CD40106 and oscilliscope output

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

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.

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

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.