1. Problem Description: Design and build a guitar pickup using optical methods, as opposed to traditional magnetic or piezo-electric pickups. Objectives: Must not modify the guitar or impede natural playing. Whole system should be removable. Have the ability to process the signal using either analog or digital means. Must be able to handle environmental noise. Power for the unit must last at least a couple songs. Special Thanks to Dr. Dorin Patru (Tech. Advisor, Customer) Mr. Les Moore (Guide) Professor Mark Indovina (Tech. Advisor) Dr. Carlos Barrios (Tech. Advisor) Dr. Ivan Puchades (Tech. Advisor) Mr. Ken Snyder (Guitar Expert, Purchasing) EME Department Mechanical: Individual sensor mounts for each emitter-detector pair to allow many points of adjustment. Allows for emitter and detector offset from the string to change the amount of light received. Whole sensor mount slides on a guide to zero the string in the sensor’s line of sight. Processing: The signals obtained by each of the six sensor channels are sent through a gain amplifier to allow for proper voltage ranges required by the microprocessor. After the gain stage, the signals are processed using either analog or digital means, depending on the status of the Analog/Digital switch. System Overview: Results: Each component of the system was tested individually with a high rate of success. Both the analog and digital processing paths have been successful in recreating the original signal and outputting the result to an amplifier for auditory confirmation. Every objective presented by the customer was met. Overall, this project proved the functionality of an optically-driven guitar pickup. From left to right: Rachel Arquette (EE), Chris Perry (EE), Joe Mauger (EE), R. Paul Hoops (EE), Chris Steele (ME), Ye Kuang (EE), Caroline Lichtenberger (EE) Sensors: Each string has an emitter-detector pair consisting of an infrared LED phototransistor. Signals are generated by the string oscillations creating variations in the amount of light detected by the phototransistor. Analog: After the gain stage, the signal from each channel will go through a second-order Butterworth high-pass and low-pass filter set to minimize frequency components due to noise sources, such as the 60 Hz noise from electrical outlets, and allow the first two harmonics of each note to pass through un-attenuated. Once filtered, the six channels are then summed into one signal using a summing amplifier and sent to the ¼” jack as the output. This processing path uses two matching PCBs, as shown. Each PCB contains the hardware for three string channels. Digital: The processor uses 6 ADC channels to read each of the signals from the gain stage. These signals are then sent through digital band-pass filters, summed together, and sent to an external DAC via SPI. Application-specific guide bed allows for reliable re- installation of the unit. Guide is strapped to guitar with soft nylon web strap for easy installation and removal. Sensors (x6) Analog Processing Digital Processing Output to Amplifier Phototransistor Infrared LED Guitar String Analog Processing Hardware Digital Processing Flowchart Microprocessor Evaluation Board P13323: Opto-Electric Guitar Pickup Analog/Digital Input Switch Analog/Digital Output Switch Digital: Test Signal Output of DAC Analog: Guitar Output of Summing Amplifier