LM324 generate step wave
SW1 is the on-off switch for both the triangle generator and the bottom circuit.  It is debounced with a 5ms time constant and then fed into the inputs of the 4066 switches.  Unit C of the 4066 switches the op-amp output for either 0V or 6V.  It is smoothed with a 24us time constant, a lot faster than your x-axis.
The y-axis of your measurement is not specified.  What is the range of the spike, which may occur due to the LM324 being a fairly slow op-amp?   It is likely rather small.  Using faster op-amps will bring down its duration and height even more.