Ultrasonic Distance Meter

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  • Topic: Operational amplifier, Ultrasonic sensor, Rectifier
  • Pages : 20 (3271 words )
  • Download(s) : 289
  • Published : October 31, 2012
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ConstruCtion

microcontroller-based
Ultrasonic distance meter
and receiver), current buffer ULN2003,
operational amplifier LM324, inverter
here are several ways to measCD4049, four 7-segment displays, five ure distance without contact.
transistors and some discreet comOne way is to use ultrasonic ponents. The ultrasonic transmitterwaves at 40 kHz for distance measurereceiver pair is shown in Fig. 1. ment. Ultrasonic transducers measure

Ultrasonic generators use piezothe amount of time taken for a pulse of electric materials such as zinc or lead
sound to travel to a particular surface
zirconium tartrates or quartz crystal.
and return as the reflected echo.
The material thickness decides the
This circuit calculates the distance
resonant frequency when mounted
based on the speed of sound at 25°C
and excited by electrodes attached on
ambient temperature and shows it
either side of it. The medical scanners
o n a 7-segment display. Using it,
used for abdomen or heart ultrasound
you can measure distance up to 2.5
are designed at 2.5 MHz. In this cirmetres.
cuit, a 40kHz transducer is used for
For this particular application, the
measurement in the air medium. The
required components are AT89C2051
velocity of sound in the air is around
microcontroller, two 40kHz ultrasonic
330 m/s at 0°C and varies with temtransducers (one each for transmitter perature.
In this project, you excite the ultrasonic transmitter unit with a 40kHz pulse burst and expect an echo from
the object whose distance you want to
measure. Fig. 2 shows the transmitted
burst, which lasts for a period of approximately 0.5 ms. It travels to the object in the air and the echo signal
is picked up by another ultrasonic
Fig. 1: Ultrasonic transmitter and receiver pair
transducer unit (receiver), also a 40
kHz pre-tuned unit. The received signal, which is very
weak, is amplified several
times in the receiver circuit
and appears somewhat as
shown in Fig. 2 when seen
on a CRO.
Weak echoes also occur
d ue to the signals being
directly received through
the side lobes. These are
i gnored as the real echo
received alone would give
the correct distance. That
is why we should have a
l evel control. Of course,
the signal gets weaker if
the target is farther than
2.5 metres and will need a
Fig. 2: The ultrasonic pulse, echo signal and time measurement 

K. Padmanabhan

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higher pulse excitation voltage or a
better transducer.
Here the microcontroller is used to
generate 40kHz sound pulses. It reads
when the echo arrives; it finds the time
taken in microseconds for to-and-fro
travel of sound waves. Using velocity
of 333 m/s, it does the calculations and
ParTs LisT
Semiconductors:
IC1
- AT89C2051
microcontroller
IC2
- ULN2003 current buffer
IC3
- CD4049 hex inverting
buffer
IC4
- LM324 quad operational
amplifier
IC5
- 7815, 15V regulator
IC6
- 7915, -15V regulator
IC7
- 7805, 5V regulator
T1-T4
- BC557 pnp transistor
T5
- 2N2222 npn transistor
D1, D2
- 1N4148 switching diode
D3-D6
- 1N4007 rectifier diode
DIS1-DIS4
- LTS 542 common-anode,
7-segment display
Resistors (all ¼-watt, ±5% carbon):
R1, R2
- 2-mega-ohm
R3
- 82-kilo-ohm
R4, R7-R10
- 10-kilo-ohm
R5
- 33-kilo-ohm
R6
- 100-kilo-ohm
R11
- 1-kilo-ohm
R12-R15
- 1.2-kilo-ohm
R16
- 220-ohm
RNW1
- 10-kilo-ohm resistor
network
VR1
- 1-kilo-ohm preset
Capacitors:
C1, C2
- 3.3nF ceramic disk
C7, C10-C12
- 0.1µF ceramic disk
C3
- 2.2nF ceramic disk
C4
- 10µF, 16V electrolytic
C5, C6
- 22pF ceramic disk
C8, C9
- 1000µF, 50V electrolytic
Miscellaneous:
X1
- 230V AC primary to
15V-0-15V, 500mA
secondary transformer
XTAL
- 12MHz crystal
S1
- Push-to-on switch
S2
- On/off switch
TX1
- 40kHz ultrasonic
transmitter
RX1
- 40kHz ultrasonic receiver

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ConstruCtion
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