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Transcript
Hardware Description Interactive Audio-Controlled Ferrofluid Sculpture Odin Ringsred WWU 5/9/13 Introduction: The interactive ferrofluid sculpture consists of seven different sculpture pieces that can be manipulated with audio and preset patterns. Each sculpture piece is an electromagnet of adjustable strength, which interacts with the magnetic liquid known as ferrofluid. When using audio as an input, each of the seven different sculpture pieces represent a frequency band from 63Hz to 16kHz, which are used as a graphic equalizer to visualize the frequency spectrum of the audio signal by the intensity and shape of the changeable ferrofluid sculpture pieces. Audio inputs include a standard phone jack for a mp3 or CD player, ¼” instrument jack for guitar, and there’s an on-board microphone for capturing the surrounding ambient sound in the room. There will be a keypad and an LCD as a user interface to switch between modes and control the input channels. The preset digital patterns will be selectable via the menu on the LCD, and provide a simply and captivating centerpiece and visualizer. Hardware Overview: The sculpture is made up of mostly analog based circuits for handling all of the signal leveling and adjustment. There are preamps and line leveling circuits for the audio inputs, noiseless audio switches, analog mixer, seven-band graphic equalizer, audio speaker amp, electromagnet driving circuitry, and digital interface ICs such as the DAC and the demultiplexor. I chose mostly analog components to reduce the MCU requirements, and in addition to the circuitry mentioned above, there will be an LCD, pushbutton keypad, and LED indicators show the current status of channels and the like. Power: All of the components in this design, including the MCU, operate off of the ±5V or ±12V rails available from the 380W Antec computer power supply. I chose to use a computer power supply because the electromagnets and the high-power amplifiers draw a significant amount of current and dissipate a considerable amount of energy, which I was sure the Antec Supply was able to handle and provide. It also has an off/on power switch and cooling fan, which also eliminates the need for the additional cost of adding them separately. Switches: For switching in between audio channels I chose to use the MAX4622 (dual SPDT) and MAX4623 (dual DPST) audio switches. They each have internal DC blocking to prevent DC voltage pops when switching and are break-before-make switches. This is an important feature of the switches because small clicks and pops can become a real annoyance when amplified. Using these switches also allows the entire system to be controlled by the MCU and a few I/0 pins. The MAX4623 switches are used to turn on and off the different audio channels including the stereo phone, instrument, and ambient microphone channels and each channels indicator LED. The MAX4622 switches are used to switch between the digital and audio channels (or modes) for driving the electromagnets, and also to bypass the mixer section. One of the two switches on the mixer bypass MAX4622 is also used to as a mute to the speaker. Input Circuits: There are three audio inputs total, two of which are user inputs, and one which is internal to the device. Since the ¼” instrument and stereo phone jacks are used directly by the operator, I have used the impedance bridging concept to avoid impedance matching circuitry for the variable output impedance found in electrical instruments. Zener diodes are used to protect both of the user controlled inputs from accidental high DC voltage inputs that could damage the other circuitry. The stereo phone and instrument inputs have a high pass filter with a cutoff frequency of 1 or 2HZ to block any DC signals from distorting the audio signal, and then go through a unity gain op-amp buffer for impedance matching. After each level is filtered and brought to a level around 100mV, each signal then goes through and amplifier with a variable gain from 1 to 30, to bring the expected signal up to professional line level (4dBu). After the channel levels are adjusted they are combined by a summing amplifier and then have frequencies outside the audible range (20kHz) filtered out by the amplifiers low-pass filter. The output of the summing amplifier has two zener diodes to prevent large audio signals from overdriving the mixer stage. All op-amps used in the audio filtering and leveling are NE5532N dual op-amps with a low noise (CMRR) that makes them ideal for audio applications. Because each eight pin DIP has two op amps, it will save on cost and board space. Mixer Circuit: The mixer (or graphic equalizer) circuit is a made up of seven different narrow-band filters, each with their own frequency band centered at the frequencies 63Hz, 160Hz, 400Hz, 1kHz, 2.5khz, 6.25kHz, and 16kHz. Each of these frequencies corresponds to a different sculpture piece, and with the potentiometers, one may adjust the gain of each band individually. The outputs of each of these filters are then summed up and the signal’s magnitude is attenuated 100 times by the summing amplifier, which also provides a gain of 10 for overall volume control. The attenuation just mentioned is necessary to bring the signal level down to ~100 - 400mv for input into the TDA7297SA audio/speaker amplifier and the MSGEQ7 seven-band graphic equalizer IC used in the electromagnet driving section. There is one MAX4622 dual audio switch that controls the audio signal bypass route, and also the mute function of the audio amplifier. The mixer bypass switch is pretty self-explanatory, and the audio amplifier is wired to have the switch turn on and off the power to the amp causing it to “mute” the speaker and also turn on the mute indicator LED. There is also a bypass mixer LED that is controlled with the remaining part of the MAX4623 audio switch used to control the microphone channel. Electromagnet Driving Circuitry: The driving circuitry for the electromagnets is controlled by either a digital or an analog audio channel, using a MAX4623 audio switch. Both channels use a multiplexed output which is controlled by the STROBE pin of the MCU, acting as the heartbeat of the driving section. The analog audio channel uses the output of the mixer circuit as the input to the sevenband equalizer (MSGEQ7), which then outputs a multiplexed DC value relative to the intensities of the seven frequency bands mentioned previously. Each of the DC values in the multiplexed output are then sampled one at a time by LF398N sample and hold ICs, which then hold that sampled DC value at their output until the next sampling period. The LF398Ns are each enabled one at a time by a SN74F138 3-8 demultiplexor IC, which is itself controlled by the digital electromagnet selection pins of the MCU. The outputs of the LF398Ns are used as inputs to the L272 high power op-amps, amplifying the output current relative to the input voltage. Because the electromagnets are wound in 23 gauge wire, the max amount of current to safely transmit power continuously over time is 729mV. The L272 was chosen because it can sufficiently drive the electromagnets with enough current while also guaranteeing that the windings won’t get too hot, because of its max output current rating of 700mV. Since the electromagnets will be driven with DC voltage, they will be made out of soft iron so that they demagnetize quickly and won’t get hot from the DV voltage. The digital channel uses a DAC0808 digital-to-analog converter that has an output voltage of 0 to Vref (5V) based on the 8-bit parallel digital inputs from the MCU. The DC output is multiplexed at the same rate as the audio channel with the MCU’s STROBE pin, and each DC value is routed to the specific electromagnet the same way as with the audio channel. Microcontroller: The MCU used in this design is the MC9S12DP512, which was chosen for familiarity and developmental ease. The main functions of the MC9S12DP512 are to control the switches and channel routing, provide a digital channel for controlling the sculptures, control the driving circuitry, and provide user interface with the LCD and keypad. The MCU is powered from the 5V rail, and has the reset connected to trigger when the supply voltage drops too far for normal operation. Of the numerous GPIO pins used on the MCU, 11 are used by the LCD, 6 for the user menu pushbuttons, 8 to control the digital-to-analog converter, and 9 more to control switches, enable pins, and the timing of the drive circuitry. Other than this, the MCU only needs a 16MHz crystal and a PLL circuit for clocking the system.