Hackaday Links July 18, 2012

Apollo 13 DJ controller Follow Up

apollo13 DJ controller

[Adam] had a really impressive DJ controller build featured here recently. Many of you had more questions about the internals and such, so this post should clarify a few things. He’s still got a few more updates to make, but promises to reveal all if given enough time!

Noise Absorbing Headphones from Shooting Earmuffs


If the circuitry on your microphone-enabled shooting earmuffs has gone bad, the actual speakers may still be good. Why not convert them into some noise-blocking headphones? For that matter, if you’ve broken a pivot, there’s a simple solution for that too!

Help Choosing your CNC Router


If you’re in the market for a CNC router, but aren’t sure where to start, Ponoko has put together a handy pricing guide to several of the more popular DIY routers available.



It’s very hot out, so what is one to do when your shop or garage is burning up?  Why not build your own “AC unit?” Sure you have to supply your own ice, but at under $20 for this cooler-based unit, maybe it’s worth it. Here’s the Reddit thread explaining it as well as a picture of the finished product.

3D Topo Map on a CNC Router


Once you’ve purchased your CNC router using the above guide, why not make your own 3D top map? This tutorial features a map of Ross Island off of Antarctica. Why Ross Island? It was the first vector-format topo map found off of Wikimedia.

[Aaron] shows us what life would be like if [Bob Vila] started hacking headphones


[Aaron Horeth] had a pair of headphones that had seen better days, and before he tossed them out, he realized that he could use them to build a set of custom cans. He had always wanted a pair of headphones with a detachable cord to prevent damage when tripped over, and thought that his old set would be the perfect donor.

He swung by his local hardware store to peruse their collection of construction earmuffs, eventually finding a set that looked decent and didn’t cost an arm and a leg. Using construction earmuffs as the framework for his headphones gave him the durability he was looking for with the added bonus of being designed to deaden extraneous noise. Once he got them home he pulled the drivers from his old set of headphones installing them into the earmuffs, but not before he wired them up to support a breakaway input cable.

There’s no doubt that the modifications are simple, but we imagine they come in pretty handy when tinkering around the shop.

Improving headphones by voiding warranties

[Dan] had been wanting a pair of Bluetooth headphones for quite a while. Most of the reviews for wireless headphones in the $50-$80 range complained of tinny sound and dropped bass. Nevertheless, he stumbled upon a $20 pair of headphones with similar reviews and realized that he could switch out the driver and make a decent pair of cans.

The donor drivers came from a pair of Sennheiser HD 540 headphones. These are very respectable headphone speakers that cost about what you would expect for pro audio gear. To to get Bluetooth working with the Sennheisers, [Dan] removed the PCB and battery enclosure and attached them to the headband with velcro.

For his build, he had to cut the cable on the Sennheisers and solder them to the Bluetooth board. There was never any danger of ruining a good pair of headphones, though. If he screwed up he was only out a headphone cable. Now [Dan] has a nice pair of Bluetooth headphones that can reproduce bass. Not a bad deal for a $20 pair of headphones.

Muff-Fones sound dirty; well, not literally

Baby, it’s cold outside. But that doesn’t stop [Grissini] from listening to some tunes when not indoors. He added headphones to a pair of ear warmers. We guess you could call them ear muffs, which is where the name comes from. But these are the newer type that wrap around the back of your head.

[Grissini] picked up a set of headphones that similarly wrap around the back of your head. After pulling the speakers out of their plastic enclosures he needed a way to soften the sharp edges when they’ll be pressed against your ears. Sugru once again shows its versatility by providing a soft, self-bonding, and moldable surface. The last step is dead simple, as the ear warmers already have a fabric pocket by each ear perfect for accepting the speakers.

Now we need this to go one step further, by making them wireless. We figure hacking in a bluetooth headset board would make it work with your cellphone. Or you could roll your own minimal MP3 board and house it in the part that wraps around your neck.

Bluetooth headset battery swap keeps going and going…


[Reginaldo] purchased a cheap Bluetooth headset adapter, and while it worked well with all of his devices, he was disappointed to find that the battery life didn’t quite live up to the manufacturer’s claims. Advertised as capable of operating for 10 hours, he discovered that the device would typically die after only 7. He wanted more from the headset, so he took things into his own hands and replaced it with a much larger battery (Google Translation).

His goal was to keep the modifications as cheap as possible, so he repurposed a lot of items he had sitting around the house. He used a battery out of an old cell phone, with a capacity over six times greater than that of his original headset battery. He built a charging circuit using a MCP73863 microchip, specifically designed for managing Li-Ion/Li-Poly batteries. The Bluetooth headset was dismantled and repackaged in the shell of a cheap “audio amplifier” that he had on hand, along with the new battery and charging circuit. A nifty Hackaday logo was included on the outside of the new battery case, and the project was deemed complete.

[Reginaldo] reports that he is quite happy with his battery retrofit. The new power brick only takes about half an hour longer to charge, but can now be used for approximately 44 hours before requiring a recharge – not too shabby!

Headphones use standard-sized but proprietary rechargeable batteries

Here’s something we haven’t run across before. We’re familiar with proprietary battery shapes (we’re looking at you, digital camera manufacturers), or custom recharge connections (look of death directed toward cellphone manufacturers), but using electrical tricks to force AAA brand loyalty is a new one. It seems that’s exactly what is happening with [OiD's] wireless headphones which were manufactured by Phillips.

The headphones take AAA sized batteries and can use either disposable or rechargeable varieties. There is a warning label advising that only Phillips brand rechargeables should be used, and sure enough, if you try a different brand the performance suffers both in charging time and in battery life. The original batteries are labelled as Nickel Metal Hydride at 1.2V and 550 mAh, which falls within common specs. But [OiD] noticed that there is an extra conductor in the battery compartment that makes contact with the sides of the battery case. Further inspection reveals that a reverse-biased diode makes contact through this conductor with a portion of the battery which has not been painted. This is not true with other brands, allowing the circuit to distinguish between OEM and replacements.

[OiD] shorted out that connection and immediately saw a performance boost from his replacement batteries. It’s hard to know exactly what’s going on here without a full schematic for the circuit, but we’d love to hear your speculation on this setup in the comments. Is this a low tech version of the identity chips that camera batteries sometimes hide?

Audiophile quality headphones at a fraction of the price


If you are in the market for a nice pair of Hi-Fi headphones, it is not uncommon to to find price tags in the range of $300-$500. [Stacy] loves her music, but she had no desire to pay that high a price for a pair of good portable cans. Instead, she upgraded a set of cheap, knock-off headphones to near-audiophile quality for less than $50.

She starts off by explaining the technology behind the expensive headphones you see in stores, and why the sound quality is so much better. She says the orthodynamic drivers used in these products produce far better sound due to the placement of the voice coils, and their lack of delay when producing sound.

She found a pair of orthodynamic drivers for $30 and fit them into her knock-off headphones with a reasonable amount of effort. A bit of insulation and supporting plastic was added to ensure proper mounting of the drivers, then the headset was painted and reassembled.

[Stacy] claims that the end result is easily comparable to far more expensive headsets, especially when connected to a proper amplifier. If you are looking to step up your audio game on the cheap, here’s your chance.