It should be 0V to peak.
Why it used 0V to 15V, can it be change?
The original voltage and waveform.

Hey that's great, thanks for your work! I will need to study it to see if I understand the changes.

Yes you are right, it's 0V to peak. My power supply secondary is +/-18V RMS so ~26V rectified. I put an L7815 and an L7915 on it to power an active filter that uses NE5532s. NE5532 has a maximum supply voltage rating of +/-22V and a recommended +/-15V. So this is the reason for the 15V. I could add something for 6V if it's a big advantage but I would rather not if 15V is ok.

What do you think about the phase shift? My current guess is the voltage needs to change for there to be phase shift so with a square wave there will only be phase shift on the rising and falling edges. Is that correct? In the attached photo there is of course 180 degrees shift because of the probe GND relative to the test points.

And I guess my second question from post #19 was already answered by ronv as you do not want to short out your supply.

EDIT: Oh by the way, I actually bought some IRF540s but my LTSpice version only has IRF530. In case it makes a difference.

 

I will choose the Vin = 9V, because in most situations, it will not damage the input of G, S, and if you use the Vin = 15V, when R1 is shorted then Vgs will be more than 22V, so it could be damage the input of G, S.

When LM555N running over 100Khz then the pulse could be shaking, if you do not care about that then it's ok.

I'm not sure what you expect for the output, because the phase shift already made when you used that kind of circuit, if you want to improve the signal that I drew circle with pink then you could try to reducing the values of R3, I think that is the R3 resistor a little higher to limits the current flows through to the coil, so the voltage of coil can't raising up quickly.

 

A square wave can be modify to a sine wave, I have tried two methods, the one was used the RC integrators(filters) and another one was used the LC filter, the RC filters will decreasing the voltage amplitude and the LC filter will increasing the voltage amplitude.

 

I was looking for phase shift to see if my inductor was working. If I simulate it with a high frequency sine wave I get almost 90 degrees phase shift. If I simulate it with a square wave I get various weird stuff. Attached is an artist impression of the square wave phase shift I was sort of expecting.

But I realize now that a square wave consists of many frequencies and each frequency will respond differently to the inductor.

 

The square wave can be using the counter to divide the input clock when it match the period of time you want.

Another method to approaching the 180 degree phrase shift is to use RC filter and schmitt trigger IC as MC14584 or CD40106, using RC filter to do the delay time and using schmitt trigger IC to do the wave form modify, and also using the transistor or CD4049 to raising the voltage to Vcc of IC.