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Well, I ended up answering my own question in a few minutes of forum research. You can disable the TX pin of the hardware UART with: UCSR0B &= ~bit (TXEN0);


A good practice is to set the pin mode for all the pins used by the sketch. void setup() { Serial.begin(115200); while(!Serial); pinMode(34, INPUT); pinMode(35, INPUT); pinMode(36, INPUT); pinMode(37, INPUT); pinMode(LED_BUILTIN, OUTPUT); Serial.print("Test"); } The Arduino AVR core does set the pin mode to INPUT by default ...


The normal way is to use a P-channel MOSFET as a "high side" switch. simulate this circuit – Schematic created using CircuitLab R1 keeps it switched off under "normal" circumstances. Driving D4 LOW makes M1 turn on and allow power through to the "component". Make sure that the MOSFET has a threshold voltage of no more than (less than?) -3V (that is,...


Pretty sure RST is Reset input to the CP2102, that will not work. DTR to DTR (BLK on the Promini) will work, the DTR Low level goes thru the Promini's 0.1uF cap and 10K Reset pullup resistor to make a Reset pulse. That's how the FTDI Basic works when connected. RTS (Request To Send output) might also work, that is supposedly a pulsed level.


RST to RST. Ignore the others, they are irrelevant.

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