RockSat-C 2012

ISTR

Individual Subsystem Testing Report

Minnesota Sound WreckersUniversity of Minnesota

2/13/12

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Alexander RichmanJacob SchultzJustine Topel Will Thorson

RockSat-C 2012

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Mission Overview

• Our mission is to design and build an Active Noise Cancellation (ANC) system capable of attenuating the noise on board a rocket.– We require at least some reduction in

intensity of noise in the test chamber compared to the control chamber as well as the safe operation of the entire payload.

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RockSat-C 2012

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Mission Overview cont.

• We expect to show that this technique is a viable solution to noise sensitive testing onboard rockets.

• This would benefit any sound sensitive experiment onboard a rocket including any testing in which live subjects are used and it is desired to lower their stress levels.

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RockSat-C 2012

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Functional Block Diagrams

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ANC

speaker microphone

Data Logger

microphone

Power Supply

Wallops activation signal

RockSat-C 2012

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ANC system

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Dummy Chamber

Control Systems

PowerSupply

MicPreamps

Power amplifier

Mic

Mic

Speaker

Speaker

Data Logger

ANC

In

Out

RockSat-C 2012

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Changes from CDR

• Instead of trying to design a complicated ANC system from scratch using a DSP and programming our own control models into it we will be adapting an already built ANC system.– The ANC system found in high quality

headphones work well in the spectrum we hope attenuate sound.

– Some work will be required to integrate the system and optimize its output for our application.

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RockSat-C 2012

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Program Management and Team Updates

• We are continuing with the same overall team organization as last semester.

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RockSat-C 2012

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Schedule Update

• We are mostly on schedule at this time• There has been a slight delay in the

fabrication of the structure.– The shop is backed up with several

projects at the moment but should be able to finish ours in time for testing.

• The ANC system requires adjustments in order to operate correctly and some further testing

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RockSat-C 2012

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Subsystem Overview

• Subsystems involved in our experiment– Active Noise Cancellation system

(Presented by Alex Richman)– Power supply (Presented by Will

Thorson)– Data Logger (Presented by Will Thorson)

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RockSat-C 2012

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Power Supply Subsystem Overview

• We will be using the power supply that was flown last year. We have not conducted extensive testing of this system as of yet.

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RockSat-C 2012

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Data Logger Subsystem Overview

• We will be using the data logger that was flown last year. We have not conducted extensive testing of this system as of yet either.

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RockSat-C 2012

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ANC Subsystem Overview

• We have completed basic audio cancellation testing in our test chamber with our ANC system we recovered from a pair of noise cancelling headphones.

• As of now, our system is not performing as we hoped, but we are optimistic that we can solve our problems.

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RockSat-C 2012

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ANC Subsystem Update - Pictures

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Test chamber with microphone

Egg carton with foam added to top of chamber

Dismantled ANC system from headphones

RockSat-C 2012

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ANC Subsystem Update - Pictures

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Above – Recording audio data in Ableton Live

Below – Analyzing data in Matlab

RockSat-C 2012

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ANC Subsystem Update

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Above – Audio Amplifier to give more power to our speaker

Above – Boundary Microphone to be used with launch

RockSat-C 2012

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ANC Subsystem Update

Testing Procedure•To perform basic audio cancellation tests, we agitated our test chamber with a 300Hz signal, as our ANC system from the headphones has two settings to cancel noise – 300Hz and 120Hz.•We recorded audio data from our test microphone in the chamber with the noise cancellation system OFF, ON(300Hz), and ON(120Hz).

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RockSat-C 2012

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ANC Subsystem Update

Test RMS of Signal

Control Signal 0.0102

300Hz Targeted ANC 0.0439

120Hz Targeted ANC 0.0268

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• Current data shows that our noise cancelling system is not attenuating our noise, but amplifying it. We believe this is may be caused by constructive interference due to the increased distance from the driving speaker to the microphone, as compared to the human ear and the headphone speaker.

• It is encouraging that we get more interference at the 300Hz ANC setting, as it may suggest that we will get attenuation if we can eliminate the phase difference.

RockSat-C 2012

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ANC Subsystem Update – FFT Plot

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RockSat-C 2012

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ANC Subsystem Update – FFT (Wider Range)

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RockSat-C 2012

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ANC subsystem II

• We are no longer exploring the method of building our own ANC system using a DSP at this time– The required components put a severe

strain on space allotted for electronics onboard

– Coding and testing would have taken many hours of work which can better be spent integrating the ANC headphone system into our designs.

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RockSat-C 2012

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Plan for Subsystem Integration

• We have removed the power supply system from the old canister and are preparing to integrate it with our current ANC setup

• Our next challenge is to integrate our subsystems and fit them within the physical constraints of the NASA cylinder.

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RockSat-C 2012

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Lessons Learned

• Noise cancellation is a delicate process and careful control of gains and phases is required to tread the thin line between noise cancellation and noise amplification.

• The direction of this project hasn’t always been clear. Now that we have a clear path, the concern is alleviated.

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RockSat-C 2012

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Lessons Learned

• Our testing methods are working and giving us clear results. The noise cancelling headphone system seems to work.

• We are still working on filtering audio measurements to the specified bandwidth, which will be a helpful step forward to measuring signal power for the frequency range of concern.

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RockSat-C 2012

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Conclusions

• We are no longer exploring multiple ANC systems at the same time.

• We have to try to eliminate the phase difference in order to get attenuation.

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