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MARKET CENTRE
Cash in your surplus gear. Advertise it here in SILICON CHIP
KIT ASSEMBLY & REPAIR
KEITH RIPPON KIT ASSEMBLY &
REPAIR:
* Australia & New Zealand;
* Small production runs.
Phone Keith 0409 662 794.
keith.rippon<at>gmail.com
FOR SALE
LEDs! Nichia, Cree and other brand
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drivers, including ultra-reliable linear
driver options. Many other interesting
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PCBs & Micros: Silicon Chip Pub
lications can supply PCBs and programmed micros for all recent (and
some not so recent) projects described
in the magazine – see the PartShop advert in this issue. Order online or phone
(02) 9939 3295.
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230W Poly $190.
AGM Batteries: 7AH $19.50, 9AH
$24.50, 20AH $52.50, 55AH $129,
105AH $199, 220AH $399.
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544 High St, Preston 3072, Melbourne.
PCBs MADE, ONE OR MANY. Any
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Electronics Phone (02) 8068 2713.
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www.sesame.com.au
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WANTED
CIRCUIT & DESIGN IDEAS: SILICON
CHIP pays up to $60 for Circut Notebook items or you could win a $150 gift
voucher from Hare & Forbes. See the
Circuit Notebook pages for details.
ADVERTISING IN MARKET CENTRE
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WARNING!
SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such
projects should be considered dangerous or even lethal if not used safely.
Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When
working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages
or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages,
you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should
anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine.
Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability
for projects which are used in such a way as to infringe relevant government regulations and by-laws.
Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the
Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable.
siliconchip.com.au
June 2013 95
Advertising Index
Ask SILICON CHIP
. . . continued from page 94
has two read-out modes: percent gradient and degrees. In percent gradient
mode, it will read 0-100 when rotated
up to 45°, then just shows dashes
above 45°. It sounds like your chip is
in gradient mode.
To switch modes, hold down the
calibration button for at least five seconds after it is switched on. It should
then be in degrees mode and you can
re-calibrate as necessary.
Capacitor discharge
for points motors
The circuit diagram for the Capacitor Discharge Unit (SILICON CHIP,
March 2013) indicates that it is suitable for both AC and DC power supplies. The unit apparently half-wave
rectifies an AC supply, increasing the
RMS voltage to peak voltage, thereby
almost doubling its power potential.
By contrast, a DC current through
the unit with no increase in voltage
suffers voltage drops through the
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transistor and two diodes, making its
power potential less than that of the
AC power supply. It seems to me that
the unit is not intended to be used with
a DC power source. (J. M., via email).
• There is no problem with using AC
or DC. We referred your email to the
designer, Jeff Monegal, and his reply
is below.
It should be remembered that although there is a silicon diode and the
voltage drop across the transistor is in
series between the power supply and
the storage capacitors, there is very
little current flow. In fact, forgetting
leakage current through the capacitors,
the only current flow is that though
the LED – only around 9mA. This will
mean very little voltage drop across
the diode and transistor.
When either pushbutton is pressed,
Notes & Errata
Digital Sound Effects Generator,
September 2012: while the LM4889
was specified as an alternative to the
LM4819 audio amplifier IC, we have
discovered that the shutdown pin
polarity of the LM4889 is opposite to
that of the LM4819 (active low rather
than active high). We recommend
constructors stick with the LM4819.
1W LED Driver With Protection, Circuit Notebook, May 2013: the second and third paragraphs in the third
96 Silicon Chip
column should say “With an open
circuit, the voltage across the 220µF
capacitor can become as high as the
supply, damaging the LEDs should
they be reconnected with this higher
voltage present. With the protection
circuit, a higher than normal voltage
allows ZD1 to conduct, pulling pin
5 of IC2b higher than its inverting
input. This occurs with about 1mA
through ZD1 and 1V across each
1kΩ resistor. So there is about 10.2V
across the 220µF capacitor”.
Altronics....................... Loose Insert
Embedded Logic Solutions.......... 91
Emona Instruments........................ 5
Grantronics................................... 95
Harbuch Electronics..................... 85
Hare & Forbes.......................... OBC
HK Wentworth................................ 3
Instant PCBs................................ 95
Jaycar .............................. IFC,45-52
Keith Rippon ................................ 95
KitStop.......................................... 87
LED Sales.................................... 95
Low Energy Developments.......... 95
Microchip Technology................... 25
Mikroelektronika......................... IBC
Ocean Controls............................ 12
Premier Batteries........................... 7
Quest Electronics......................... 95
Radio, TV & Hobbies DVD............ 87
RF Modules.................................. 96
Sesame Electronics..................... 95
Silicon Chip Binders..................... 84
Silicon Chip Online Shop........ 88-89
Silicon Chip Subscriptions........... 35
Syndetic Pty Ltd............................. 9
Tekmark Australia......................... 55
Tenrod Pty Ltd.............................. 11
Wiltronics................................. 23,44
Worldwide Elect. Components..... 96
the coil of the point motor sees all
of the voltage across the capacitor(s)
minus the voltage drop across the
output diode.
To say it seems that the CDU is
meant for AC and not DC is incorrect
because the CDU will work fine with
DC. The Peco point motor we used operated well with a coil voltage of 12V
DC. While it is true that a higher voltage will be available with AC power in,
the point motor will operate fine with
a DC voltage of around 15V or more.
I set up a CDU and obtained the
following results:
• 15V DC gave 14.1V across the capacitors;
• 13V AC gave 15.4V across the capacitors; and
• 16.1V AC gave 18.9V across the
capacitors.
These figures were with no load
connected to the output. The only load
SC
was the LED (9mA).
siliconchip.com.au
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