My ultimate goal is to generate a sine wave of 25Hz @ around 80VAC. The masterplan is to use either some uProcessor or 555/oscilator circuit to generate a square wave of 25Hz at 50% dutycycle, put a couple of low pass filters behind it to make the squarewave more sine~ish and than amplify the sine with an opamp and lastly I want to use to wind a transformer based upon a toroid to get my designed voltage.
(it is to ring an old phone)
But for now I just want to play around with the simulation. I am gonna need more simulations in the future.
Question 1:
V1 is supposed to output a 25Hz square wave. I don’t fully understand it’s settings. I put the period at 40ms (=1/25) and the pulse width at half. Is this correct?
The V2 voltage source looks correct to me. I want the opamp to be supplied with 12V
The opamp is still configured correctly (I think, I haven’t changed)
My 2nd question, how does the simulator work? I mean what on earth do I have to input here?
When you run the simulation - if you place a probe at the output of VPulse, do you see the desired 25Hz shape? Then add probe after each of the resistors in that filter front end? What’s happening.
When you run it, you can see the output?
See youtube
skip to about 9 or 10 minutes into the video… its running ngspice on an RC network like your front end.
Great, something to consider - if you are going to try generating a ring signal, you might not want to convert to a sine wave in the early part of the process. It’s far harder to create a linear amplifier for 25Hz at the 80V, than if you’d run a used some kind of a power MOSFet, drive a transformer AND then filter out the harmonics.
E.g. Use that square wave to drive the MOSFET, into transformer and then filter. You’d need to match the expected load impedance of the phone – something like 600ohms(?).
So you might want to create a circuit designed using a normal power transformer (6Vac/ 12Vac / 24Vac ) and use the high voltage (120/240) volt side as the ringer driver, plan your network behind it. It should be an easier design. Keep in mind that 80Vac can be lethal !!!. Easy test on the output to see if the secondary is working correctly is to add NE-2 bulb and resistor. There are also symbols for those in the KiCad libraries and ngspice can simulate them as well…
Actually during my ‘queste’ I found an even simpler approach. The most simplistic I found, is to use an H bridge at 12V or so. You PWM both IN channels to generate a square AC output of 12V @25Hz, if you put this output in a transformer and crank the voltage up to 70~80V than then phone should ring perfectly fine.
It may not be a sine, but ofcourse the sine isn’t the goal. A working phone is.
