Re: uBITX CW - digital input?

Jerry Gaffke

The Nano pin used for the keyer input is an analog only input,
there is no digital IO cell in the processor silicon at that pin and thus no pullup resistor available.

The schematics are a bit confusing as connector names are not given and pin numbering is not consistent.
However if you count the pins and check the positions of the ground power pins, you can generally figure it out.

The uBitx wireup diagram is at the top of this page:
Your keyer plugs into connector J1 shown in the lower left, goes into pin 2 of the Raduino 8 pin connector,
and pin 3 is +5v, pin 4 is ground.

The Raduino schematic here:
shows that P1 pin 2 goes into the A6 pin of the Nano processor.

The Arduino Nano-CH340 clone schematic:
shows that A6 goes into ADC6 on pin 20 of the Atmega-328P-32TQFP processor chip.
Note that ADC0 through ADC5 of the chip are also named PC0 through PC5, indicating that those
analog inputs can also be digital IO pins.  But ADC6 and ADC7 do not have a PC6, PC7 designation,
since they are analog only.  And that pullups are only implemented on pins with digital IO.

The datasheet for the Atmega-328P verifies that pins ADC6 and ADC7 are analog inputs only.

Jerry, KE7ER

On Thu, Oct 24, 2019 at 05:31 PM, Rob French (KC4UPR) wrote:
Is there any reason I can't switch the existing uBITX Raduino CW input pin to be digital, INPUT_PULLUP? Obviously it could only be used for straight key in that case, but would it work? I would assume the external pull-up would no longer be required?

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