ULTRASONIC MOTION DETECTOR
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Joined: Dec 2009
23-12-2009, 08:00 PM
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Joined: Dec 2009
24-12-2009, 07:17 PM
Ultrasonic motion detectors emit and receive ultrasonic sound energy in a region of interest.Object motion within the region of interest and in the range of the ultrasonic motion sensor is detected and an alarm signal is produced.The range of these detectors differs from the designed range whenever the actual atmospheric sound propogation conditions vary from the atmospheric conditions assumed in the design .Ultrasonic motion detectors are commonly used for automatic door openers and security alarms. ultrasonic beams are easily blocked by thin materials, including paper and as a result False triggering is easly caused by reflections from blowing curtains, pets, and flying insects.
The circuit uses a matched pair of 40 kHz transducer elements to detect movement up to 22 feet away. Crystal locked circuit for maximum stability. An LED is switched on for movement indication. The transmitter sends out a steady ultrasonic signal at 40kHz( wavelength ~= 6 mm).
The reflected sound is detected by ultrasonic receiver. The
signal is then amplified by amplifiers.An amplifier is selfbiasing. The time constant of the first amplifier is set to let the 40kHz signal through. Between
the first & second amplifier there is a negative peak
detector consisting two diodes which follows the envelope of
the 40kHz signal. If there is no movement the envelope is
just a straight line. The time constant ofsecond amplifier is much slower so that it will follow this envelope. When
there is no movement neither diodes can conduct. If the signal falls or rises the diodes conducts which the output to go high. A low pass filter screens out unwanted spurious signals. Specific details about the circuit are available in this link:
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Joined: Apr 2012
28-08-2012, 01:00 PM
Ultrasonic Motion Detector
ultrasonicdetector.pdf (Size: 168 KB / Downloads: 105)
Something's out there—on the porch,
in the driveway, or behind the shed. Or
maybe it's inside—in the garage,
basement, or den. Whatever it is, human or
beast, it is moving. Perhaps it's just your
teenager sneaking in from a late night out.
Possibly it is only the neighborhood cat.
Or, more ominously, it could be a prowler
bent on theft or physical harm. Whatever
is going on, you know something is up
because you just installed the Ultrasonic
Motion Detector described in this article.
Depending on what parts you have
available, or if you buy the complete kit
from the source mentioned in the Parts
List, the Ultrasonic Motion Detector can be
built for less than $30. It contains a
complete ultrasonic (40-kHz) crystalcontrolled
transmitter and a supersensitive
receiver on a printed-circuit board .
The schematic for the Ultrasonic
Motion Detector is shown in Fig. 1. A 9-volt
battery, B1, directly provides power for
some sections of the circuit. The battery is
also connected to a 78L05 regulator, IC3.
which provides a 5-volt-DC power source
for other sections of the circuit.
The transmitter section of the Detector
is basically a crystal-controlled relaxation
oscillator built around a 4049 hex inverter,
IC2. One of the 4049 sections, IC2-c, along
with resistors R21 and R22, and capacitors
C11 and C12, "pings" the 40-kHz crystal
into sustained oscillation. The remaining
4049 sections act as linear buffers to drive a
40-kHz ultrasonic transmitting transducer,
The author built the Ultrasonic Motion
Detector from a complete kit of parts,
which includes a pre-etched and drilled
PC board. That kit is available from the
source mentioned in the Parts List. If you
choose to round up your own
components, it is still recommended that
you use a PC board. You can use the foil
pattern shown in Fig. 2 to make your own.
Refer to the parts-placement diagram
shown in Fig. 3 while assembling your
circuit. Begin by soldering all resistors
flush to the PC board. Then install the five
diodes, making sure to orient them
properly. Next, install the capacitors. Be
sure to double check the polarity of C9.
Go on to install crystal XTAL1. Bend
the crystal's leads so that the part rests flat
on the board. Note the two unused holes
next to the two for the crystal. You can
bend a resistor lead around the crystal in a
"U" shape and solder the lead ends to the
unused holes. That should hold the crystal
Referring back to Fig. 1, note that
transistor Q1 turns on and delivers a
continuous unregulated 9 volts to a
suitable load as long as something is
moving within the Detector's range. If the
load is a 9-volt relay, virtually any
electronic device can be turned on in
response to motion. That might be good
enough for many applications˜lights can
be made to flash, horns to blare, etc. (If you
have trouble driving the coil of a 9-volt
relay, you might need to reduce the value
of R19 in Ql's base circuit.)
However, there are times when you
will want an output device to remain
activated after motion has stopped. For
example, if a prowler quickly crosses the
field of "view," you wouldn't want a
speaker to sound or a light to flash for just
an instant. Continuous signaling, perhaps
for many minutes, would be desirable.
The alarm circuit shown in Fig. 4 will
provide such a warning. It consists of three
555 timer ICs, IC1-IC3, where IC1 is
operated in a monostable mode, and IC2
and IC3 are in astable configurations.