Light Controlled Noise

My work this past few days has entailed trying to refine the way my pick-ups react to movement. My initial attempts with the motion sensor and the ignition coil provide an auditory cue whenever someone was present, but it was a bit of a Rube Goldberg machine. It required more steps than was necessary to complete the task. Another major failing was that the nature of the noise was exactly the same regardless of the size and speed of what caused the movement.
Addressing these issues I have designed a new setup. It involves an array of photo-transistors attached to an array of Darlington transistors. The photo-transistors are used to trigger the Darlington transistors when they are exposed to light. The Darlington transistors then provide a ground for a DC electric motor- turning it on. The way I am able to differentiate one photo-transistor's input from another is by where in the circuit a ground is applied. The motor is attached to a circuit which is normally open and has a number of resistors (the same amount as the number of photo-transistors minus one) hooked up in series on the ground side of the DC motor. The grounds from each photo/Darlington transistor pairing are applied in different places between these resistors along the circuit. This causes a different amount of resistance to be present between the DC motor and ground depending on which pairing has light, and as such, a different speed is achieved by the motor. This speed difference isn't very obvious visually, but the sound difference from the motor is- especially when the electromagnetic field is picked up by the guitar pickups and amplified.
This development achieved much of what I set out to accomplish, but was still not exactly what i was looking for. The lacking, I felt, was in the way this can be used to respond to movement- especially that of people. When we move around, we don't create light wherever we go- But, we DO create shadows. This caused me to redesign my previous circuit so that when light is received by the photo-transistors power is transferred through to the ground side circuit of the DC motor. This stops the motor when light is present due to the equivalence in voltage on either side of the motor. Once a person moves through the space, they block the light to one or more sensors, causing the transistor pairing to close, and remove the power from the ground side of the DC motor- which in turn allows it to operate. This method requires special attention to dropping of voltages over resistors and the prevention of shorted circuits. The benefits are worth it though as less components are required compared to other solutions. For example, an array of relays could be used to do the same task with a little less hassle, but more cost and unnecessary complexity.