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I will receive soon my first logic analyzer but I'm wondering something:

There's only one ground on the analyzer. What if I want to measure at the same time two circuits with two separate power supplies? Can I just use one ground? Should I bridge the two grounds together? (Should be possible as it's the same voltage and I think the sum of current of the two circuits is lower than the maximum current on the ground of both individually.)

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    \$\begingroup\$ What power supplies are you using? A plug pack connected into mains? Do they have an earth pin in the plug? \$\endgroup\$ Dec 18, 2013 at 4:40
  • \$\begingroup\$ An arduino powered by usb and a Nintendo Gamecube without any earth. Probing the joystick outputs \$\endgroup\$ Dec 18, 2013 at 7:16
  • \$\begingroup\$ It's the same problem with oscilloscopes. \$\endgroup\$
    – Andy aka
    Dec 18, 2013 at 8:06

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You should not attempt to measure signals with different ground references on the same logic analayzer. It might look like it's working and it might actually be working but you can never be certain that it is. Possibly, somewhere down the line there is a common ground, or maybe there are faults in your house wiring and that's not effectively the case. At some point, something weird will happen and you'll curse at your setup until you determine that the issue was the lack of common grounds.

Save yourself that trouble now - don't rely on a flawed test equipment configuration. There must be one ground common to all of the signals you are trying to measure on the same logic analyzer.

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