Electronics > Beginners
Fast square wave with arduino and mosfet
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ManlishPotato:

--- Quote from: fourfathom on September 20, 2019, 07:19:57 pm ---
--- Quote from: ManlishPotato on September 20, 2019, 07:06:51 pm ---Wow I'll have to read through your reply a couple of times to understand it. But really, i'm not looking for efficiency and exactness, i just want to get in the ballpark of the right resonant frequency, to calculate the inductance of the coil.

--- End quote ---

In that case most of what I said is pretty useless.  But you may still want to only lightly couple the FET to the tank circuit, otherwise the drain capacitance will effect the resonant frequency.

--- End quote ---
Ok! What do you mean by "lightly couple the FET"?
ledtester:

--- Quote from: ManlishPotato on September 20, 2019, 07:01:55 pm --- Can't check what the value of the cap was right now, and I don't know the inductance of the coil, that was the start of the project, to observe the resonant frequency, to calculate the inductance.

--- End quote ---

Just excite the tank with a sharp impulse and observe the frequency of the oscillations.

Here's a circuit which will excite a tank at its resonant frequency:



Then just measure the frequency and from knowing the cap value you can get the inductance.

Discussion of how it works:

https://electronics.stackexchange.com/questions/282451/how-is-this-oscillator-circuit-supposed-to-work
MarkF:
I made some annotations on your last circuit and have a few thoughts:

 - I assume you are powering the circuit by +6V through R1.
 - Remove R2 as it is not needed.
 - IF YOU CONTINUE TO CONNECT YOUR SCOPE AS INDICATED, YOU WILL NOT HAVE IT LONG. 
Or you will short out your circuit.  Actually, I don't see how you managed so far unless you are powering the circuit from a battery.



 - You want to connect the scope GND clip to your circuit GND.  Then probe across the MOSFET as shown.

MarkF:
A quick refresher:

   
ManlishPotato:
That's a good pointer, but the power supply and arduino that i'm using are actually mains earth isolated, or floating :)
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