By the scope auto measurement it shifts but not by a linear proportional amount. In the second trace, I added ~100nF of capacitance in parallel. The effective capacitance is 53% of the measured capacitance. The resonance frequency shifted quite a lot. In the first trace, I have the same L & C but in parallel. I hope this is encouraging to anyone else getting started on LC resonant circuits!ĭidn't work out so well in parallel.
As a first go at it, I felt I wanted the borders to verify correctness. I also should use all 10 horizontal divisions instead of 8. Also I should offset the display to see only the top half of the wave.
HW TO USE MACSPICE TO CALCULATE CURRENT MANUAL
That way it's easy to use the scope auto cursors to find the resonant point instead of all the zooming and manual manipulation I had to do. To do it more thoroughly, I think I should configure it as a parallel circuit, that way the current is minimized and the voltage is maximized at resonance. Ultimately I will build this parallel but the resonance is the same so I just left the series configuration in place to do the "bode plot". That's not possible as a parallel circuit. I did it as a series circuit because prior to this, I was looking at the individual L and C as individual components in the LC circuit, to see their individual contribution to the overall circuit. Next I'll play with series and parallel resistance to see the effect on Q. The Q looks pretty low to me but I don't have a really good intuition about that yet. Maybe if I turn on the FFT channel I'll effectively get that. I wish there were a way to display the vertical scale log instead of linear. I'm amazed how close to theoretical the result is. Read a bunch of web pages, watched w2aew #54 #55 #56 (all 3 re: L and C resonance), watched Dave's #396 (use scope to create bode plot), ran the theoretical numbers and built a circuit on breadboard.
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