Re: TDA2822 Audio problem #ubitx #tda2822

Jerry Gaffke

Given all the different Raduino's getting built, seems reasonable to 
just build one without the 12mhz and 16mhz oscillators.
This could be plug and play, an easy solution for the now thousands of uBitx's out in the field.

Some digital modes will want a USB interface while operating the radio.
But much easier to get rid of 12mhz nasties if the radio only sees 9600 baud UART lines
from an FTDI/CH340   UART-to-USB   cable assembly.

On Mon, Apr 9, 2018 at 09:50 pm, John Backo wrote:

12 MHz is necessary for ANY USB interface.

The 12 MHz xtal on the radiuno drives the CH340
chip. It cannot be disabled (or changed very much)
and have USB work anynore.

Similarly, any other chip connected, FTDI or whatever, has
to have the 12 MHz to operate.

It is easy to build a Si5351 board with an Adafruit board
or whatever, and drive it with a bread-boarded ATMega328P
which does not have a USB interface. Then only the mcu xtal
would possibly be a source of interference. Generally, I do not
think this is the case. In any event, almost any xtal up to about 20 MHz
could be substituted and the mcu would work. If it is the source
of birdies (or whatever) they should shift substantially.

It could very well be that the 12 MHz xtal is the source of some birdies,
but the proper method is to isolate and possibley ground the output of the
CH340 chip under some conditions. It is always active, even when a USB
connection is not being used.


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