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Hello All,

So my question is regarding how I can determine the charge of the square voltage source. For example, I need to build a detector that would detect when the pulse of the square wave is at 50 pico Coulombs, how would that be calculated. How can I determine the charge of the square wave from its voltage.

The square wave is imposed on the 60Hz voltage.

Thanks in advance.

## Best Answer

Charge, Q, coulombs, is current x time.

$$ Q = I \cdot t $$.

For varying current, to measure charge passing through a point you integrate the current with respect to time.

$$ Q = \int I dt $$

Your problem will be extracting this from the 60 Hz but you have given no information on the setup.

To measure the charge going back and forth you need to measure the 40 kHz component of the current. Since it's a square-wave then the charge per half-cycle is given by \$ Q = I_{PEAK} dt = \frac {1}{2}\frac {i_{PEAK}}{40,000} \$.