CD40106 and oscilliscope output

[fuper]

Hey everyone - I've assembled a simple test circuit on a PCB using a cd40106 a 4.6uf cap and a 5k potentiometer.

I've hooked it up to my scope and I don't understand the waveform I am seeing.

If i turn the pot all the way down to a few ohms, the wave looks like a sawtooth. If I turn it all the way to 5k it approaches a square wave. The lower I turn the pot the more the square wave sags and eventually forms a saw tooth wave if I turn it all the way down.

I thought that this kind of oscillator would only produce a square wave output?

Cheers,
Shane

 

[Roff]

The output resistance of a 40106 is not zero. When you turn the pot to zero ohms, the cap loads the output of the Schmitt trigger, causing the sawtooth wave.

 

[fuper]

Thanks Roff!

Are there any calculations you can point me at so I can understand this more? I know a capacitor has resistance depending on the frequency but how this loading creates a sawtooth is unknown to me.

Thanks again!

Happy Halloween

 

[Roff]

If you look at the voltage across the capacitor, it will always be a sawtooth. See . There is a lot of other good stuff here, if you want to learn more about electronics.