QRP Labs QCX 5W CW, Руководство по сборке

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QCX assembly Rev 1.08
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5.13 Microcontroller
The ATmega328 microcontroller circuit controls many aspects of this transceiver. Below is this
section of the transceiver circuit. Several points are worthy of discussion.
ATmega328P processor
The ATmega328P was chosen because it has enough processing power and I/O to handle all the
tasks required here. It is also common and inexpensive, and lots of QRP Labs products already
used it, bringing economies of scale in both the kit preparation and the coding. The processor is
operated at its maximum rated 20MHz system clock speed.
The code is all written in C and is not open source. While the same ATmega328 processor is used
in the popular Arduino Uno products, there is no relation between code written for the Arduino
environment and the custom code written for this CW transceiver.
Tuning clicks
Some constructors of radio receiver projects that use the Si5351A report loud clicks every time the
frequency is changed. The cause of these clicks is one or both of two underlying issues:
a) Faults in the software configuring the Si5351A
b) Power line or radiated noise from the microcontroller/LCD back into the sensitive receiver
The first of these is not an issue here since we have already extensive experience using the
Si5351A and have perfected its configuration.
The second issue is important to address. Every time the microcontroller updates the Si5351A
configuration to cause it to change frequency, it typically also writes the new frequency to the LCD.
There is a burst of activity in the microcontroller, and on the digital control signals to both the
Si5351A and the LCD. The LCD controller chip will also be doing some work to effect the changed
display. All of these digital transitions can radiate noise into the receiver front end. Changes in
power consumption cause noise on the supply lines which can also be converted into noise
detected in the receiver front end.