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I have an LM324 in my circuit and I connected the V+ pin to 5V, but left GND pin unconnected (floating), so what value will I see on the GND pin?

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    \$\begingroup\$ Possibly Vcc, but probably depends on what voltages are applied to the other pins. \$\endgroup\$ – Peter Bennett Aug 14 '15 at 23:12
  • \$\begingroup\$ Did you try it? \$\endgroup\$ – Roger Rowland Aug 15 '15 at 4:30
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Using a 10M input resistance multimeter, and referring to the datasheet, the schematic:-

enter image description here

Looks like there's maybe a couple junctions with some resistive stuff between Vcc and GND.

So if none of the other pins are connected to anything, the GND voltage would probably read around 4.5VDC. If there were low (in relation to 10M) resistance paths to ground from any of the other pins, then I would expect a voltage of about 0.7V (because of the isolation junctions to the grounded substrate). It will be somewhere in that (approximate) range, for sure, assuming nothing else is powered.

A more precise answer might be the approximate range of +4.5 to Vx+0.7, where Vx is the lowest voltage that appears on any other pin. It could be higher than 4.5 if the DMM was very high input resistance.

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If something is floating, the voltage will depend on the depend on the impedance of the voltmeter and resistance of that something. The answer - the voltage undefined. From 100kV and more (static electricity on the device's pin) down to 0v.

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    \$\begingroup\$ I think we can rule out 100kV. \$\endgroup\$ – mkeith Aug 15 '15 at 3:01

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