In Lab 7 you constructed the transmitter and receiver circuits (up to
the non-inverting amplifier) including
the transmit and receive coils as shown in Figure 
.
Figure: Transmitter and Receiver Circuit
The whole system will be integrated in Lab 9. In this lab you will test the
sub-circuits of both the transmitter and receiver, as well as the
composite system from system input to the output of the rectifier.
The system (up to the non-inverting amplifier, with no
connection between the receiver and the non-inverting amp)
will operate as follows. The function generator
will supply a high frequency sinusoidal signal at the input to the
transmitter. When the SPST switch is closed, current will flow through the
LED as well as the transmitting coil through the 1 k
potentiometer.
The LED will be illuminated and its intensity will indicate the relative
signal strength of the function generator. The 1 k
potentiometer
will be used to adjust the strength of the signal applied to the transmitting
coil. The current through the transmitting coil will induce a voltage
across the receiving coil according to Faraday's Law of mutual inductance.
Since the transmitted signal is sinusoidal, the induced voltage across the
receiver coil will also be sinusoidal at the same frequency as the
transmitted sinusoid. As will be explained in the following section, a
diode acts as a one-way valve allowing current to flow easily in one
direction and strongly opposing current in the other direction. The
silicon diode in the receiver will allow current to flow through it
to the right but not to the left. The arrow head in the diode symbol indicates
the forward direction. Current flows easily in the forward
direction but not in the reverse direction. When the sinusoidal voltage
across the receiver coil is positive, current will flow through the diode in
its forward direction and charge the capacitor 
at a rate dictated by
the time constant 
. When the sinusoidal voltage
across the receiver coil is negative, the diode will cease to conduct since
the voltage across the receive coil is trying to force current in the
reverse direction of the diode. Hence, when the voltage
across the receiver coil is negative, no current flows through the diode,
and the capacitor will discharge through 
according to the
time constant 
. If the time constant 
is significantly greater than the period of the sinusoidal voltage across the
receiver coil, then the capacitor will not have time to discharge before the
next positive half-cycle comes along and tops off its charge. The result
is a conversion of an AC (sinusoidal) signal to a DC (constant) signal.
The DC signal level across the combination of 
and 
will be
proportional to the transmitted signal strength provided that your
transmit and receive coils do not move during transmission. The DC
signal level produced in the receiver across the combination of 
and 
will be too low to drive the servo controller. However, you will design
and build an op-amp non-inverting amplifier to obtain the needed voltage
gain to drive the servo controller. Your goal, when the system is completed is
for your circuit to be able to control the servo over as much of its range as
possible while adjusting the 1 k
potentiometer in the transmitter.