Final_report___Title_page.pdfFinalReport.pdfFinal_report___optical_pickup-1.pdfAnalysisdetect_small_object_movement_circuit.pdfAng, King, Lam, Lao, Yang EE – 198B May 25, 2006 Final Report Running Head: PHOTOVOLTAIC CELLS Optical Electric Guitar Pickup Department of Electrical Engineering San Jose State UniversityAbstract This report illustrated the designs and specifications of an optical electric guitar pickup. The optical pickup detects signals from the strings and converts the signals into audio signals. The project was divided into three subsystems: detection, amplification, and summation. The detection stage consisted of six optical transmitters and three photodiodes all with the central wavelength of 940nm. The signal was then sent to the amplification stage, where we amplified the signals and adjusted for the DC offset of the signals Finally, the signals were combined at the summing stage before being sent to the quarter jack. This report also included an analysis of why we changed the design from the reflection method to the transmission method.Optical Electric Guitar Pickup by Ang, King, Lam, Lao, and Yang Page 2 Introduction Most musicians pursue quality sounds from their instruments, but the sounds that are produced are always distorted by noise. For an electric guitar, noise may be generated by the surrounding electronics, such as fluorescent lamps or transformers from other electrical and magnetic equipments. To minimize this problem, we came up with the design for an optical pickup for an electric guitar using infrared light sources and detectors. Most optical pickup system employs an enclosed case for the pickup to shield the pickup from the surrounding light sources, since a typical optical pickup uses visible light to detect the vibrations of the string. A typical optical pickup also filters potential undesirable light signals coming from around the stage, thus minimizing the noise that will be produced when it is used on stage. By filtering the signal, the pickup may also eliminate some of the higher order harmonics from the strings, which is an important component of the audio signal. By choosing to use infrared light sources for our project, we will be able to lower the noise generated from the surrounding light sources. In addition, the humming noises that most magnetic pickup produces will be greatly reduced by the optical pickup as we eliminate most of the noise resulting from the surrounding magnetic sources. The design for our optical electric guitar pickup has four specifications. First, the pickup will produce an output signal within the frequency range of 20 Hz to 20kHz, which is the limit of perception of the human hear. The second specification requires the pickup to be able to detect the different frequencies from the strings, including the higher harmonics. The third specification is to have a low noise output and an amplified signal. In other words, the pickup has to produce an undistorted and usable signal. Lastly and the most important specification of all is not to change or modify the techniques of playing a guitar. This optical pickup is consisted of three separate stages. The first stage is to extract the analog signals from the optical signals. The second stage is to amplify the detected signal using variable gain. The amplification stage will amplify the detected signal and adjust for the dc offset resulting from each sensor. The last stage of the project is to combine the signals from the three sensors using a summing amplifier in the non-inverting configuration. Finally, the output of the summing amplifier is fed into the audio amplifier through the quarter-jack. Procedure: In this project, we will try to extract the audio signal from the vibrating strings of an electric guitar by means of optical transmission. In the original design of the project, we proposed to use a reflection method where we place an array of infrared LED into the body of the guitar and point the array in the direction of the strings. Theoretically, the infrared wave will then reflect off the strings and into the sensors that we placed in the body of the guitar. In the original design, we would expect the reflected signals to be amplitude modulated and we would need to place a low pass filter at the output in order to extract the modulated signal. Before we attempted to implement the reflection method, we experimented with the project by using a laser pointer and a photo-resistor. We pointed the laser pointer directly at the photo-resistor andOptical Electric Guitar Pickup by Ang, King, Lam, Lao, and Yang Page 3 place the low E string in between the laser pointer and the photo-resistor. We then connected the leads of the photo-resistor to the oscilloscope to see if we can detect the vibration of the string. With the laser pointer and photo-resistor setup, we were able to see the changes on the oscilloscope as we move the laser pointer around the photo-resistor. We then tried to detect the motion of the string by placing the low E string between the laser pointer and the photo-resistor. We were unable to detect any signal using the oscilloscope as the string vibrated between the laser pointer and the photo-resistor. We then attempted to reflect the infrared signal off of the strings by placing both the infrared LED array and the sensors in the body of the guitar. We varied the incident angles of the LEDs array while attempting the reflection method, but we were once again unable to extract any signal from the reflection of the strings with the different angles that we tried. We were able to observe the background infrared noise due to the fluorescent light to be around 50mV and we were able to eliminate this by covering the entire apparatus with a box. We concluded that if we only use the infrared LED array and the photodiodes, we would not be able to obtain any usable signals due to the lack of reflections and the excess infrared noise that surrounds us. We then attempted to reflect the signals off of more reflective materials, such as aluminum. We tested our hypothesis by reflecting the LED array off of a piece of aluminum foil and place the strings in between the LED array and the aluminum foil. While the sensor was able to detect the general movement from the reflection due to the movements of the LED array, we were still unable to detect any usable signal from the vibration of