What is the max current available from the 5v pin on the UNO to a shield board? I have a Sparkfun XBee shield that powers an XBee-PRO 900HP RF Module from the 5v pin on the UNO. It converts the 5v to a regulated 3.3v for the xbee and at maximum transmit power, the xbee pulls 290ma max, 215ma typical. Assume that the power supply to the UNO can provide a minimum of 2 Amps at 7.5 v.
sderodeff:
What is the max current available from the 5v pin on the UNO to a shield board?
It depends.
USB power has a limit of 500mA (a 500mA polyfuse).
An Uno (50mA) would have 450mA 'available', a Mega (70mA) tops at 430mA.
External power could be worse.
An Uno drops to ~100mA when powered with 12volt.
But 7.5volt is still ok.
I calculate 1/(7.5-5)= 400mA if 7.5volt is connected to V-in, assuming 1watt dissipation in the regulator.
And 1/(7.5-0.7-5)= ~550mA if 7.5volt is connected to the DC socket.
Leo..