---Figure 1-6 Assembling fhe hydropholle or sending
IIIlif
Chapter One
used in conjunction with the 10K-ohm potentiometer at RS. TIle electret microphone electronics can be mounted on a small circuit board. Remember to observc the correct polarit), when installing capaci-tors and the op-amp. to ensure that the circuit will operate properly when power is applied.
llie transducer or pre-amp board lind tbe ampli-fier board are connected via a length of call.'\: cable.
Now. you will need to determine the length of cable you will need between the microphone transducer and the amplifier board that
will
best suit yourpartic-ular application. You might wish to start with a 15- to 20·(00t cable length between the transducer and
amplifier boards. Next. you will need a small plastic film canister: drill a hold to pass the coax cable
through the lOp of the
mill
can. De sure to drill thehole for the call.'\: cable undersized, so it will be a tigbt
fit.
Pass the transducer end of the coax through theCable to surface
Audio cable, 2-conductor with shield, Radio Shack pn 278·513 or equi\l
Hal melt glue 10 seaVcanisler joint (both sides 01 lid)
Silicone RTV blob over end of cable acls as a walerblock to keep oil from squishing up inside althe cable as waler pressure increases with deplh
Interior filled with vegetable oil :::-_- - Heal-shrink over solder joints
_ - - - Piezo microphone
_ and pre-amplifier assembly
~--- PlasUc film canister
Figure 1-7 Assembling fhe hytlropllOlle or sendillg /fllif
S ound Energy 11
o ::3
ro
I
I
(l) s::
o
R6 R7
C2
Figure 1·8 Hydrophone pre-(lmplifier circuit
top of the film canister (refer again to Figures 1·6 and 1-7). Next. solder the cable 10 the transducer or
sender board. and then secure the electronics board in the film can so that it docs not rattle around inside the can. Fill the canister with light mineral oil ncarly to the lOp of the container. Locate some silicone
sealant or room-femperatllre \l1//c(lIIizillg (RTV)
sealant and run a bead all around the coax cable on both sides of the film can lOp cover. Place the top of
the film can over the film can and secure it 10 the can.
And finally. run a bead of silicone all around the top cover of the canister.
AI the opposite end of the transducer cable. you will want to attach some Iype of connector such as a
lIs -inch mini audio connector that will mate to a phone jack on the electronics amplifier chassis box.
The hydrophone main amplifier board shown in Figure 1-9 centers arollnd the LM380, a 2.S-watt audio power amplifier. The shielded cable from the microphone pre-amp connects to a screw terminal strip. Actually, any three terminal connectors set may be used instead. Terminal A is the 12-voit bias to
power the electret microphone. Terminal B is the actual audio output signal from the microphone pre
-amp 10 the main amplifier input. Terminal C is the system ground connection between the microphone pre-amp and the main amplifier. The audio output from the pre-amplifier board is fed to the main audio amplifier through capacitor CI. The output from C I
is immediately coupled to a 50K-ohm potentiometer.
which is secondly coupled to the op-amp through capacitor C2. a 2.2 uF electrolytic capacitor. The output of the audio amplifier is conditioned by the
resistive and capacitor network of R3 and C4. The 8-ohm speaker is coupled to the amplifier through capacitor CS.
Note. that the hydrophone is powered by the coax cable from the Il-voh battery through switch Sl:a.
-The remote audio power amplifier is also powered by the 12-\'011 battery. Pins 3.4. 5. 7. 10. 11. and 12 arc all tied to ground on the circuit board. Construction of the main hydrophone amplifier is constructed on a small glass epoxy circuit board. You could also elect to construct the circuit on a perf-board if desired.
When assembling the main hydrophone amplifier,
(1)' and locate an integrated circuit socket for the LM380 amplifier. Be careful to observe the correct polarit), of all of the capacitors during installation.
12 Electronic Sensors for the E vil Genius
12 Volt
+
B1
S1:a S1 :b
14 +
C6
A B
C2 6 10
+ 11 12 C5
8 + S2
C
U1
2 5 +
+ 4 J1
2 C4
C1 1
Speaker +
R1 C3 R3
Figure 1-9 Hydroplwl/{' amplifier cirellil
\\'hen installing the integrated circuit. you must be provide a decent amount of current to power the e ir-sure 10 inser! the part correctly to avoid damage to cuit for a reasonable period of time.
the circuit. lntegrated circuits arc always marked with The hydrophone muy be used as a fish finder by either a small indented circle to the right of pin 1 or mounting it on a pole or handle so you cun hold it wilh a rectangular cutout at the top center of the Ie
package. After installing all of the componcnts on the circuit board. be sure to look for cold solder joinls.
shorts. and SlnlV wire leads left on the board after trimming componenl leads.
The main hydrophone amplifier circuit is hOLL<;ed in it j
x
7 x ?-inch aluminulll chassis box. The IWOtoggle switches SI and S1. the volume conlrol. and the input jack al J I are all moullIed on the front
panel of the chassis box. The headphone jack at J2 is mounted on the rear panel of the enclosure. In order
10 supply power to the hydrophone circuils. it is
<ldvisable to usc J four-cell AA plastic ballery hold -ers. which can be mounted to the lOp cover of the aluminum chassis box. The eight AA b<ltteries will
Chapter One
over the edge of a slllall bO<lt or seawall. A piece of electrical conduit or a bamboo pole can be used. Fla t-ten the conduit on the end to go into the water so you can mount and tape the unit to it. Be sure not to
cover the nat surface of the unit with tape to assure maximum sensitivity to sound while in Ihe water. Use a hose clamp. lacing twine. or electricallape to allach
the hydrophone to the pole. If you want to run your hydrophone down to greater depths. 50 to 300 feet or so. be sure 10 use shielded cable the whole length of
the run to avoid picking up 100 much hum from any local power lines. Solder all electrical connections you make and apply sufficient silicone rubber and electrical tape to all connections to assure lasting
waterproof conneclions and splices.