I'm trying to get a constant 12VDC signal to turn into what is in the picture.

 

You can't. That is the essential definition of DC. It doesn't change. If it was changing it would be an AC signal.

 

That is not going to be easy.
Why are you trying to do this?

 

A MCU-based solution might be the simplest option. What is the pulse repetition frequency of the waveform?

 

The voltage on pins 2 and 6 is a sawtooth. It is a DC signal with AC components. The input to the circuit is DC, the integrated circuit is an NE555 connected as an astable multivibrator.

 

it can be done with a Schmitt trigger