Instruction manual

WCT3  7
is a spiral circuit trace near the ANT1 connection on the left side of the board.
You will also notice that the detector diodes D3 and D4 are a different type.
This is because of the much higher frequency we are working with. The diode
package used on the other sections will not function at these frequencies.
The Infrared section of the WCT3 is the least critical section even though the
infrared signal is near the frequency range of visible light. This is because the
device that captures the infrared signal, Q1, easily responds to signals in the
frequency range of light. Q1 is called a photo transistor which acts like a
switch and turns on when it ’sees’ infrared or light. The infrared signal from a
control is turned on and off, modulated, so Q1 actually turns on and off at the
rate of the modulated signal. The frequency of the modulation is typically in
the range of 38KHz and is therefore extremely easy to work with. You can
think of Q1 as the antenna and filter, and the detector is actually detecting the
modulation signal rather than the actual infrared signal.
The amplifier and comparator stages of all the sections are identical in opera-
tion with the only differences being in the amplifier stage gain and comparator
reference levels. Each of these areas is designed specifically for the charac-
teristics of signal to be detected.
Power Supply Operation
Power for the WCT3 is provided by a standard 9V battery. Looking at the
power supply section of the schematic you will see the battery on the left.
When push button switch S1 is pressed power is applied to operate the
WCT3. Capacitor C3 is a filter which insures a stable 9 volts under sudden
heavy loads, such as when an LED lights. It acts like a big reserve reservoir
for sudden power surges.
Now you are asking why the voltage connection after switch S1 is labeled
“+4.5V”. Good question. You will notice that there are two types of ‘ground’
connection symbols used in the schematic. One is a simple triangle and the
other is a triangle made up of three parallel lines. Notice that the ‘-‘ connec-
tion of the 9 volt battery as well as the, ‘-‘ lead of C3, Pin 11 of U1-D and U2-
D, and one lead of R7 and R22 are connected to the triangle. If a measure-
ment is taken with reference to this ground connection a reading of +9 volts
will be seen. This is actually the power ground reference but is not the signal
ground reference point used for the detected signals.
The ground connection indicated by the other triangle symbol is the signal
ground reference. Resistors R22 and R23 are used to create a reference
point half way between the 9 volt supply and power ground that supplies
power to U1 and U2. This allows the amplifier and comparator to accept a
signal that swings between a positive and negative level with reference to the
signal ground point which is the connection between the resistors. The