DIY Active Noise Cancellation

[phrontist]

Ah Ha! So it's possible! The question now is whether a highschool student with fair knowledge of electronic theory and mediocre soldering skills can do it. I'd really like to have these for our driver next year, seeing as to how it could be me

[Max Lobovsky]

Originally Posted by Phrontist

I'd really like to have these for our driver next year, seeing as to how it could be me

That would be pretty cool if you could DIY, but isn't there a rule about the operating team using things to assist them. I'm not sure if this qualifies..

[Adam Y.]

That would be pretty cool if you could DIY, but isn't there a rule about the operating team using things to assist them. I'm not sure if this qualifies..

Nah. I doubt this is related to FIRST. Besides you wouldn't be able to hear the coach yell,"DEFENSE. DEFENSE. DEFENSE."

[phrontist]

The arguement can certainly be made that the driver is an extension of the control system, and the headphones an extension of him or her. I don't think we'd run into problems.

[RogerR]

Originally Posted by phrontist

The arguement can certainly be made that the driver is an extension of the control system, and the headphones an extension of him or her. I don't think we'd run into problems.

err..actually, i think that they might not let you. i recall someone asking FIRST via the Q&A forum if the human player could listen to music to help him keep his "rhythm". FIRST didn't allow him to use them based on G10. while that rule applies to human players, i wouldn't be suprised if drivers were held to a similar standard.

[henryBsick]

Originally Posted by RogerR

err..actually, i think that they might not let you. i recall someone asking FIRST via the Q&A forum if the human player could listen to music to help him keep his "rhythm". FIRST didn't allow him to use them based on G10. while that rule applies to human players, i wouldn't be suprised if drivers were held to a similar standard.

@ nats I listened to music on headphones right up until the start of the matches, then put the headphones around my neck. No one seemed to care. With active noise cancellation, or disruption, or w/e it is called, I don't think it will be a problem.

-Henry

[Elgin Clock]

I actually just saw something today at a beauty supply shop that I thought would be perfect for our drivers (who were with me at the store) to use at FIRST events. Basically what it was, was a single earbud that you wear on your ear, but it had a timer and an audible signal built into them. They claimed to be able to time from 1-90 minutes, and I thought they would be perfect for our drivers to wear, maybe set them for about 1:30 and that would be like an audible warning to the drivers to step it up a notch and make your last ditch attempts for the bar, or for the balls or whatever you had to do for your strategy.

Sorry for posting this in your thread, but it does kind of relate to your idea, and I just wanted some feedback from you all as to what you think of this idea.


(And don't ask me what I was doing in a beauty supply store with some of my teamates, unless you really want to know what we were up to... lol )

[JohnBoucher]

For what it’s worth.. I believe 237’s drive team just ignored everything except the drive team members on the playing field.
Elgin…. How about a buzzer device embedded in the control box so the drive team would feel it at a predetermined interval?
Also did you have the team in for a pre Beantown Blitz bikini wax???

[Al Skierkiewicz]

phrontist,
Yes it is possible for you to build noise cancelling headphones. What makes them expensive is all of the auto adaptive circuitry reguired for varying acoustic conditions. Effectively what you need to do is sample the noise, phase shift it so it arrives at your ear 180 degrees out of phase with the noise and at the same level and there you are. The auto circuitry samples the environment, determines what is noise and only amplifies/shifts that part of the spectrum with a little AGC thrown in for level adjusting. With DSP on the rise, it is really easy to get a good sample, analyze what is audio and correct for the rest. If you have a good idea of what the spectrum of noise is, then you can build a simple filter to just pass the noise to the phase shifter and amp. Throw in a tuning control and level control (knobs on the box) and you don't need to add the auto circuitry. Just tune out the noise as best you can.
So here is what you need...Mic preamp, tuneable filter, phase shifter, power amp. You should be able to put it together with parts from Digikey into a case that fits into your pocket. LM324 opamps should do nicely for the everything but the power amp. LM386 for power amps (you need two for stereo phones.) Have fun! There is a simple book "Op Amp Cookbook" that ought to be a big help.

[Andrew]

There used to be a big "hobbyist" electronics movement in this country. I have watched this steadily decline over the past several years. You may be able to find a hobbyist area on the internet and get plugged in.

There were two magazines (Popular Electronics & Electronics Something) which merged into Electronics Now about four years ago. These magazines published circuits especially for audio applications. If you can dig back into that archive, you'll find some audio circuits to do the various tasks that Al mentioned.

You need to start with a condensor microphone element (available from Radio Hut or from Digikey). A condensor mic takes sound waves and converts them into a change in capacitance. You need a preamplifier circuit to take this change in capacitance and convert it into a voltage. Good luck on finding such a circuit. There were many in the Popular Electronics. Since Pop Elec is referenced in Applied Science and Technology database, you can probably do a real lit search and find one.

You might be able to find a data sheet for the condensor microphone which gives you a circuit to preamplify it.

The output side is the driver is best done with an LM386. I'm pretty sure this chip is not obsolete. If you want to find the circuit to do this, look up the Data Sheet and Application Note for the LM386 on National Semiconductor's web site (if they haven't spun off this part of there business to another chip maker).

You can find the "in between" stuff by looking up the patent for the noise cancelling ear phones. Somewhere out there is a patent search database (on the .gov net). You can acquire patents from any public library. If they don't have them, they can get them through interlibrary loan.

In terms of getting everything working, if you don't have an oscilloscope, I would abandon ship right now.

The LM386 part of the puzzle is the easiest to get working. You can get the parts and wire it up in a couple of weeks. To test, you can take the output of any CD device (CDROM drive for instance) and connect that as your circuit input. Connect the output of your audio driver to a speaker. If you get sound (and the LM386 doesn't heat up and start a fire), then you're good to go. Otherwise, check your solder joints and connections!

[Adam Y.]

There used to be a big "hobbyist" electronics movement in this country. I have watched this steadily decline over the past several years. You may be able to find a hobbyist area on the internet and get plugged in.

Heheh. I caught the tail end of the electronics movement. I managed to get two of Forrest M. Simm's books from Radio Shack before the company discontinued them. I didn't understand them until I bought more electronics books. Im not too worried though. Servo and Nuts and Volts are still running strong and there are now new hobbies that Im reading about. In fact you might want to try out their message board at www.nutsvolts.com They range from Space Exploration to Robotics. I have to dig through my magazines but I remeber there was a headphones set that could cancel out noise for only twenty dollars.

[Al Skierkiewicz]

Originally Posted by Andrew

You need to start with a condensor microphone element (available from Radio Hut or from Digikey). A condensor mic takes sound waves and converts them into a change in capacitance.

You might be able to find a data sheet for the condensor microphone which gives you a circuit to preamplify it.

Andrew,
Not exactly...True condensor mics have built in circuitry that make the conversion from capacitance to voltage internally and they are very expensive ($2000-5000). Most mic elements that you find (cheap at Digikey $2-$4) will be electret condensor mics. These elements have a permanent electrostatic field and as the plates of the condensor (capacitor) vibrate with sound the element outputs a real tiny voltage. This voltage is at a very high impedance so there is an amplifier to lower the impedance and add some gain built right into the mic. For this reason it is necessary to add a little DC power to the mic. Electret spec sheets will have typical power supply wiring, but it is usually very simple, a resistor to power supply is usually all it takes. Follow up with a coupling capacitor to a preamp and you are all set. LM324 are quad op amps optimized for single ended power. You still have to add bias wiring but they are cheap and available and have reasonable gain and distortion.

[phrontist]

Excellent advice Mr.Skierkiewicz! I've been reading a bit about op-amp theory and this looks like an excellent project. Don't have an o-scope, but my physics theacher has a really nice one. Surely this will fill those otherwise wasted summer hours

[DanArgent]

Phrontist is just jealous of my new senn's. Although, the grados that he has are decent. I think this is a great project phrontist and I would love to hel pyou out in the shop. I could see D "the Team" geting into it too once we get the gear box out of the way.

On a side note, are you sure, that Condensers are $2000+ I work with a few sure condensers that I think were more in the range of $1000.

[Al Skierkiewicz]

Originally Posted by DanArgent

On a side note, are you sure, that Condensers are $2000+ I work with a few sure condensers that I think were more in the range of $1000.

Dan,
The Shure's are electret, are you using the SM81? That is an electret. True, non electret condensors will be from manufacturers like AKG, Sennheiser, and of course the Neuman U67 tube mic. Many of them will be in large cases to hold the electronics needed to convert the condensor output to a useable signal. Many mics are coming out that look like classic mics with big cases and heads that are electrets made to look like a classic. Remember that each mic has it's own distinctive sound and good audio people can tell a mic (model) by listening to it.