Tuesday mini-extra

posted Nov 21st 2006 4:05am by Will O'Brien
filed under: misc hacks

[Jon] noted that this guy is using his Prius as backup UPS for his house. [It's been around, but's it's worthy.]

If you’re having issues with Eagle for the contest, [weirdguy] suggests this tutorial.

[Lain Sharp] sent in his three blind mice project. This is his version of the 3D mouse. with an AVR to send the data to windows via serial port.

[Michael] added an aux ‘input’ to his car stereo in a unique fashion – he wired it directly to the car speakers and drives them from his iPod. [I'm not recommending this, but it's certainly a different approach.]

Finally, [oliverjenks] sent in this table saw finger jig hack – using some random power transistors, light bulbs and a laptop to drive a stepper motor.

If you haven’t already, check out our Design Challenge contest. I finally got some fedex shipping notifications today, so I should be able to officially announce more prizes very soon.

Comments [10]

10 Responses to Tuesday mini-extra

frodus says:

November 21, 2006 at 4:52 pm

that guy that wired his ipod to his car speakers is a complete moron. The ipod is meant to drive small headphones, or comparable size speakers. Car speakers are DEFINATELY overworking the internal ipod amplifier. He’s gonna wear his ipod out in a few weeks. Pity, the video ipod is pretty nice. to whoever else tries this, you’ve been warned. The ipod isn’t designed to push speakers that big. Just doesn’t have the power.

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Michiel says:

November 21, 2006 at 5:08 pm

glad to see the links posts. bring back monday sipping and hack a day links.

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Andrew Rossignol says:

November 21, 2006 at 5:25 pm

Does that ipod thing even work, he says he gets half the volume of his stereo. that is total crap, like the first poster said, it is meant to drive small speakers. please folks don’t do this as it is completely useless and even if it does, it will destroy your ipod.

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bobby koerper says:

November 21, 2006 at 6:24 pm

Driving any speakers directly from the iPod is certainly not dangerous, however, running the car stereo’s amplifier while the ipod is still connected would be a bad thing.
The car speakers are constructed in the same fasion as headphone drivers are, so they would pose no threat to an ipod driving them. The only danger would be wearing out the ipod battery as the speakers require much more current than headphones do (car audio drivers have a 4ohm impedance, and headphones usually operate at 32 or even higher). Even though it is possible, and power to the speakers is proportional to that of headphones, the listening distance yields very low volumes when the speakers are connected to the ipod at full volume.

If you have an older car with a cassette player, the best method of inputting a line-level signal is through the cassette player’s internal connection to the amplifier. It quite commonly matches up with wiring for line-in jacks. Hopefully i can find a spare cassette player to post a how-to in the near future.

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Royce says:

November 21, 2006 at 6:51 pm

Eagle’s UI, like most pro PCB CAD, is a throw back to PCB CAD software before DOS even existed. I personally have to relearn the package each and every time I pick it up because its so odd that I forget it in a couple of months of non-use. If you want something with a more modern UI that your regular MS Windows click habits will transfer to, then try http://www.diptrace.com/ and http://www.new-wave-concepts.com/ed/wizard.html

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frodus says:

November 21, 2006 at 7:19 pm

Did you read what I said? I didn’t say it wouldn’t work, nor that it was dangerous. I said that its NOT a good idea, and he’s driving the ipod too hard. Car drivers are 4 ohm. Correct? and you say headphones are 32 or higher.

Well, do you know that the AMP inside an ipod is not designed for loudness, but for power. Thats how we measure an amplifiers “power” by measuring its wattage. P=I squared times R.

So with a CONSTANT resistance of 32, and lets say the power output MAX of the ipod is 2 watts, what is the current required to source the 32 ohm speaker? its 25 mA.

with a constant resistance of 4, max power source of the ipod is still 2, we get 70mA.

Thats almost three times the designed for current supplied to the speakers. And yes we’re talking max power, since he said the speakers are turned all the way up.

And not to mention that when using a speaker the amps are designed to take the inductance of the earbuds. The inductance in a car speaker is many times that ammount. Inductance in smaller amplifiers is NOT good.

I agree, the volume will suffer, but I’m also saying, that OVERDRIVING ANY amplifier by causing it to supply more current, is NOT a good thing, and should NOT be attempted. Just get a small amplifier MADE for a larger load, and try that.

It is NOT true that ANY amp will power ANY speaker.
Just try powering a 15 inch sub with the the ipod, not gonna work. Its a 4 ohm speaker too (some are lower)… but its got more inductance… and it requires more power to cause the cone to move in order for anything to be actually audible.

It might work, but its going to wear that amp out. It might not do it when testing, but over a long time, transistors and the other components (caps, resistors, inductors) will indeed wear out.

GO ahead, try it. I dare you to brick an ipod.

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Richard says:

November 22, 2006 at 4:31 pm

Not only that, the amplifiers appear to both be connected to the speakers at the same time, so not only is the guy gonna blow his headdeck up by connecting the front and the rear amps in parallel, he has connected the 4 negative channels from the headdeck in parallel, which will toast the drivers for the negative side, particually if he then powers the ipod from the lighter and shorts the negative side of the headdeck amp to the chassis of the car via the ipod.

This is not a hack, it is just plain stupid.

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frodus says:

November 22, 2006 at 5:22 pm

I never even read that far, i stopped reading when he hooked his ipod to the speakers…

bsaically this guy doesn’t have any idea. He acts like its a few water hoses hooked together… if you attach a few together, the water will flow.

He’s got some major flaws to his “design”

this is not a hack and should be removed, in fear that some 16 year old kid with a new car is gonna try doing the same thing.

most headunits are NOT made to have each amp bridged (which is what it SEEMS he’s trying to do)

translation: this “hack” isn’t even worth reading

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Andrew Rossignol says: