How it Works
As it has already been stated the circuit consists of an ultrasonic transmitter and a receiver both of which work at the same frequency. They use ultrasonic piezoelectric transducers as output and input devices respectively and their frequency of operation is determined by the particular devices in use.
The transmitter is built around two NAND gates of the four found in IC3 which are used here wired as inverters and in the particular circuit they form a multivibrator the output of which drives the transducer. The trimmer P2 adjusts the output frequency of the transmitter and for greater efficiency it should be made the same as the frequency of resonance of the transducers in use. The receiver similarly uses a transducer to receive the signals that are reflected back to it the output of which is amplified by the transistor TR3, and IC1 which is a 741 op-amp. The output of IC1 is taken to the non inverting input of IC2 the amplification factor of which is adjusted by means of P1. The circuit is adjusted in such a way as to stay in balance as long the same as the output frequency of the transmitter. If there is some movement in the area covered by the ultrasonic emission the signal
that is reflected back to the receiver becomes distorted and the circuit is thrown out of balance. The output of IC2 changes abruptly and the Schmitt trigger circuit which is built around the remaining two gates in IC3 is triggered. This drives the output transistors TR1,2 which in turn give a signal to the alarm system or if there is a relay connected to the circuit, in series with the collector of TR1, it becomes activated. The circuit works from 9-12 VDC and can be used with batteries or a power supply.
@Clean
the
component
leads
with
a
small
piece
of
emery
paper.
@Bend
them
at
the
correct
distance
from
the
component�s
body
and
insert
the
component
in
its
place
on
the
board.
@You
may
find
sometimes
a
component
with
heavier
gauge
leads
than
usual,
that
are
too
thick
to
enter
in
the
holes
of
the
p.c.
board.
@In
this
case
use
a
mini
drill
to
enlarge
the
holes
slightly.
Do
not
make
the
holes
too
large
as
this
is
going
to
make
soldering
difficult
afterwards.
@Take
the
hot
iron
and
place
its
tip
on
the
component
lead
while
holding
the
end
of
the
solder
wire
at
the
point
where
the
lead
emerges
from
the
board.
The
iron
tip
must
touch
the
lead
slightly
above
the
p.c.
board.
@When
the
solder
starts
to
melt
and
flow
wait
till
it
covers
evenly
the
area
around
the
hole
and
the
flux
boils
and
gets
out
from
underneath
the
solder.
The
whole
operation
should
not
take
more
than
5
seconds.
Remove
the
iron
and
allow
the
solder
to
cool
naturally
without
blowing
on
it
or
moving
the
component.
If
everything
was
done
properly
the
surface
of
the
joint
must
have
a
bright
metallic
finish
and
its
edges
should
be
smoothly
ended
on
the
component
lead
and
the
board
track.
If
the
solder
looks
dull,
cracked,
or
has
the
shape
of a
blob
then
you
have
made
a
dry
joint
and
you
should
remove
the
solder
(with
a
pump,
or a
solder
wick)
and
redo
it.
@Take
care
not
to
overheat
the
tracks
as
it
is
very
easy
to
lift
them
from
the
board
and
break
them.
@When
you
are
soldering
a
sensitive
component
it
is
good
practice
to
hold
the
lead
from
the
component
side
of
the
board
with
a
pair
of
long-nose
pliers
to
divert
any
heat
that
could
possibly
damage
the
component.
@Make
sure
that
you
do
not
use
more
solder
than
it
is
necessary
as
you
are
running
the
risk
of
short-circuiting
adjacent
tracks
on
the
board,
especially
if
they
are
very
close
together.
@When
you
finish
your
work
cut
off
the
excess
of
the
component
leads
and
clean
the
board
thoroughly
with
a
suitable
solvent
to
remove
all
flux
residues
that
may
still
remain
on
it.
@There
are
quite
a
few
components
in
the
circuit
and
you
should
be
careful
to
avoid
mistakes
that
will
be
difficult
to
trace
and
repair
afterwards.
Solder
first
the
pins
and
the
IC
sockets
and
then
following
if
that
is
possible
the
parts
list
the
resistors
the
trimmers
and
the
capacitors
paying
particular
attention
to
the
correct
orientation
of
the
electrolytic.
@Solder
then
the
transistors
and
the
diodes
taking
care
not
to
overheat
them
during
soldering.
The
transducers
should
be
positioned
in
such
a
way
as
they
do
not
affect
each
other
directly
because
this
will
reduce
the
efficiency
of
the
circuit.
When
you
finish
soldering,
check
your
work
to
make
sure
that
you
have
done
everything
properly,
and
then
insert
the
IC�s
in
their
sockets
paying
attention
to
their
correct
orientation
and
handling
IC3
with
great
care
as
it
is
of
the
CMOS
type
and
can
be
damaged
quite
easily
by
static
discharges.
Do
not
take
it
out
of
its
aluminum
foil
wrapper
till
it
is
time
to
insert
it
in
its
socket,
ground
the
board
and
your
body
to
discharge
static
electricity
and
then
insert
the
IC
carefully
in
its
socket.
In
the
kit
you
will
find
a
LED
and
a
resistor
of
560
�
which
will
help
you
to
make
the
necessary
adjustments
to
the
circuit.
Connect
the
resistor
in
series
with
the
LED
and
then
connect
them
between
point
9 of
the
circuit
and
the
positive
supply
rail
(point
1).
Connect
the
power
supply
across
points
1
(+)
and
2
(-)
of
the
p.c.
board
and
put
P1
at
roughly
its
middle
position.
Turn
then
P2
slowly
till
the
LED
lights
when
you
move
your
fingers
slightly
in
front
of
the
transducers.
If
you
have
a
frequency
counter
then
you
can
make
a
much
more
accurate
adjustment
of
the
circuit.
Connect
the
frequency
counter
across
the
transducer
and
adjust
P2
till
the
frequency
of
the
oscillator
is
exactly
the
same
as
the
resonant
frequency
of
the
transducer.
Adjust
then
P1
for
maximum
sensitivity.
Connecting
together
pins
7 &
8 on
the
p.c.
board
will
make
the
circuit
to
stay
triggered
till
it
is
manually
reset
after
an
alarm.
This
can
be
very
useful
if
you
want
to
know
that
there
was
an
attempt
to
enter
in
the
place
which
are
protected
by
the
radar.
Adjustments
This
kit
does
not
need
any
adjustments,
if
you
follow
the
building
instructions.
Warning
If
they
are
used
as
part
of a
larger
assembly
and
any
damage
is
caused,
our
company
bears
no
responsibility.
While
using
electrical
parts,
handle
power
supply
and
equipment
with
great
care,
following
safety
standards
as
described
by
international
specs
and
regulations.
If
it
does
not
work
Check
your
work
for
possible
dry
joints,
bridges
across
adjacent
tracks
or
soldering
flux
residues
that
usually
cause
problems.
Check
again
all
the
external
connections
to
and
from
the
circuit
to
see
if
there
is a
mistake
there.
See
that
there
are
no
components
missing
or
inserted
in
the
wrong
places.
Make
sure
that
all
the
polarised
components
have
been
soldered
the
right
way
round.
Make
sure
that
the
supply
has
the
correct
voltage
and
is
connected
the
right
way
round
to
your
circuit.
Check
your
project
for
faulty
or
damaged
components.
If
everything
checks
and
your
project
still
fails
to
work,
please
contact
your
retailer
and
the
Smart
Kit
Service
will
repair
it
for
you.
