
parts list. They must be the B1 type (gain = 20) for correct operation.
Next Issue: the January 2022 issue is due on sale in newsagents by Thursday,
December 29th. Expect postal delivery of subscription copies in Australia
between December 28th and January 13th.
Australia's electronics magazine
siliconchip.com.au
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