05-05-2012, 01:44 PM
ONE-WAY AUDIO BY FIBER OPTIC CABLE
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ASSEMBLY INSTRUCTIONS
First of all check off the components against the
Component Listing on the next page. Especially make sure
to get the resistors correctly identified.
Note that the FO emitter & detector modules are very
similar. The detector which goes on the receiver board has
a red dot marked on its black case. The emitter which goes
on the transmitter board has a pink dot on a blue case. The
components for both boards are mixed together. Make one
board at a time. Look at the circuit schematic diagram,
identify the component then place it in the board. It is
generally best to add the lowest height components first.
So place the resistors first.
CIRCUIT DESCRIPTION
The voice signal begins as a sound wave. It is converted
to an electrical signal by the electret microphone in the Tx
circuit. This signal is amplified by the LM358 audio
amplifier and converted to an optical signal by switching
the voltage to the LED via a signal transistor. This optical
signal is fed into the plastic fibre optic cable.
At the other end of the cable the optical signal is directed
at a photodarlington in the receiver which converts it to an
electrical signal again. The signal is amplified and fed into
a speaker where it becomes a sound wave. A voltage
regulator has been used in the circuit to overcome
feedback in the circuit.
WHAT TO DO IF IT DOES NOT WORK
Poor soldering is the most likely reason that the circuit
does not work. Check all solder joints carefully under a
good light. Next check that all components are in their
correct position on the PCB - the IC's, and the electrolytic
capacitors. Thirdly, follow the track with a voltmeter to
check the voltage at various parts of the circuit. Did you
prepare the ends of the cable properly and insert it into the
transmitter LED & receiver unit correctly.