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includes interfaces to USB ports.
How does an interpole winding
work in a DC motor?
[#12092 - December 2009]
I read the Oct ‘09 article on “The
Green Standby” and was wondering if
there is a circuit that would turn on or
off all the cube powered equipment
attached to my computer when it
first gets turned on.
Sears sells a device to do exactly
what you need for $19.99. It’s called
the Craftsman 24031 Auto Switch.
You can buy it at Sears.com, or see
for a review and more information.
That will be cheaper than the parts
needed to build one by hand.
It is made to automatically cut off
a dust collector when you turn off
your saw. It runs on 120 VAC, uses a
standard plug, and has one master and
two accessory outlets. Plug your
computer into the outlet labeled
"Power Tool" and an outlet strip with
the cube or other items into either of
the accessory outlets.
[#12093 - December 2009]
H-bridge/Relay for Trolling Motor
I'm designing a dual 12V, 50-
pound-thrust trolling motor assembly
for a small boat. It will run from 24V to
achieve brief bursts of relatively high
speeds on an engine-restricted local
lake. I’ll be using two independent
PICAXE controllers for direction and
speed control for each motor. Should I
use a semiconductor H-bridge or a
relay to switch directions on the
motors? I'm leaning heavily towards a
relay for simplicity. Also, I need a part
or circuit that can be driven with the
PICAXE-level PWM signal and control
the 12V motor (running from 24V)
with an unknown surge current level
(possibly over 100 amps per motor).
Since you are using PWM, the
easiest approach is to go with a full H-bridge and N-Channel MOSFETs
throughout. An excellent application
note for a low voltage H-bridge motor
drive is the Motorola Semi AN1319. It
was written to show the application of
their MDC1000A — a MOS turn-off
device. It was designed for 24-48 volt
applications. Although there are
now faster devices available from
Microchip and other vendors, it shows
a good implementation of a high-side
N-Channel MOSFET with a unique
charge pump. The switching signals
are transmitted through current
sources which are supply-voltage
independent and fast (no opto-coupler).
The high-side MOSFET is driven
through another current source which
allows fine-tuning the turn-on
characteristic. Turn-off is accomplished with the MDC1000A (which
can be replaced by two transistors,
two resistors, and two diodes).
[#12094 - December 2009]
Voice Phrase Toy
I want to embed four different
short voice phrases that I'll record
beforehand and load on to a device
that plays them from pushing one of
four buttons out of an eight ohm
speaker. Wondering if anyone has a
schematic or something on the code
to point me in the right direction.
#1 The ISD ChipCorder line of
devices should fit your needs nicely.
These devices come in a variety
of configurations, need few external
components, and generally have an
eight-ohm speaker amplifier built right
in. Most, though not all, of these
devices are in stock at Digi-Key.
You can see the product overview
at this address:
Cedar Rapids, IA
#2 One thought is to look at the
greeting cards that can record a
phrase and then play it back when
the receiver of the card opens it.
The card I had cost $7. Maybe
four cheaper ones? You can easily rip
the board out of the cards. Almost
everything you need is there —
batteries, microphone, and speaker.
Mine had three batteries hardwired in;
no idea how long they'd last though.
You can buy the raw recording/
playback systems. Amazon has them.
Do a search on "recordable greeting
card." They had a set of 40 of them for
$165 or a set of two for $26. Possibly
cheaper to find the cards on sale at
your local drug store.
#3 AllElectronics.com sells a
little movie promo toy called the Saw
3 Digital Voice Recorder for a mere
$2. It can be taken apart to do
exactly what you want. The (up to)
30 second recorded message is in
volatile memory, I think, so you may