Video Circuit 1: Rainbow Phase Shifter

A project log for NES Zapper Video Synth Theremin

Using a light gun to interact with a video synthesizer and produce sound.

Russell KramerRussell Kramer 02/21/2016 at 04:283 Comments

I wanted a bright colourful video output that responds to the audio. What I came up with was a phase-shift-oscillator. It produces three sin waves each 120° out of phase with each other. This produces a rainbow effect when applied to the R,G,B inputs. The circuit produces vertical rainbow bars because it phase-aligns to the Hsync pulses due to a sympathetic oscillation with the porching circuit. By applying audio I can push the oscillation out of phase and produce responsive patterns.

Vertical rainbow bars when no audio is applied.

Adding a 420Hz sawtooth audio input. The monitor refreshes at 60Hz. 7x60hz = 420Hz so there are 7 waves shown on the monitor.


guidoilieff wrote 09/13/2017 at 06:22 point

Hi, this is awesome! Did you use a tl074 for the phase shifter? Thanks!

  Are you sure? yes | no

Yann Guidon / YGDES wrote 02/25/2016 at 13:01 point

Yay ! ring oscillators ! I'm also playing with them at the moment :-)

Have fun !

  Are you sure? yes | no

K.C. Lee wrote 02/25/2016 at 12:35 point

BTW I learnt the hard way to watch what I connect into the virtual ground node with high impedance in my ultrasonic project.  The coupling caused unwanted coupling and oscillation in my design.

I understand you are trying to make oscillator, so this might not matter to you.

Your *unbuffered* *non-decoupled* virtual ground with 50K dividers has an impedance of 25K.  Those 1uF caps can inject signals (your audio input and the output of the 3 opamp) into the virtual ground.  You can connect the cap to GND instead.  

  Are you sure? yes | no