LBC6K
•
5
PWM signal which has an encoded signal in it. The bottom signal is the
decoded PWM of the middle PWM signal. Note how when there is a lot of on
time (high) on the PWM signal, the resulting decoded signal is higher, and
when there is a lot of off time (low) the signal is lower.
The receiver module of your LBC6K is pretty simple. It consists of a very
sharp low-pass filter at 6kHz and an audio amplifier. The filter is sharp to
reject the 18kHz PWM clock, but let the audio encoded from 6kHz on down
through. 6kHz and below is perfect for transmitting voice signals.
Below you can see the various stages of filtering in the receiver. The top
trace is the unfiltered received PWM signal right at the collector of Q1 (the
signal is small, but this is what it looks like). The middle trace is after the first
stage of filtering, which is close to what you would see on pin 14 of U1.
Notice how even through it has the 18kHz signal on it, it more closely
resembles the final filtered output of the bottom trace, which is seen at pin 7
of U1.
The receiver is a bit more complex and many of the more complex parts are
contained in the microcontroller. The microcontroller (U3) performs the AGC
Содержание Laser Beam Communicator
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