This week the group worked on updating all proposal documentation including proposed budget, power budget, engineering specs, previous progress log entries, and references.
The proposed budget was updated to include more specific components, quantity, and pricing details. Cost of lab equipment used in the last weeks was also added with “Valencia Property” denoting use of college-owned equipment.
John
In order to conduct more Proof of Concept testing, the team requires a plane-wave tube. The test bed will allow for attenuation measurements to be conducted using a loudspeaker as the noise source.
This test bed can be later modified to suit the requirements of ANC system testing/calibration.
John began constructing the test bed this week. In order to generate plane-waves down to at least 50hz, the tube must be at least:
L = 1130/(4*50) = 5.65 Ft. [3]
The 8” diameter tube comes in 4’ sections so two sections will be placed end to end giving a final length of ~8’ and a Low Frequency limit of ~32Hz. Careful attention is needed to ensure no air gaps at any point along the tube
The highest frequency measurable is dependent on the tube diameter such that:
(1.22*1130)/(8/12) = 2067.9 Hz [3]
It should be completed in time for testing on either Sunday 11/7 or Tuesday 11/9.
John also sent an email to Joseph McBride, Lab Manager for Sound and Music, on behalf of the group.
The email outlined the project goals and testing needs as well as requesting a semi-permanent installation of the team’s test bed in one of the departments recording spaces.
While calculating filter component values last week, John thought it would be useful to have an Octave program that would automatically run the formulas for given inputs.
During the weekend, John wrote up a program capable of computing resistor values for active filters up to 10th order.
The program can do this for both HPF and LPF with either Bessel or Butterworth responses.
Solutions found according to [4] and [5].
Hunter
The majority of this week has been tasked with completing all the proposal documents mentioned in the opening statement, Hunter’s Pspice education license was deactivated recently and approval is required for another year. After weeks of waiting, it was approved yesterday.
This software has already proved beneficial to our design, especially now that Pspice for Texas Instruments (Ti) has been added to Pspice. Ti’s component kit for Pspice has a good majority of Ti components, although not all, but most. Some of which, we will be using in our design.
The following documents are what the team accomplished throughout the week.
Group
The team added some images for each module in the engineering specs document as a visualization aid.
Further work was also done to provide greater clarity and specificity to the requirements of each module regarding its contribution to the project.
Some modules were assigned for individual focus while others will be developed by the team equally.
John created an official power budget in Excel and filled it with supply voltage/current specs from the data-sheets of each relevant component. These data were then used to compute the estimated power consumption of the entire system.
The Data-Sheet of the LM1875 Power Amplifier provided plots of the relationship between supply voltage/current, power dissipation, and output power. These were used to estimate power consumption with a ±18V supply.
In order to determine the current requirements of the power supply, current values for each voltage rail (3.3, +5, -5, etc.) were added together.
All currents for the ADAU1466 were added to the 5V supply. The evaluation board is powered by a single 5v supply.
Unfortunately the 3rd party board manufacturer does not supply detailed documentation.
References
[1] Texas Instruments, “LM1875 20W Audio Power Amplifier,” LM1875 datasheet, May 2004 [Revised May 2004].
[2] Analog Devices, “SigmaDSP Digital Audio Processor,” ADAU1462/ADAU1466 datasheet, 2017-2018
[3] Audio Engineering Society, Plan-Wave Tubes: Design and Practice, AES Information Document, 1991 [Revised 2003]
[4] B. Carter and R. Mancini, Op amps for everyone, 5th ed. Oxford, UK: Elsevier/Newnes, 2018.
[5] J. Karki, “Analysis of the Sallen-Key Architecture,” Texas Instruments, Dallas. TX, SLOA024B, July 1999 [Revised September 2002].
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