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3

The TIP120 is possibly the worst transistor you could choose for this job. It is a Darlington Pair transistor, and those have a (relatively) massive forward drop of between 2 and 4 volts. It works with the LED because an LED needs a tiny amount of current to operate compared to the motor and has a fixed forward voltage of its own. The motor doesn't, and is ...


3

So you want to use the 5V voltage regulator on the Arduino serve as the supply for your 5V components, and feed the 5V regulator from the 12V supply that powers your solenoid? The problem with that plan is heat. The voltage regulator on the Arduino is a poorly heat-sinked (heat-sunk?) "linear" regulator. A linear voltage regulator is basically a solid state ...


2

If the sensor does provide two defined voltage levels, you do not need a pullup or pulldown resistor, but if it's only a switch: either (closed) connected to Vcc or GND, or (open) not connected, you need a pullup or pulldown resistor to get a defined voltage level in case there's "nothing else" (except the wire to the switch catching noise out of the air) ...


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I realize that power is flowing the entire time the switch is open, which may (or may not) drain the battery. No, it doesn't. You get a small spike as the switch is opened or closed, as the gate capacitance is charged or discharged, but other than that there is negligible current draw by a pin, which remains static regardless of the direction of the biasing ...


2

The input current does not depend on the pin level. Have a look at this discussion from avrfreaks. The input impedance of a digital pin is extremely high. The leakage current of the Atmega328P (here as example chip) is mentioned to be 1uA for both pin states. So this current is both unavoidable and neglectable from a normal view. But the input impedance of ...


1

Does this mean that even with the external power supply the Arduino will be connected to the UGND, and in effect the protective earth? Yes. Would it be ok to remove the jumper connection between UGND and GND? No. I don't know quite why they provided that jumper. I can see no scenario in the datasheet where it suggests the two can be separate. Or ...


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You can use the adapter because: the adapter uses an AMS1117 to generate 3.3V to supply the SD card and the level shifter the level shifter is a 74LVC125 which uses 3.3V and works with 3.3V (and accepts up to 5V as input level) The adapter works for 3.3V and 5V systems as long as 5V power is available.


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