@gunrunnerjohn posted:There's also a maximum total current on all the pins I suspect, I can't imagine the Arduino processor will handle 40ma on every I/O pin.
The maximum total current sourced or sinked by the chip is stated as 200mA on the 328p datasheet. However, the notes suggest that you have to pay attention to current per port if you expect the rated current or voltage to be delivered on a particular pin:
3. Although each I/O port can sink more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steady state conditions (non-transient), the following must be observed: ATmega328P: 1] The sum of all IOL, for ports C0 - C5, should not exceed 100mA. 2] The sum of all IOL, for ports B0 - B5, D5 - D7, XTAL1, XTAL2 should not exceed 100mA. 3] The sum of all IOL, for ports D0 - D4, should not exceed 100mA. If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current greater than the listed test condition.
4. Although each I/O port can source more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steady state conditions (non-transient), the following must be observed: ATmega328P: 1] The sum of all IOH, for ports C0 - C5, D0- D4, should not exceed 150mA. 2] The sum of all IOH, for ports B0 - B5, D5 - D7, XTAL1, XTAL2 should not exceed 150mA. If IIOH exceeds the test condition, VOH may exceed the related specification. Pins are not guaranteed to source current greater than the listed test condition.
