This simple modification adds a photocell resistor to control our VCF. By using a photocell we are able to have functional control over the filter cutoff frequency by simply moving our hand closer or farther away.
1 x 10kΩ Photocell
1 x Breadboard
This modification only uses one actual component, making it one of the simpler ones we feature on the website. However, we decided to include it because of how fun and dynamic the photocell can be. First we will take +5V from our Arduino at TP18/TP19. We then pass this through either leg of our photocell since it is not a polarized component. We then simply run a jumper from the opposite leg of our photocell into the VCF IN. If we trim our VCF CUTOFF counter clockwise we should be able to hear the change varying light has on the photocell. Where we set our CUTOFF frequency is the maximum change in our VCF using the photocell. For a detailed look at the jumper cable configurations see figure 1.
Figure 1. VCF Photocell mod.
In fact, this modification can be made even simpler if we were to use the EG mode on our VCA. We could simply patch our photocell between the EG OUT and the VCF IN. This will send 5v+ from our EG and apply the appropriate resistance based on how much light is hitting the photocell at that time. Figure 2 shows a visual representation of this simple mod.
Figure 2. EG OUT to VCF IN through 10kΩ photocell.
Fritzing is an open source visual breadboarding software.