If a digital input is set HIGH and the voltage is allowed to diminish, it triggers LOW at 1.1V?
And if set LOW and the voltage allowed to increase, it triggers HIGH at 3.3V? Do I have those right?
And they read fast. And
Arduino (Atmega) pins default to inputs, so they don't need to be explicitly declared as inputs with pinMode(). Pins configured as inputs are said to be in a high-impedance state. One way of explaining this is that input pins make extremely small demands on the circuit that they are sampling, say equivalent to a series resistor of 100 megohm in front of the pin. This means that it takes very little current to move the input pin from one state to another, and can make the pins useful for such tasks as implementing a capacitive touch sensor, reading an LED as a photodiode, or reading an analog sensor with a scheme such as RCTime.
If you put 300 megohm between 5V and the pin, would that read as 1.25V?
But the line has to see more than the trigger state for HIGH to not read LOW.
So what if you connected to the same pin a small resistor, a small cap and ground the before reading the pin, you did a HIGH output to load the cap and then switched to input... something like when reading a led?
I think that the right RC should power the line enough to start the read as HIGH and that until Vcc falls enough the pin should read HIGH at least with the right resistor between Vcc and the pin.
That should allow monitoring Vcc without using serial Rx or Tx.
BTW, how much backup can I get using a thin plastic jar inside a thick glass jar with electrodes and water....
and only feeding it 5V? Or maybe there's a way to get 5V using 2.5V caps? They don't add V in series do they?