Instruction manual

WCT3  8
“+4.5V” voltage is referenced to the signal ground and not the power ground.
If a reading is taken between the power ground and signal ground with refer-
ence to the signal ground you will see a reading of “-4.5V”. So the difference
between the “+4.5V” and “-4.5V”, (measurements referenced to signal
ground), points of the circuit is now +9 volts with reference to the power
ground.
A Little More About Wireless Remote Control Signals
Here’s a little more information about how most wireless remote control sys-
tems work and how the WCT3 detects the signals. The 315/433MHz, 125KHz
and 20KHz sections of the WCT3 will detect the presence of virtually any sig-
nal that is within the design frequency range. It doesn’t matter if there is data,
modulation, on the signal or not. The simple presence of the signal will be
indicated. The infrared section operates in a slightly different way. We’ll take
a look at the circuit operation differences here.
When you see the indicator flashing when you activate any wireless remote
control you are seeing the modulation signal. Most remote controls, both RF
and infrared type systems, modulate the signal by turning the signal on and
off. This is often referred to as OOK, O
n-Off_Keying, modulation. When the
indicator flashes you are seeing the result of the modulation. Actually an un-
modulated signal is constantly turning on and off at the frequency of the un-
modulated signal. This unmodulated signal is called the carrier, (i.e. it carries
the data). The frequency of the carriers, except for the infrared, detected by
the WCT3 are 315MHZ, 433MHz, 120KHz and 20KHz. If the indicator does
not flash but simply stays on that indicates that the signal is not being modu-
lated and only the fact that a signal in the proper frequency range is present.
(Actually the indicator may be flashing or flickering but it is so fast that your
eyes think it’s on all the time, but that’s beyond the scope of this manual.)
The infrared section also indicates the modulation by flashing but it will not
provide an indication if the signal is not modulated. That’s because the fre-
quency of the infrared carrier is so high that Q1 simply turns on and turns off
when light is present and removed. The detector section actually detects only
the 38KHz carrier signal. You can think of Q1 as both the antenna and filter
part of the “Input/Filter” section of the infrared section. This means that virtu-
ally any infrared or light signal will be indicated by the WCT3 as long as it is
modulated so you can use it to test any virtually any remote that uses infrared
and a carrier signal.
An interesting experiment you can try is to use the WCT3 to detect movement
of a light source or of an object moving between the light source and WCT3.
If you point the infrared detector of the WCT3 toward a light source you may
see a brief flash of the IR indicator. By simply moving your hand between the
light and WCT3 rapidly you will see the indicator flicker or even stay on if you