Optical Theremin CDR

Transcription

1 William Cane Wissing James Jones Mackenzie Phelps EE 300w Sec 003 Abstract Optical Theremin CDR For this lab we created an optical theremin. A theremin is an electronic instrument controlled without any physical contact. The theremin consists of two major parts, a circuit containing photodiodes that the user plays the instrument with and a LabVIEW program that translates the photodiode currents to output pitch and volume. The LabVIEW program also implements an auto tuner and distortion. The instrument is able to auto tune to all notes, or to select keys C, F# and G, selectable by the user. The user can also control the distortion levels of the instrument and choose hard or soft clipping distortion via the LabVIEW front panel. Introduction The purpose of lab 2 was to create an optical theremin. A Theremin is an instrument which is played without any physically contact. An Optical Theremin absorbs emitted light waves via photodiodes that will be controlled by hand gestures to produce music. The main steps in implementing an optical Theremin include converting the diode leakage currents to voltages and using LabVIEW code to output a sine wave with some variable frequency and amplitude.this project was a design sequence exercise for the group and the main aim of this project was to understand the concept of teaming and to learn the proper design process to meet the design specifications for any given project. In designing the Optical Theremin, several requirements were fulfilled in order to deliver a proficient, user friendly product. These requirements for the LabVIEW Front Panel View and High Level Design, which the user will use to control the Optical Theremin s settings. Adjustable frequencies to output varying octaves Display of the normalized waveforms for the frequency and amplitude as a function of time Numeric indicators for the light intensities detected by each photodiode Adjustable light intensity levels Our Optical Theremin also includes an Auto Tune switch to allow the user to choose the key that he or she would like play in. Each set of keys is depicted by a specific range of frequencies

2 Rationale The Optical Theremin is made of hardware, consisting of the breadboard/mydaq circuit, and the software, consisting of LabVIEW code. Both the hardware and software involved careful planning to produce an efficient device that satisfied all the requirements. Figure 1 shows a block level diagram of the theremin s design. Figure 1: Block Diagram For the hardware portion of the Optical Theremin, an operational amplifier is used to transform the input photodiode current into an output voltage. The two photodiodes generate a leakage current that depends on the intensity of light in the room. These voltages will be read by the MyDAQ and used in a LabVIEW VI to create a sinusoid that will be output by the MyDAQ. The LabVIEW VI will allow the user to control the output frequency, auto tuning and distortion and to calibrate the instrument. LabVIEW is a good environment to implement this instrument as it is interacts with the MyDAQ to read the circuit voltage and output audio. Implementation The first thing that we designed for the theremin was the control circuit. This circuit uses two OP906 photodiodes to control the instrument. These photodiodes are light intensity controlled current sources. Our circuit uses two transimpedance amplifiers to translate the diode currents to voltages, which can be easily read by the NI MyDAQ. Appendix B shows the circuit schematic made in Multisim. Appendix C shows a picture of the constructed circuit. With the circuit constructed the next step was to create a LabVIEW program that converts the

3 circuit voltages to music. Using the NI MyDAQ these voltages are able to be read by LabVIEW. It is important for the theremin to be calibrated to the environment s light levels before it is played so that it operates at its best. Figure 2 shows the calibration code from LabVIEW. It uses a while loop and event structure to read the front panel s Set Max Light Level and Set Min Light Level buttons. Whenever either button is pressed, the max or min voltage from either diode is read and stored to be used by other parts of the code. Figure 2: LabVIEW Calibration Code With the calibration values acquired, the circuit voltages can then be translated to an output pitch and volume. The code calculates the output frequency by comparing the current Pitch voltage to the max and min voltages from the calibration data. It divides the frequency range by the voltage range to get a frequency per volt, and multiplies that by the current input pitch voltage to generate a frequency. It functions similarly for the volume by treating the min light level as 0% volume and the max as 100% volume. It then passes these calculated frequency and volume values in to a Simulate Sinusoid VI s frequency and amplitude inputs. This VI creates an output sinusoid which is written to the left and right channel audio outputs of the MyDAQ which speakers can be connected to. The DAQ Assistant VI controls reading and writing to the MyDAQ. We found that we needed to match the Number of Samples to Write and Sample Rate for the read and write VIs. After modifying the signal in the distortion section of the code the write VI was unable to automatically read the sample rate, so it had to be set manually. The program also implements an auto tuner and distortion. The code for the auto tuner is in Figure 3. Without auto tuning the thremin is able to produce a sound at any frequency within the user selected range. With auto tuning the output frequency is rounded up or down to the nearest note in a key. The code supports auto tuning to the keys of C, F# and G. The unchanged frequency is passed in to a case structure controlled by a boolean toggle and a key selector combo box. The frequency is then compared to a 1d array of allowable frequency values in that key and rounded to the nearest value using the fractional index, rounding and index array functions. The comparison arrays for the key of C, F# and G are created from the code in Figure 4. This code creates a 12x10 array of all the note frequencies

4 for 10 octaves, then removes rows using the delete subarray block to make arrays for each auto tuner key. It then converts these arrays to 1d arrays so they can be indexed easily. Figure 3: Auto tuner Code Figure 4: Key Array Code The last function of the program is distortion. This part also uses a boolean selector and a combo box to allow the user to choose between hard clipping and soft clipping distortion. Figure 5 shows the distortion section of the LabView code. This code takes in the undistorted waveform output after the auto tuner block. Figure 6 shows how hard and soft clipping modify a waveform. In the hard clipping case it thresholds the signal, setting any signal value that is outside the threshold to the threshold value. In the soft clipping case it extracts the parts of the wave that are outside the threshold and scales them down 10x and adds them to the hard clipped signal. This creates a different sound than hard clipping.

5 Figure 5: Distortion Code Figure 6: Hard and Soft Clipping Appendix E shows the front panel of the LabVIEW VI. It contains many elements for the user to interact with the theremin. Set Min and Max Light buttons to calibrate the instrument Pitch and Volume numeric indicators to see current pitch and volume values Min and Max frequency control knobs to control the range of output frequencies Autotune boolean control and key select combo box Distortion boolean control, type select combo box and threshold control knob Pitch and Volume charts Output waveform display

6 Stop button to stop the VI Value Statement This project gave us an opportunity to experience designing a system from the beginning to the end as a group. Even though an Optical Theremin doesn t directly improve human society, the whole design experience improves programing skills in Lab VIEW and circuitry. This project also involves teamwork, project planning and execution to meet deadlines which we will continue to use for the rest of our lives. Conclusion The original problem was to create an instrument to be played without physical contact. Through a mydaq, a protoboard, and LabView programming, we successfully created an optical theremin. There were both hardware and software portions of the project. The hardware included the circuitry on the protoboard. All of our circuit parts are listed in appendix A. The software portion was more of a challenge consisting of the mydaq and LabVIEW code. Much of the lab was presented in simple tasks, i.e. Implement auto tune. It was then up to us to work together to figure out how to implement the correct code. This lab was designed to be open ended. Each of the required tasks could be completed in a variety of ways. It was up to each team to find the best way that suited their current code. Overall, this lab was a tricky project broken down into smaller pieces to make it manageable. The design gave us a simplified version of the engineering process from brainstorming all the way to a prototype. After successfully completing this project, we are ready to apply our newly acquired skills and move onto our final lab.

7 Appendices Appendix A: Cost of Parts Item Description Part number Price/unit Total Units Total Price Photodiode OP906 $ $1.104 Operational Amplifier TL074CN $ $0.470 Resistor 58K Breadboard BB 2T4D $ $19.99 National Instruments mydaq NA $ $ $ Appendix B: Circuit Schematic

8 Appendix C: Constructed Circuit Appendix D: LabVIEW Program

9 Appendix E: Front Panel