OK an oscilloscope is probably the wrong tool for this job. Consider a battery powered laptop operating on battery power with a resistive attenuator.
Laptop internal audio line inputs run anywhere from 5K to 50K.
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I'd go with a 10:1 attenutaor, high resistance to high, junction of high [tip or ring] resistance to low resistance to sound card hot in, low side of low resistance to neutral and sound card low [sleeve].
I'd place 6 1N400x diodes, 3 in series wired antiparallel. Anode of one string to cathode of the other string to limit the maximum voltage to ~2.1V.
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I like Dale aluminum shell resistors that can be mounted to metal. Ground the metal for safety.
I use 9k from hot to 1K with goes to neutral. I'd place a 10k pot across the 1k and adjust for 1V with a DVM.
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Record with a program like Audacity, a freeware program. I'm not familiar with freeware FFT software but Audadcity does have FFT, I have no idea how good it is.
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"Yes, Audacity does have an FFT (Fast Fourier Transform) display, which is accessible through the "Spectrogram View" feature, allowing you to visually see the frequency components of an audio file over time by utilizing the FFT algorithm to analyze the data;?you can also access a "Plot Spectrum" function to view a single snapshot of the frequency spectrum of a selection within your audio file, also based on FFT calculations.?
Key points about Audacity's FFT display:
¡¤??????????????????????????? Access:
To view the FFT display, go to the track menu and select "Spectrogram".?
¡¤??????????????????????????? Function:
The spectrogram shows how the energy distribution across different frequencies changes over time.?
¡¤??????????????????????????? Plot Spectrum:
To see a single snapshot of the frequency spectrum, go to "Analyze > Plot Spectrum".?
¡¤??????????????????????????? Underlying Calculation:
Both the spectrogram and plot spectrum use the Fast Fourier Transform (FFT) algorithm to analyze the audio data
FFT will display the spectra with harmonics, the time display will show a normal waveform, which, unless there is more then ~10% harmonic distortion, probably won't be visible.
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Now for UPS 'quasi sine wave' outputs, the time display may well show you some really odd waveforms.
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I don't use Audacity, I use Adobe Audition, which has similar capacities but is not freeware. Way not freeware. Obscenely expensive.
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Please remember the dangers remain the same.
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Record the waveform, then disconnect the AC and play with Audacity.
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My rule of thumb is to stay connected to dangerous voltages only as long as necessary.
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We compared an expensive Rigol DSO FFT with a mediocre laptop for audio FFT, the cheap PC blew the Rigol away.
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Part of any measurement process is picking the best tool(s). That can be difficult with all the sales hype for scopes etc.
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I asked about age because at 14 I knew everything and took way too many chances. At 61 you've lived long enough to know your limits. So the age of someone I don't know becomes an issue when trying to offer technical help.
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I added a phone to a girl friend's (not romantic) bedroom. Hid the wiring, removed the bell, life was good, until the phone rang when I had one wire connection in my mouth while completing the other.
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Let's just say the sudden wetness at my crotch was the least of my concerns. 90V at 28Hz flowing through your mouth to your hands is an extremely interesting experience. I was 14 and my thinking was normal for a 14 year old, I didn't think far enough ahead.
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And yes I realize how dangerous that was and how lucky I was to only have wet pants.
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So age is a valid question when dealing with hazardous voltages.
