READER-TO-READER TECHFORUM
>>> QUESTIONS
Reactive Transformerless
Power Supply
How does one calculate the value
for the reactance capacitor in an AC to
DC reactive power supply so as not to
over-work the zener diode? I have
used from . 68 µf to 4. 7 µf for various
voltages out, but it has always been
trial and error.
#10101
Racing Game Data Logging
I want to connect an analog
tachometer and speedo or an
instrument cluster to a PC via USB for
receiving data from the Live For Speed
racing game.
What Arduino and circuit components do I need to use on this project
and which software is more useful?
#10105 Ozgur
Michael Stevens
Rogersville, AL
Ping Tester
I work in large building complexes
and need to "ping" devices several
floors away or in the next building. I
typically use a laptop, but it's difficult
to hold or set down while in riser or
mechanical rooms. There are cable
testers with ping functionality but they
are costly. It would be a neat project
to build a ping tester using one of the
widely available development boards
and microcontrollers. There are so
many choices I don't know where to
start. Could someone point me in the
right direction?
#10102 Jim, via email
Adapter Board
I recently got a Needham PB- 10
EPROM programmer. It can program
4751H microcontrollers, but requires
an adapter board to do so. I can't find
any info on this board. Does anyone
have a schematic or info so I could roll
my own?
#10103 Pierre Olivier, Quebec
[#4105 - April 2010]
Steampunk Keyboard
I am building a Steampunk
keyboard for my own use. I would like
to have a small motor spin some gears
each time a key is pressed on the
computer keyboard. I have not been
able to locate an encoder output or an
activity monitor that will show key
presses. I don't care which keys are
being pressed, and the gears spinning
are just for show. I would like a hardware solution over a software solution
— but a complete *.exe program would
be acceptable. (Maybe flashing the
scroll lock LED when keyboard activity
is being transmitted to the keyboard
controller.) Monitoring the data stream
for F0 (Key up)
occurrences would
also work.
>>> ANSWERS
teed to be pulled low at the beginning
of a transfer. A simple monostable
555 can detect that low pulse and
lengthen it to provide a control for
your motor.
With the indicated values, the 555
should run the motor for 0.1s - 1.2s
(depending on the setting of R2). I
have included two options for
connecting your motor. Option 1
should work for small motors that
draw less than 0.2A and operate at 5V.
If you have any other configuration, I
recommend Option 2. If you feel that
the time isn't long/short enough, just
change the values of R1, R2, and C1
as needed (Max time = (R1 + R2) x C1
x 1.1; Min time = R1 x C1 x 1.1).
Daniel De Jager
Edgewood, WA
[#6101 - June 2010]
Floppy Interface
I am looking to buy or get enough
tips to design and build a device to do
service adjustments on old style
floppy drives that are used in music
keyboards. To run analysis and adjustment software, I have to remove the
drive from the keyboard and connect it
to a computer. But, the new computers
don't have floppy connectors any
78 October 2010
Resistance Inverter/Converter
I installed a dash from a Buick into
a Winnebago. The gas gauge in the
new dash requires 242 ohms for a
full and 42 for an empty reading. The
Winnebago sending unit gives a 10
ohms full and 180 ohms empty resistance reading. I need help in designing
a circuit to do this conversion.
#10104 Kenneth Lysek
Henderson, CO
The circuit diagram in Figure 1
should do the trick;
just connect 'IN' to
the keyboard’s data
line. The PS/2 data
line is normally held
high, but is guaran-
Figure 1
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