I have a female USB connector that I want to use to power a little piece of electronics I'm working on.

I have a USB cable plugged into a computer with the socket on the other end and I'm using my multimeter to test the voltage down the cable. When I place the multimeter prongs onto pin 1 (5vDC), and pin 4 (ground), I get a reading of ~5.04v, but as soon as I take the prong off the ground pin, the voltage stops. Does this mean when I solder the socket to my PCB, I need to ground pin4 somewhere to close the circuit?

  • \$\begingroup\$ You have to create a "close circuit". If you don't connect the GND pin you have only a "open circuit". \$\endgroup\$ – Jesus Castane May 30 '13 at 8:16

When you place your multimeter leads on two pins, it creates a circuit that allows your multimeter to measure the voltage. If you don't connect both leads of the multimeter to form a circuit, the multimeter will not measure the voltage, even though the voltage is still present.

If you are using the USB socket for power, then you need to connect the ground of the socket to the ground of your circuit. At a simple level and without knowing more about your circuit, as long as you connect ground of the USB socket to your circuit ground somewhere you should be fine.

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