I attached split the end of a USB wire and attached a switch. When I press the switch, I measure 5V from the port, but am only measuring 33mA. Why am I getting only 33mA instead of 100mA?

  • 1
    \$\begingroup\$ What is the other end of the USB cable plugged into? \$\endgroup\$
    – pingswept
    Oct 30, 2010 at 6:34
  • \$\begingroup\$ It's connected to the multimeter. \$\endgroup\$ Oct 30, 2010 at 16:32

1 Answer 1


There is a decent chance that the computer is detecting a short and limiting the current back.

As pingswept said,

try a 50 ohm resistor

This will stop the computer from thinking there is broken hardware connected.

  • 4
    \$\begingroup\$ I think Kortuk is on the right track. Try putting a 5 V / 0.1 A = 50 ohm resistor in series with the switch. \$\endgroup\$
    – pingswept
    Oct 30, 2010 at 6:36

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