voltage
2 pages across tutorials, modules, pinouts and guides.

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INA219 Current Monitor
A 100 milliohm resistor in the positive wire and a chip that reads the millivolts across it. Current, voltage and power over I²C, up to 3.2 A on a rail of up to 26 V.

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Voltmeter
A 30 kΩ and 7.5 kΩ divider behind a two-screw terminal: SIG is exactly one fifth of the input, so an analog pin can read up to 25 V on a 5 V board and about 15.5 V on a 3.3 V one. DC only, measured from GND.