Squarewave VCO Modulated By Triangle LFO

I designed and built a squarewave oscillator with a triangle LFO that modulates the squarewave to make a vibrato effect. The oscillation is done by a CD40106BE Hex Inverter Smitt Trigger . At the input of the Smitt Trigger appears a triangle wave and at the output a squarewave. I used two Smitt Triggers where one of them uses the triangle waveform to modulate the input of the other Smitt Trigger which creates the squarewave you hear. The left pot changes the pitch of the squarewave, the middle changes the amount of modulation by the LFO and the most right pot changes the rate in which the LFO oscillates. Schematic as seen in the video: Thanks to casperelectronics synthesizers for the knowledge: