a frequency-to-voltage converter. The
circuit in Figure 2 does just that.
It uses a 555 monostable timer to
output a defined-width pulse every
time the trigger input (pin 2) is activated.
The output pulse train is then
averaged to produce a “steady” DC
output. Using the CAL pot, the width
of the pulse is adjusted so that a 5,000
RPM input produces a 5 volt output.
Be warned, though, that most
cheap DMMs won’t respond to instantaneous changes in engine speed.
That’s because they have a low
sampling rate, so the reading will lag
behind the actual RPM by a second or
two while the DMM display stabilizes.
An analog meter (one with a pointer)
will respond faster. A 5K resistor in
series with a 0-1 mA panel meter will
show 5,000 RPM at full scale.
protocol and herein lies the problem.
The easiest conversion is between
a USB “A” female to PS/2 male adapter,
which lets you plug a USB mouse into
an PS/2 mouse port. However, this will
not work with every USB mouse! Your
USB mouse must be made so that it
can use one of these adapters.
Going from a PS/2 mouse to a
USB port takes a lot more work. That’s
because the PS/2 protocol uses interrupts for its serial communications
and the USB doesn’t. This requires
both hardware and software. A favorite
device among hobbyists is the
dual-port adapter that lets you plug
both your PS/2 mouse and keyboard
into one USB port. USB adapters run
between $12.00 and $75.00 — depending on features and compatibility —
and are available from RadioShack
(26-226) and most computer stores.
Other conversion protocols (parallel to
USB, etc.) are also available.
For those readers who wish to
make it yourself, Microchip serves up
a “PS/2 to USB Mouse Translator”
application note (TB055) that uses a
16C745 microcontroller (ww1.micro
s/91055C.pdf). A download of the
software is available from Microchip;
you have to program the chip yourself.
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PS/2 to USB
Q. Is there any way — perhaps with
hardware — to turn a regular
serial mouse into a USB mouse? I am
interested in the data communication
Phaser Pain Field Pistol
Experimental device for
animal control. Variable
and complex output over
130db. Do not point at
people! Higher powered
and rental units available.
PPP1K Kit ......................... $59.95
PPP10 Assembled............. $84.95
A. It depends on what you consider
to be a “regular” serial mouse.
Mice come in a number of shapes,
sizes, and interfaces. Just a few years
ago, serial mice (with DB- 9 connectors) were quite popular, but the computer industry has all but abandoned
them in support of USB and PS/2
devices. Each interface uses a different
IDE to SCSI?
Q. This question is about SCSI and
IDE hard drives. I recently
acquired a new SCSI hard drive and
would like to install it into my PC,
which has a built-in IDE controller. Is
Gas Engine Tach
5V = 5,000 RPM
Burning Laser Ray Gun
Uses our sealed
CO laser tube and
current source to
generate a continous beam capable of
lighting fires over distances. Operates
12 vdc with optional inverter for field or
115vac for lab use.
LABURN1 Plans ................. $20.00
(all parts available)
Box 716, Amherst, NH 03031 USA
Circle #122 on the Reader Service Card. 33