Underwater communication system by means of coded pulses

An underwater communication system by coded pulses, includes a transmitter placed at a surface of a body of water, for transmitting coded pulses, the transmitter having a transmitter circuit for generating the coded pulses, the transmitter circuit including a first shift register pre-programmed with a binary code corresponding to the coded pulses, and an underwater piezoelectric transducer for submersion in the water and electrically connected with the transmitter circuit for transmitting the coded pulses through the water; an underwater receiver for receiving the transmitted coded pulses, without any physical connection between the transmitter and receiver, the receiver having an underwater piezoelectric transducer, submerged in the water, for receiving the transmitted coded pulses, and a receiver circuit for comparing the received code pulses with stored coded pulses, the receiver circuit including an amplifier for amplifying the received coded pulses, an internal clock generator for generating a clock signal, a circuit for synchronizing the received and amplified coded pulses with the generated clock signal, a second shift register pre-programmed with the binary code corresponding to the coded pulses, and a comparator for comparing the received coded pulses with the code pre-programmed into the second memory, to verify that the received coded pulses correspond to the code pre-programmed into the second memory; and an actuator for releasing a submerged object in response to verification by the comparator that the received coded pulses correspond to the code pre-programmed into the second memory.

BACKGROUND OF THE INVENTION 
The present invention relates to an underwater communication system 
utilizing coded pulses transmitted by an on-surface transmitter connected 
to a first underwater piezoelectric transducer and which are received by a 
submerged receiver connected to a second underwater piezoelectric 
transducer, without any physical connection between the transmitter and 
the receiver. 
There are presently two known ways to transmit a signal through a liquid 
medium between an object on the surface and an underwater object, namely 
(i) cable communication and (ii) transmitting sonic or ultrasonic waves 
that are reflected back to the emitting source. 
In the first case, the sending device necessarily has to be wired to the 
receiving device in order for both devices to be able to transmit and to 
receive. However, the length of the connecting cable and the problems of 
setting the cable, limit the use of this method to short distance 
communication, since the devices are connected together. 
In the second case, there is no connection such as a wire between the 
transmitter and the receiver. Rather, a pulse is transmitted through the 
liquid, reflected without any change by the receiver and received by the 
transmitter itself. This is the principle on which echo sounders are 
based, and can only work if there are no reflecting objects between the 
transmitter and the receiver. Moreover, it is not possible to establish a 
two way connection, since the submerged body behaves only as a reflector 
and cannot send self-created signals. Thus, an echo sounder only measures 
the distance of the reflecting object. 
OBJECTS AND SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide an 
underwater communication system that overcomes the problems with the 
aforementioned prior art. 
It is another object of the present invention to provide an underwater 
communication system that allows a two way wireless communication by means 
of coded pulses between two devices, with one device being on the surface 
and the other submerged, or both being submerged in a liquid, such as a 
sea, lake, river, etc. 
It is still another object of the present invention to provide an 
underwater communication system in which a uni-directional communication 
can be made bi-directional by modifying the circuits of the two 
transmitting-receiving devices. 
The above objects are achieved by an underwater communication system in 
which a transmittent source of pulses is placed at the surface of the 
water and is connected to an underwater piezoelectric transducer submerged 
just below the surface of the water. A receiver is positioned in the 
water, for example, on the seabed, and receives the pulses transmitted by 
the transmitter, through another underwater piezoelectric transducer to 
which the receiver is connected. 
The underwater communication system can be made uni-directional or 
hi-directional, that is, the communication between the two devices may be 
one of only transmitting, only receiving or both transmitting and 
receiving. Such communication is carried out with the transmission from 
the transmitter to the receiver of sonic or ultrasonic pulses, at the 
characteristic frequency of the transducer that is used. 
The transmitter generates a signal with a suitable frequency and pulse 
width, for example, a frequency pulse of 200 KHz during an on or 
transmission period of 200 microseconds (.mu.sec), and with an interval 
between consecutive pulses of 20 milliseconds (msec). However, the values 
of the frequency (KHz), pulse duration (.mu.sec) and interval (msec) can 
be any suitable values, with their values varying in dependence on the 
specific application. For example, there can be a frequency pulse of 200 
KHz during an on or transmission period of 320 microseconds (.mu.sec), 
with an interval between consecutive pulses of 20.48 milliseconds (msec). 
In such case, the total period is 20.8 msec, that is, 20.48 msec plus 320 
.mu.sec. As another example, there can be a frequency pulse of 120 KHz 
during an on or transmission period of 70 microseconds (.mu.sec), with an 
interval between consecutive pulses of 7.5 milliseconds (msec). 
The pulses generated by the transmitter are sent through a shift register 
which is pre-programmed with the selected key or code, to the underwater 
piezoelectric transducer. Preferably, the preset code is a binary type 
code, where "1" represents a pulse and "0" represents the absence of a 
pulse, with the code including any number of bits. Thus, the transmitter 
sends coded pulses. 
The receiver includes an underwater transducer similar to the transducer in 
the transmitter. The pulses sent by the transmitter are received and 
amplified in the receiver. The receiver includes an oscillator which 
generates a time interval clock signal with the same period as the 
transmitted signal, for example, 20 msec. Upon reception of the first 
pulse, the receiver synchronizes its clock with that of the received 
signal. The subsequent pulses, which include data, are regenerated and 
widened for better reliability, and supplied to the DATA input of a serial 
in, parallel out (SIPO) shift register which has been pre-programmed with 
the same key or code of the transmitter. The generated clock is also 
supplied to the CLOCK input of the shift register. At this time, an "open 
gate" condition exists. 
When the preset code is received at the shift register, a pulse is 
generated, which can be used for any of different purposes. For example, 
in a preferred embodiment, this pulse controls an actuator of a mechanical 
device, and is also used for synchronization for the reception of 
subsequent information that can be characters, numbers, controls, etc. In 
this manner, an exchange of information has been achieved between the 
transmitter and receiver, using the water as a means of conduction of this 
exchange. 
In accordance with an aspect of the present invention, an underwater 
communication system by means of coded pulses, includes transmitter means, 
placed at a surface of a body of water, for transmitting coded pulses; and 
underwater receiver means for receiving the transmitted coded pulses, 
without any physical connection between the transmitter means and receiver 
means. 
The transmitter means includes a transmitter circuit for generating the 
coded pulses; and an underwater piezoelectric transducer for submersion in 
the water and electrically connected with the transmitter circuit for 
transmitting the coded pulses to the receiver. Preferably, the coded 
pulses are transmitted at a resonance frequency of the transducer. 
The transmitter circuit includes a shift register pre-programmed with a 
code corresponding to the coded pulses. Preferably, the code is a binary 
code, and the coded pulses are transmitted as ultrasonic pulses. 
The receiver means includes an underwater piezoelectric transducer, 
submerged in the water, for receiving the transmitted coded pulses; and a 
receiver circuit for comparing the received code pulses with stored coded 
pulses. The receiver circuit includes amplifier means for amplifying the 
received coded pulses, an internal clock generator for generating a clock 
signal, means for synchronizing the received and amplified coded pulses 
with the generated clock signal, and a shift register pre-programmed with 
a code corresponding to the received code pulses, and comparator means for 
comparing the received and amplified coded pulses with the code 
pre-programmed into the shift register, to verify that the received coded 
pulses correspond to the code pre-programmed into the shift register. 
In accordance with another aspect of the present invention, an underwater 
communication system by means of coded pulses, includes transmitter means, 
placed at a surface of a body of water, for transmitting coded pulses, the 
transmitter means having a transmitter circuit for generating the coded 
pulses, the transmitter circuit including first memory means 
pre-programmed with a code corresponding to the coded pulses, and an 
underwater piezoelectric transducer for submersion in the water and 
electrically connected with the transmitter circuit for transmitting the 
coded pulses through the water; and underwater receiver means for 
receiving the transmitted coded pulses, without any physical connection 
between the transmitter means and receiver means, the receiver means 
including an underwater piezoelectric transducer, submerged in the water, 
for receiving the transmitted coded pulses, and a receiver circuit for 
comparing the received code pulses with stored coded pulses, the receiver 
circuit including second memory means pre-programmed with the code 
corresponding to the coded pulses, and comparator means for comparing the 
received coded pulses with the code pre-programmed into the second memory 
means, to verify that the received coded pulses correspond to the code 
pre-programmed into the second memory means. 
In accordance with still another aspect of the present invention, an 
underwater communication system by means of coded pulses, includes 
transmitter means, placed at a surface of a body of water, for 
transmitting coded pulses, the transmitter means including a transmitter 
circuit for generating the coded pulses, the transmitter circuit including 
first memory means pre-programmed with a binary code corresponding to the 
coded pulses, and an underwater piezoelectric transducer for submersion in 
the water and electrically connected with the transmitter circuit for 
transmitting the coded pulses through the water; underwater receiver means 
for receiving the transmitted coded pulses, without any physical 
connection between the transmitter means and receiver means, the receiver 
means including an underwater piezoelectric transducer, submerged in the 
water, for receiving the transmitted coded pulses, and a receiver circuit 
for comparing the received code pulses with stored coded pulses, the 
receiver circuit including amplifier means for amplifying the received 
coded pulses, an internal clock generator for generating a clock signal, 
means for synchronizing the received and amplified coded pulses with the 
generated clock signal, second memory means pre-programmed with the binary 
code corresponding to the coded pulses, and comparator means for comparing 
the received coded pulses with the code pre-programmed into the second 
memory means, to verify that the received coded pulses correspond to the 
code pre-programmed into the second memory means; and actuator means for 
releasing a submerged object in response to verification by the comparator 
means that the received coded pulses correspond to the code pre-programmed 
into the second memory means. 
The above and other objects, features and advantages of the invention will 
become readily apparent from the following detailed description thereof 
which is to be read in connection with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings in detail, the underwater communication system 
according to the present invention includes a transmitter T, as shown in 
FIGS. 5a and 5b, within a seagoing craft, such as a boat. As shown in FIG. 
3, transmitter T is comprised essentially of a transmitter circuit 2, and 
a conventional 200 KHz underwater ultrasonic transducer 3 connected to 
circuit 2 and positioned just below the surface of the water. 
Circuit 2 includes a 12 volt DC battery supply 4 that is formed as part of 
transducer T or as part of the craft's battery supply, a timer 5 which 
powers circuit 2 for a few seconds, and two power stabilizers 6 and 7 that 
respectively power other 8 volt and 12 volt components of circuit 2. 
Circuit 2 further includes a 2 MHz quartz crystal 8, and a quartz 
oscillator 9 which is powered by stabilizer 6 at 8 volts and which is 
connected to an output of quartz crystal 8 to produce an oscillation 
signal with a frequency of 2 MHz. A frequency divider 10, which is also 
powered by stabilizer 6, frequency divides the 2 MHz output from 
oscillator 9 to a 200 KHz signal, that is, by a factor of ten. 
An internal clock generator 11 is supplied with the 200 KHz signal from 
frequency divider 10 and produces a 320 .mu.sec pulse signal with a 20.48 
msec pulse signal as an interval or period between the 320 .mu.sec pulses, 
in response to the 200 KHz signal. A reset 12 is connected with an input 
of internal clock generator 11, and has a logical AND function. Basically, 
internal clock generator 11 is a binary counter that generates the 
respective pulse times. When the counter reaches a desired value, reset 12 
operates to reset clock generator 11 and restart the count. For example, 
when the total period is 20.8 msec, that is, 20.48 msec plus 320 .mu.sec, 
reset 12 resets clock generator 11 every 20.8 msec. 
As an example, clock generator 11 can be a CMOS 4020B counter and reset 12 
can be a CMOS 4081B AND gate. In such case, a 200 KHz signal is supplied 
to the clock input at pin 10. Pin 2 produces a count 4096 (Q13) supplied 
to input A of the AND gate, while pin 6 produces a count 64 (Q7) at the 
input B of the AND gate. Specifically, a positive pulse is output from pin 
2 when counter Q13 is at a logic level "1" state and stays at this logic 
level "1" state for 320 .mu.sec, at the same time that the output from pin 
6 (corresponding to counter Q7) is at a logic level "1" state. At this 
time, the output of the AND gate at pin 11 is used as the reset, and 
restarts the counter from zero. 
Internal clock generator 11 sends the pulse signals as clock pulses to a 
clock counter 13. Clock counter 13 counts the clock pulses and when a 
predetermined count, for example, eight clock pulses, has been counted, 
supplies a control signal to a parallel in, serial out (PISO) shift 
register or converter 14 for the parallel loading of a preset code which 
is stored in shift register 14, with shift register 14 outputting the 
preset code in a serial manner in accordance with the clock pulses from 
clock generator 11. The preset code is pre-programmed with a selected key. 
Preferably, the preset code is a binary type code, where "1" represents a 
pulse and "0" represents the absence of a pulse, with the code being made 
from any number of bits, such as the eight bit 01001111 binary code (2F 
hexadecimal). For example, each pulse of the preset code has a duration of 
320 .mu.sec, with an interval between pulses of 20.48 msec. 
A pulse receiver 15 receives the coded pulses of the preset code from shift 
register 14 and sends these pulses, with a timing determined by the clock 
pulses from clock generator 11, to one input of an AND gate 16. A signal 
adapter 17 supplies the 200 KHz signal from frequency divider 10 to 
another input of AND gate 16, and also converts the 8 volts at the output 
of frequency divider 10, to 12 volts and supplies 12 volt power to AND 
gate 16. AND gate 16 performs an AND operation between the 200 KHz signal 
and the 320 .mu.sec pulse signal, and produces two signals with a phase 
shift of 180.degree. therebetween, each with a frequency of 200 KHz for 
320 .mu.sec. 
A buffer circuit 18 amplifies the signals, and sends the amplified signals 
to two power Darlington BD.times.53 transistor pairs 21', 21" through a 
series circuit of two capacitors 19', 19" and two trimmer resistors 20', 
20", respectively. 
The outputs of power Darlington transistor pairs 21', 21" are connected to 
opposite ends of the primary coil of a transformer 22, a center tap of 
which is supplied with 12 volts from stabilizer 7. Darlington transistor 
pairs 21', 21" work with a phase shift of 180.degree. to create a 
sinewave-like waveform from two inverted square waves with a phase shift 
of 180.degree., on the primary of transformer 22. In this regard, 
transistor pair 21' sends a saturation pulse to the transformer (top 
down). When the pulse from transistor pair 21' is ended, transistor pair 
21" sends a desaturation pulse (bottom up), so that the secondary of 
transformer 22 sees a single sine wave with a tension (peak to peak) value 
which is twice that of the original signal. 
As a result, there is a voltage of 24 volts across the primary coil of 
transformer 22. The secondary coil of transformer 22, in turn, provides a 
voltage of 300 volts, such that transformer 22 increases the voltage from 
24 volts to 300 volts. 
Accordingly, a 309 volt signal having a frequency of 200 KHz during pulse 
durations of 320 .mu.sec of a preset code, with an interval or period 
between pulses of 20.48, msec is supplied to ultrasonic transducer 3, 
which transmits the coded pulse signal to a receiver R. 
In a preferred embodiment, receiver R is connected to a release actuator A 
for the recovery of a submerged object S, as shown in FIGS. 5a and 5b. 
Receiver R includes a receiver circuit 23 and an underwater transducer 24. 
Circuit 23 includes a 2 MHz quartz crystal 25, and a quartz oscillator 26 
which is connected to an output of quartz crystal 25 to produce an 
oscillation signal. A frequency divider 27 frequency divides the 2 MHz 
output from oscillator 26 to a 200 KHz signal, that is, by a factor of 
ten. 
An internal clock generator 28 is supplied with the 200 KHz signal from 
frequency divider 27 and produces a 320 .mu.sec pulse signal with an 
interval or period between pulses of 20.48 msec, in response thereto. A 
reset 29 is connected with an input of internal clock generator 28, and 
has a logical AND function. Basically, internal clock generator 28 is a 
binary counter that generates the respective pulse times. When the counter 
reaches a desired value, reset 29 operates to reset clock generator 28 and 
restart the count. For example, when the total period is 20.8 msec, that 
is, 20.48 msec plus 320 .mu.sec, reset 29 resets clock generator 28 every 
20.8 msec. 
A monostable multivibrator or one-shot timer 30 receives each 320 .mu.sec 
pulse from clock generator 28, and produces a 2 msec signal in response 
thereto. 
An amplifier 34 amplifies the signal received from transducer 24, and 
supplies the amplified signal through a capacitor to an integrated circuit 
of a signal digitizer 33, that is, an analog to digital converter. A 
second monostable multivibrator or one-shot timer 32 receives the 
digitized signal from circuit 33 and, through an integrated circuit 31, 
powers oscillator 26 and frequency divider 27 for a period of 2 seconds 
upon receipt of the first pulse of the received signal. In this regard, 
the clock signal that is generated by receiver R is synchronized with the 
received signal. 
The output of digitizer circuit 33 is also supplied to a third monostable 
multivibrator or one-shot timer 35 that receives the 320 .mu.sec pulse 
signal and widens it to 18 msec. 
A serial in, parallel out (SIPO) shift register 36 which is pre-programmed 
with the same key or code as shift register 14 of transmitter T, receives 
the 18 msec pulse signal from monostable multivibrator 35 and the 2 msec 
clock pulse signal from monostable multivibrator 30, and in response 
thereto, produces the received code. In other words, when both signals are 
received by shift register 36, an "open gate" condition occurs. 
As a result, the received code is supplied by shift register 36, along with 
the preset code, to two integrated circuits or comparators 37 and 38 in 
order to match the received code with the preset code. The reason that two 
comparators 37 are used is that each comparator 37 and 38 is a commercial 
4 bit comparator, while shift register 36 produces an 8 bit signal. 
Therefore, it is necessary to use two comparators to decode the 8 bits. 
An integrated control circuit 39 generates a control pulse if the code 
verified by circuits 37 and 38 is correct, that is, is the preset code. If 
the preset code is correct, a signal indicating the same, that is, a "code 
is OK" signal, is supplied to an integrated verifying circuit 40. To avoid 
any errors, circuit 40 verifies several times that the "code is OK" signal 
has been sent by circuit 39, and sends a signal acknowledging the same to 
a monostable multivibrator or one-shot timer 41. Monostable multivibrator 
41 generates a pulse of sufficient length to operate a DC motor 44 that 
controls actuator A of FIGS. 5a and 5b to release underwater transducer 24 
and allow receiver R to float to the surface of the water. A buffer 42 is 
connected between monostable multivibrator 41 and DC motor 44 to prevent 
DC motor 44 from being operated more than once for each sequence of 
received pulses. 
DC motor 44 includes a built-in rpm divider and is powered by a battery 46 
through a MOSFET 43. An integrated charge checking circuit 45 checks the 
charge of battery 46, and sends a forced release control to ensure that 
receiver R is released to the surface when the charge of battery 46 is too 
low. 
Although the above embodiment has been described in regard to a device to 
pilot a release, the invention can be applied to other uses. For example, 
the same receiver can translate the received signal to displayed pulses, 
so as to provide visual information or coded characters to a scuba diver, 
keeping him in touch with the craft that has the transmitter. At the same 
time, the scuba diver can transmit a coded pulse signal to the craft to 
provide bidirectional wireless communication. 
Further, although a binary code is transmitted, ASCII characters or other 
commands can be sent by adding appropriate circuits. In such case, the 
receiver will recognize and display the characters received after the key 
or perform appropriate actions. This latter arrangement is very useful as 
a means of ship to ship, or ship to submarine underwater communication. 
Having described specific preferred embodiments of the invention with 
reference to the accompanying drawings, it will be appreciated that the 
present invention is not limited to those precise embodiments and that 
various changes and modifications can be effected therein by one of 
ordinary skill in the art without departing from the scope or spirit of 
the invention as defined by the appended claims.