This document introduces an ultrasonic range finder circuit project. It provides an overview of the circuit, including descriptions of its main components and their functions: transducers that transmit and receive ultrasound, oscillators that generate pulses, and circuits for signal amplification, time measurement, counting, display, and more. The circuit works by transmitting ultrasound pulses and measuring the time for echoes to return, then using that time to calculate distance. It outputs results on a 3-digit LED display in centimeters.

1. Welcome

2. Presentation of the final year Project
July 6, 2011
Mr. BERKOUK Hicham
Digital
Under the supervision of: Mr. HAMADACHE
Ultrasonic Range finder

3. Outline
Introduction
Project overview
Circuit operation
Circuit adjustments
Conclusion

4. Introduction
Ultrasound and piezoelectricity are two physical phenomena
strongly related to the operation of the ultrasonic range finder,
hence they should be defined.
 Ultrasound is cyclic sound pressure with a frequency greater
than the upper limit of human hearing.

5. Introduction
The applications of ultrasound are:
• Medical sonography
• Ultrasonic testing
• Ultrasonic cleaning
• Ultrasonic welding
• Sonochemistry
• Ultrasonic weaponry
• Ultrasonic range finding

6. Introduction
 Piezoelectricity is the charge which accumulates in certain
solid materials (notably crystals) in response to applied
mechanical stress. In other words, piezoelectricity is the
electricity resulting from pressure.
The applications of piezoelectricity are:
• Piezo-based ignition systems
• Piezoelectric transformers
• Piezoelectric sensors
• Piezoelectric actuators
• Quartz crystals
• SONAR

7. Introduction
 Ultrasonic range finding, called also SONAR (Sound Navigation
and Ranging), is a technique used to measure how far away
objects are from an ultrasonic source.
The principle of operation of ultrasonic range finding is:
An ultrasonic pulse is generated in a given direction. If there is
an object in the path of this pulse, part or all of this pulse will be
reflected back to the transmitter as an echo and can be detected
through the receiver path. By measuring the difference in time
between the pulse being transmitted and the echo being
received, it is possible to determine how far away the object is.

8. Introduction

9. Introduction
The applications of ultrasonic range finding are:
• Autofocus cameras.
• Motion detection.
• Robotics guidance.
• Proximity sensing.

10. Project overview
 Ultrasound physics:
In air, ultrasound travels by compression and rarefaction
(expansion) of air molecules in the direction of travel
(longitudinal motion).
As sound is a wave it is defined with parameters that
characterize waves, namely: speed of propagation (), frequency
() and wavelength ().

11. Project overview

12. Project overview
• The period () is the time needed for one wave cycle to
occur, measured in seconds.
• The wavelength is the distance travelled by a wave in one
period.
• The frequency () is the number of cycles that occur in one
second, measured in Hertz.
From the definitions of frequency and period, we can deduce the
frequency.
/

13. Project overview
To find the speed of ultrasound, we use the general definition of
speed which is the distance travelled over the time required for
that.
Speed= distance/time
Using this latter equation and the definition of the wavelength,
we can deduce the speed of ultrasound ():
/
/ Then, ×

14. Project overview
The speed of ultrasound in air varies essentially in function of air
temperature. In fact, it can be found using the following
equation:
V²=×R×
Where: : is the adiabatic index of air, =1,4.
R: is a constant, R=287 J/kg/°K.
T: is the temperature of air in kelvin (T=C°+273,15).

15. Project overview
The following table gives the speed of sound for different air
temperature values.
Temperature (°C) Speed of sound (m/s)
-20 319
-10 327
0 332
10 337
20 343
30 349

16. Project overview
The speed that will be used in this project is 343 m/s at 20 °C
because 20°C is near to the mean temperature value on earth.
Knowing that the frequency of the transducers used in this
project is 40kHz, we can compute the wavelength of our
waveform: =/ = 343/40k = 8,5 mm .

17. Project overview
 Ultrasonic range finder:
The circuit measures the time required for the pulse being sent
to come back as an echo to the receiver.

18. Project overview
As the pulse travels twice the same distance, so to find the time
we have to use a distance of 2×l.
∆t=2×l/
 General block diagram:
The following figure shows the general block diagram of the
ultrasonic range finder implemented in this project.

19. Project overview

20. Circuit operation
The ultrasonic range finder can be divided into the following
parts:
 Two ultrasonic transducers (emitter + receiver).
 Transmitter circuit.
 Receiver circuit
 Time duration detection and calculation circuit.
 Counter circuit.
 Decoder and display circuit.
In this chapter, the operation of each part is described.

21. Circuit operation
 Ultrasonic transducers:
They are used to send and detect the ultrasonic pulses.

22. Circuit operation
 Transmitter circuit:
The transmitter circuit is composed of two oscillators and a
monostable latch.
• Oscillators:

23. Circuit operation
This type of oscillators is called “CMOS relaxation oscillator”. Its
output is a square wave that has a frequency that can be
calculated using the following expression:
/2,2×R2×C1
(for 2nd oscillator, add value of A1)

24. Circuit operation
• Monostable latch:
A monostable latch is circuit that has two output states; one is
stable the other is unstable. The output of the latch stays stable,
indefinitely, unless a pulse is presented at its input and forces
the output to the unstable state. The time duration of the
unstable state is related to values of R and C. After that, the
output comes back to the stable state.
1
2
3
U2:A
4011
C 5
6
4
U2:B
4011
R
+Vdd

25. Circuit operation
This monostable latch has a low stable output. When a high is
presented at its input, the output goes high for time duration (t)
that can be found using the following expression:
t=R×C×ln2
 Receiver circuit:
The receiver circuit is composed of two parts: a differential
amplifier and a comparator.
• Differential amplifier:
Once the ultrasonic receiver detects the echo, it converts it to
voltage oscillations of some millivolts. These oscillations are
presented to the inverting input of a differential amplifier through
a coupling capacitor.

26. Circuit operation
The output of the differential amplifier can be found using the
following expression:
Vₒ= (1+ A/R’) × V₂ - (A/R’) × V₁
R'
R
R
A
+Vdd
C
Receiver
3
2
1
84
U1:A
LM358

27. Circuit operation
Where:
V₁: is the voltage from the receiver.
V₂: is the voltage on the non-inverting input, V₂= 4,5 V.
• Comparator:
It compares the output of the amplifier to a voltage reference on its
inverting input.
R2
R1
A
1
2
3
U1:A
4011
+Vdd
3
2
1
84
U2:B
LM358

28. Circuit operation
When the output of the amplifier is less than the voltage reference of
the comparator, this latter one will have a low output that will be
converted to a high by the inverter.
 Time duration detection and calculation circuit:
This circuit is composed of three parts: an RS flip-flop, an oscillator
and a Schmitt trigger.
• RS flip-flop:
1
2
3
U1:A
4001
5
6
4
U1:B
4001
S
R
Q

29. Circuit operation
The truth table for this flip-flop is given the following table.
Only the set and reset conditions will be used in this project.
S R Qn+1
0 0 Qn
0 1 0 (reset)
1 0 1 (set)
1 1 ?

30. Circuit operation
• Schmitt trigger:
It is used for noise immunity and to stop the range finder
operation when the maximum measurable value is overtook.
R2 8
9
10
U5:C
4011
12
13
11
U5:D
4011
R1
R3
C1

31. Circuit operation
 Counter circuit:
The counters used in this project are: CD 4029, which are
presettable up/down counters that count in either binary or
decade mode depending on the voltage level applied at
binary/decade input. When binary/decade is at logical “1”, the
counters count in binary, otherwise they count in decade.
Similarly, the counters count up when the up/down input is at
logical “1” and vice versa.
In this project, the counters count up and in decade mode
(binary-coded-decimal, BCD mode).

32. Circuit operation
 Decoder and display circuit:
• Decoders:
The decoders used in this project are: CD 4543, which are BCD-
to-seven segment latch/decoder/driver designed primarily for
liquid-crystal display (LCD) applications. They are also capable of
driving light emitting diode (LED), incandescent, gas-discharge,
and fluorescent displays.
In this project, the decoders are used for LED application
(common-anode ones), so we have to apply a logic “1” at the
phase inputs of these decoders.
• 7-segment display:
The 3-digit 7-segment display used in project is common-mode
type from ROHM Semiconductor.

33. Circuit operation
 General circuit operation:
The following figure shows the general schematic diagram of the
ultrasonic range finder.

34. 1
2
3
U1:A
4001R1
1M
5
6
4
U1:B
4001 C1
1u
R2
220k
C2
10n
R3
10k D1
1N4148
1
2
3
U2:A
4011
C3
22n
5
6
4
U2:B
4011
8
9
10
U2:C
4011
R4
22k
12
13
11
U2:D
4011
1
2
3
U3:A
4011
R6
22k C4
220pR5
220k
Transmitter
R7
220R
C5
1n
Receiver
R8
10k
R9
10k
R10
10k
R11
10k
+9 V
5
6
4
U3:B
4011
8
9
10
U3:C
4011
12
13
11
U3:D
4011
1
2
3
U5:A
4011
5
6
4
U5:B
4011R12
7k5
C6
2n2R13
100k
R14
10k
8
9
10
U5:C
4011
12
13
11
U5:D
4011
R15
22k
R16
10k C7
1n
A
5
B
3
C
2
D
4
CLK
6
LE
1
BI
7
QA
9
QB
10
QC
11
QD
12
QE
13
QF
15
QG
14
U6
4543
A
5
B
3
C
2
D
4
CLK
6
LE
1
BI
7
QA
9
QB
10
QC
11
QD
12
QE
13
QF
15
QG
14
U7
4543
A
5
B
3
C
2
D
4
CLK
6
LE
1
BI
7
QA
9
QB
10
QC
11
QD
12
QE
13
QF
15
QG
14
U8
4543
R17
220R
R18
220R
R19
220R
A
4
QA
6
B
12
QB
11
C
13
QC
14
D
3
QD
2
CI
5
CO
7
CLK
15
PE
1
B/D
9
U/D
10
U9
4029
A
4
QA
6
B
12
QB
11
C
13
QC
14
D
3
QD
2
CI
5
CO
7
CLK
15
PE
1
B/D
9
U/D
10
U10
4029
A
4
QA
6
B
12
QB
11
C
13
QC
14
D
3
QD
2
CI
5
CO
7
CLK
15
PE
1
B/D
9
U/D
10
U11
4029
D2
1N4148
D3
1N4148
D4
1N4148
C8
1n
A4
1M
A1
22k
A3
10k
+9 V +9 V +9 V
BAT1
9 V
C9
470n
SW1
SW-SPST
+9 V
+9 V +9 V +9 V
A2
10k
3
2
1
84
U4:A
LM358
3
2
1
84
U4:B
LM358

35. Circuit operation
The ultrasonic range finder circuit works as follows:
• The oscillator.1 oscillates at a frequency of 2 Hz. Its output is
connected to a monostable latch through a capacitor and to the
preset enable inputs of the counters. The capacitor discharges
quickly through a resistor, and hence gives a short pulse to the
preset enable inputs of the counters to clear them before they
start counting.
• The monostable latch is at a low stable output state. When it
receives a high input from the oscillator output, its output goes
high for time duration of 300 μs, hence it limits the transmission
time. The output is connected to the input of the oscillator.3 and
to the S input of the RS flip-flop.

36. Circuit operation
• The oscillator.3 is controlled by the output of the monostable latch.
When the output of the latch is high, the oscillator oscillates. So, in
this case, the oscillator oscillates for 300 μs at a frequency of 40
kHz, i.e. a period of 25 μs. The number of pulses to be sent is
300/25, which equals to 12 pulses. This oscillator drives the
ultrasonic transmitter, connected across an inverter to increase the
power of transmission.
• The ultrasonic receiver is connected to the inverting input of a
differential amplifier through a coupling capacitor. The non-
inverting input is connected to a voltage divider of +4,5 V. The
output of this amplifier is connected to the non-inverting input of a
comparator. The inverting input of the comparator is connected to
a voltage reference of value less than +4,5V by some millivolts.

37. Circuit operation
When an echo is present at the non-inverting input of the differential
amplifier, its output oscillates around the value of +4,5V and at some
time is less than the reference voltage at the inverting input of the
comparator. In this condition, the output of the comparator goes low.
This low state is converted to a high state by an inverter and
presented to the R input of the RS flip-flop.
• When the transmission operation starts, the output of the RS flip-
flop goes high and when an echo is received it goes low. The time
duration for the high state corresponds to the time needed for the
ultrasonic range finding operation. When the output of the flip-flop
goes high, the oscillator.3 becomes operational and delivers a
square wave output with a frequency that depends on the value of
the variable resistor in this oscillator.

38. Circuit operation
The output of this oscillator is connected to the clock input of the first
counter through a Schmitt trigger circuit. As we know, the counter
outputs are incremented by 1 each clock pulse and knowing that the
circuit displays the results in centimetres; so, the number of pulses
delivered by the oscillator should correspond to a value in
centimetres. We will see in the next chapter how to adjust the
variable resistor in order to have a frequency that gives the right
number of pulses.
When the first clock pulse raising edge is presented on the clock input
of the first counter (the counter of units), it starts counting. When
this counter reaches the value 9 (1001 in binary), the carry out output
(CO) will have a low value. This CO output is connected to the clock
input of the second counter. After that the first counter comes back to
the value 0000B and its CO output goes to the high value.

39. Circuit operation
This condition will increment the second counter. The same thing
happens for the second counter. When it reaches the value 9, its CO
output connected to the clock input of the third counter, goes low.
When the second counter comes back to zero, its CO output goes
high. In this situation, the third counter will be incremented.
If all the CO outputs are low, the circuit will stop counting and will
display the value 999. This situation occurs only when the distance is
greater than the maximum measurable range.
• As the results of the counters are in BCD, they will be decoded by
BCD to 7-segement display decoders before being displayed.

40. Circuit adjustments
An oscilloscope is needed in this practical part.
• Oscillator.2 40 kHz (=25μs).
Vary (A1) until we get on the oscilloscope a waveform having this
frequency.
• Oscillator.3
As we said in the previous chapter, the number of pulses delivered
by this oscillator corresponds to centimetres on the display.
∆t= 2×l/
= ∆t/n
Where; n: is number of cycles.
The number of cycles in this case is n= 100×l.

41. Circuit adjustments
The period then is: = ∆t/(100×l)
= (2×l/)/(100×l)
= 0,02/
=0,02/343 ≈ 60 μs.
Adjust the variable resistor (A3) until we get a waveform having a
period of 60 μs.
• Voltage gain:
What we need here, is to have the oscillating output of the amplifier
less than the reference voltage of the comparator at some time.
• Voltage reference of comparator:
We change the value of (A2) until we get a reference voltage value
less but close to the output voltage of amplifier at rest.

42. Conclusion
• In this work, an ultrasonic range finder has been realized to
perform different possible applications.
• The project allowed us to study a great number of other circuits;
such as, oscillators, monostable latches, and to use them to
perform a given application.
• The speed of ultrasound in air is affected by air temperature
variations. So, we can propose, for future improvements on the
circuit, to add a temperature sensor, with its circuitry, to take into
account these variations.
• We can also implement the range finder using a PIC
microcontroller and develop the corresponding software to perform
the required calculations.
The following figure shows an example of an improved ultrasonic
range finder.

43. Conclusion

44. Thank you for
your
attention