# simple oscillator formula

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##### New Member
Hello, I am working on a simple oscillator that uses two inverter gates, a resistor and a capacitor. I planned this out a while back, but I cannot find the formula I used to calculate the frequency. I also can't find anything online that resembles the circuit that I am using and also gives a formula for it. Can someone help me out here? I attached the schematic.

Thanks,
Josh Clark

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#### dougy83

##### Well-Known Member
I would assume that the following would be correct:
Code:
F = x/(RC)
Just build the circuit and measure the frequency. Then you can calculate x. Then you can calculate the rough frequency for any RC.

##### New Member
Ok thanks for the suggestion. I was going to use that as a last resort, but I guess it's the only choice now.

I just thought it was weird that I had a formula for the frequency when I first planned it out, but I couldn't find it later so I wanted to check to see if anyone else happened to know it.

#### dougy83

##### Well-Known Member
Actually, before you give up, have a look at
Square wave oscillator (2)

You will note that there is an extra resistor used, Rp, to 'protect' the CMOS input. It also has the added function of preventing the capacitor from being discharged through the CMOS input diodes (this affects the duty cycle & frequency, so the above f=x/r/c is no good due to the diodes affecting the timing)

#### Hero999

##### Banned
Rp is just a high value resistor 100k to 1M is normally good enough.