Advertising Index
Altronics.................................69-76
Ampec Technologies.................. 13
ADI Maxim Integrated................. 11
Dave Thompson.......................... 95
Dick Smith Contest..................... 77
Digi-Key Electronics...................... 5
Emona Instruments.................. IBC
Hare & Forbes............................ 2-3
Jaycar.............................. IFC,45-52
Keith Rippon Kit Assembly......... 95
LD Electronics............................. 95
LEDsales..................................... 95
Microchip Technology......... 7, OBC
Mouser Electronics....................... 9
Ocean Controls........................... 10
Phipps Electronics...................... 85
PMD Way..................................... 95
SC Christmas Decorations......... 63
Silicon Chip Shop.................90-91
Silicon Chip Subscriptions........ 68
Solder Master............................. 15
Switchmode Power Supplies..... 12
The Loudspeaker Kit.com.......... 87
Tronixlabs.................................... 95
Vintage Radio Repairs................ 95
Wagner Electronics..................... 14
Next issue release
The December 2021 issue is due
on sale in newsagents by Thursday,
November 25th. Expect postal
delivery of subscription copies in
Australia between November 23rd
and December 13th.
96
Silicon Chip
Controlling motor
speed with an Arduino
I want to build your June 2011 Motor
Speed Controller (siliconchip.com.au/
Article/1035) using the Jaycar KC5502
kit. Can the external potentiometer be
replaced by connecting to an Arduino
for speed control?
I have been purchasing motor controller boards from the website: www.
dimensionengineering.com (Sabertooth 2x12 R/C boards).
This alternative would be of great
interest to my group of friends that
also build Star Wars robots. I am
scratch-building robots having left aircraft engineering after 36 years. One of
my builds was in DIYODE magazine
issue 3. (F. H., Engadine, NSW)
• You can use an Arduino to control
the June 2011 Motor Speed Controller
via a pulse width modulated (PWM)
output. The PWM signal is filtered
to give a varying voltage to feed the
Speed Controller.
Disconnect the trimpot or potentiometer connected to the +IN1 input
(pin 1) of IC1 and instead, connect
the PWM output of the Arduino via
a 10kW resistor. The supply ground
of the Arduino must connect to the
Motor Controller ground.
PWM frequency should be set for at
least 500Hz so that the 10kW resistor
and existing 1μF capacitor at the +IN1
input provide a smooth DC voltage.
The motor speed can then adjusted by
varying the duty cycle of the PWM signal from the Arduino. A 50% duty will
result in 2.5V DC at the Motor Controller input and will set the motor at
full speed. A 0% duty cycle will turn
the motor off.
If you want the motor to run at
maximum speed when the duty is set
at 100%, change the 10kW resistor to
22kW and connect another 22kW resistor from the +IN1 input to ground.
This will effectively halve the applied
voltage.
Details on using PWM with Arduino
is covered in the tutorial at siliconchip.
com.au/link/abb7
Transformer for 20W
Class-A Amplifier
Where can I obtain the 160VA 16-016V shielded toroidal power transformer for the 20W Class-A Amplifier
Module project (May-September 2007;
siliconchip.com.au/Series/58)?
Australia’s electronics magazine
In Leo’s April 2011 article titled
“Fixing transformer buzz in the Class
A amplifier”, he suggests using an
18-0-18V transformer when the mains
is reduced to 230V AC (it’s around
239V AC here in Melbourne suburbia)
and adding chokes which reduce the
DC output voltage of the power supply by more than a volt.
As ordinary 16-0-16V toroidal transformers are not off-the-shelf items (it’s
either 15-0-15V or 18-0-18V), should
I be looking to get an 18-0-18V transformer?
In the 1998 15W Class-A amplifier
version, its designers had lots of trouble with hum, even when using the
transformer inside a steel box inside
the amplifier chassis.
Would an ordinary unshielded
160VA toroidal transformer be OK if
placed about 400mm below the Class
A amplifier PCB, as in the separate
power supply version of 1998? (I. H.,
Essendon, Vic)
• We checked all four articles and
couldn’t find any mention of a source
for the transformer. These were supplied with the contemporary kits but
they have long since sold out. It was
probably made by either Harbuch or
Tortech. Regardless, either of them
should be able to wind one for you.
Email sales<at>harbuch.com.au or see
siliconchip.com.au/link/abba
Don’t forget to specify the electrostatic shielding.
You should be able to use the 18-018V transformer. If the voltage ends
up being too high, wind on extra turns
in the opposing direction to the original winding for each 18V winding to
reduce the voltage. But the chokes will
probably drop the voltages enough.
Placing the transformer in a separate box will reduce the hum significantly. 400mm spacing from the
amplifier should be sufficient. If hum
is still heard, try rotating the toroid to
get the lowest hum or move the toroid
further away.
Finally, note that the 20W Class-A
amplifier is essentially made obsolete
by the Ultra-LD Mk.3 (July-September
2011; siliconchip.com.au/Series/286)
and Mk.4 amplifiers (August-October
2015; siliconchip.com.au/Series/289),
which have similar distortion (lower
in the case of the Mk.4), significantly
more power and higher efficiency.
Importantly, they also do not suffer
from the same hum problems that
plague Class-A amplifiers.
SC
siliconchip.com.au
