GaryY:
My animatronics project will use 3 or 4 servos, several SSRs for LED drivers & other peripherals.It looks like the Uno can drive 5V @ 40ma per pin, but not to exceed 200mA total for all pins.
Arduino output pin current ratings do not mean anything in the context of driving servos as the output pins just carry the pwm logic control signal and there will be almost no current required by the servo's control input.
The 9g TowerPro SG90 microservos do not specify rated current VS speed / torque . I have 2 servos running direct drive eyeballs from an UNO as a test, so far havent failed anything. Is there a rule of thumb available about driving servos loads ?
My personal 'rule of thumb' is to always use an external regulated +5vdc power supply to wire to the power wire of any and all servos, and allow one amp of power supply capacity for each servo you plan to drive. You also have to wire this external supply's ground to an arduino ground pin.Does it make sense to supply servo power separately and just use the PWM output ? ( making sure both supplies reference the same common )
Again the PWM output has nothing to do with the power requirement needed by the servo. A servo has 3 wires, one for +5vdc power, one for a PWM control signal, and one ground wire. The servo power requirement issue has nothing to do with the arduino's PWM output pin.
The 3.3 V power supply specs 50mA available, hopefully enough to power a WTV020-16P audio player.
Check a datasheet for the audio player, it should give you such information about its power requirements. Also older arduino boards had the 50ma 3.3vdc limit as the power came from a very small regulator inside the FTDI USB serial converter chip. Newer boards like the Uno use a dedicated on-board 3.3vdc voltage regulator chip that can provide much more then 50ma of current.
The Mega2560 has alot more IO , still has 40mA per pin limit, and the 5V voltage regulator chip NCP1117ST50T3G is spec'd at 1A max , but with a caveat that it can do 1500mA but may thermally protect itself.
Output pin current draw is not the issue with servos, it's the total current being drawn from the 5V shield pin, which is the +5vdc voltage source coming from either the USB connector (with a 500ma max rating) or the on-board +5vdc voltage regulator if you are using the external power connector (with a somewhat less then 1 amp max rating).
Can the Mega2560 circuit board traces and connectors handle 1 A steady state ?
Yes, but current limit is based on USB or voltage regulator not traces or connector pins.
Lefty