DIY HYDROPHONE
ELECTRONIC CIRCUITS
Watlington's Pre-Amp Circuit
Pre-amp and Amplifier
Physical Layout
LM380 Amplifier Circuit
My Squelch page also includes a circuit
relevant to hydrophones
Frank
Watlington's Pre-Amp Circuit
The above pre-amp circuit is the one I use with both dunking and towing
DIY hydrophones. The left hand side is potted in epoxy and housed with the
hydrophone Piezo element. The right hand side is on board the boat, but linked
to the hydrophone via the cable. The output of this pre-amp circuit needs
further amplification before it can be heard in a very small loud speaker or
headphones. For loudspeakers
a third stage of amplification is required.
The diagram below shows the physical layout and components for a dunking
hydrophone using the above pre-Amp, and to minimise the amount of electronics involved, assumes that an
off-the-shelf amplifier (see
links) will be used to boost the pre-amp signal to a high
enough level to be audible in headphones, or an earphone. Below this is a circuit
for such an amplifier based on the LM380 Chip,
which is not difficult to build, and is what I actually used in my first
hydrophones.
Link to list of Components with Jaycar Part numbers in
html
format
Link to list of Components with Jaycar Part numbers in
Word
format
Simple Amplifier Circuit
The Amplifier Circuit reproduced below is from the "Dick Smith
Electronics" catalogue (Australia) and is the one that I used for my first DIY
hydrophones. The output from the pre-amp circuit was connected as the input to
this circuit, and the audio output from this amplifier circuit was
connected to a mono headphone rather than the 8 ohm speaker shown in the
catalogue circuit. This and the pre-amp can be powered from a single 9 Volt dry
cell battery, or from a boat's 12 Volt supply. The 12 Volt should be regulated
(to 9 or 12 Volts) using a voltage regulating chip if the system voltage could
exceed 15 Volts. The LM380 chip and regulating chips are commonly available from electronic hobby
supply stores, as are the resistors and capacitors, and piezo buzzers from which
the ceramic piezo element can be removed.
Making a PCB
The electronics for these little circuits can be readily soldered
together using project boards pre-drilled with a matrix of small holes, with or without
copper around the holes on one side of the boards, and short insulated wire links. Electronic
hobby shops also offer blank PCB with a copper layer all over one side. These
can be used to make circuit boards by etching away the unwanted copper to leave
just the tracks needed to interconnect the components. The result is a neater
project. I did this for the above amplifier circuit, incorporating
locations for a voltage regulating chip and and my first attempts at a squelch
circuit. The circuit was not a success, but the method of producing a PCB
from artwork was satisfactory, despite my amateurish artwork.
There are various ways to do the etching, but I used a laser printer to transfer
my layout artwork onto
"Press-N-Peel" film. The film was then ironed onto a piece of blank
copper PCB, leaving a plastic version of the artwork adhering to the
copper. The board was then etched in Ammonium Persulphate to remove the exposed
copper, after which the plastic protecting the circuit was peeled off to
re-expose the copper circuits.
The photo shows the final step - drilling holes for the components in the PCB.
I used CorelDraw to prepare my artwork, which isn't designed for that job and
was a laborious process.
PCB Layout Programs
I've since tried several shareware programs that can be used to produce
artwork for small PCBs. EagleCad was the
most sophisticated that I came across, with the largest library of standard
components. It was recommended to me by Ricardo Paez in Chile, who
successfully built one of my DIY hydrophones, and then added a short range
FM wireless link to it, so that other students on the boat could tune in the
hydrophone on their portable radios. His PCB layouts look professional, but
I found EaglkeCad procedures counterintuitive, and without a tutorial I
couldn't make practical use of it.
ExpressPCB is one of many programs available from specific board
manufacturers, and was used to produce the schematic in my
Squelch page. I found it easier to get to
grips with, but its small library of standard components meant I had to
draw many components manually, with distinctly unprofessional looking results!
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