70 watt amp uses an ATtiny

If you’re looking for a DIY amplifier project made with a minimum of parts, this is the build for you. [Rouslan] created a 70 watt class D amplifier using an ATtiny45 and just a few dollars worth of additional components.

A class D amplifier simply switches transistors of MOSFETs on and off very rapidly. By passing the signal produced by these MOSFETs through a low pass filter and connecting a speaker, a class D amp is able to amplify a signal very efficiently. Usually, these sort of amp builds use somewhat esoteric components, but [Rouslan] figured out how to use a simple ATtiny microcontroller to drive a set of MOSFETs.

In [Rouslan]‘s circuit, the audio signal is passed into the analog input of an ATtiny45. Inside this microcontroller, these analog values are sent to the MOSFETs through a PWM output. [Rouslan] threw in a few software tricks (explained in revision 2 of his build) to improve the sound quality, but the circuit remains incredibly simple.

[Rouslan] posted a video going over the function of his ATtiny amp, and from the audio demo (available after the break), we’re thinking it sounds pretty good. Amazingly good, even, if you consider how minimalistic this 70 watt amp actually is.

Thanks [Alec] for sending this one in.

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Outdoor stereo helps your neighbors learn to issue noise complaints

Backyard parties are going to rock over at [Effin_dead_again's] house. That’s because he just finished building this outdoor stereo. It carries its own power supply so you can take it on the road with you, and we don’t think you’ll have trouble hearing it with the 240 Watt amplifier hidden inside.

He shared the equipment details in his Reddit conversation. A 12V lawn mower battery sits in the base of the wooden enclosure. One of the commenters mentioned the dangers of hydrogen off-gassing from that power source, but [Effin_dead_again] thought of that and included venting around the lid. The subwoofer is an 8″ Alpine, and speakers are out of a Hyundai car. The head unit has Bluetooth built in for easy connection to your smart phone. It of course has the ability to play CDs and MP3s too, and we’d bet you can tune the radio if there’s an antenna connected.

Need similar power but a bit more portability? Check out this stereo built into a cooler.

Pimp my scooter

[Glen] built this shiny party machine out of a pretty sad-looking scooter. We’d bet you’re wondering why we think it’s a party machine when it looks so common? The only real giveaway in this photo is the custom exhaust, but hidden in the body of the beast is 720 Watts of party power plus a whole bunch of extras.

When he gets where he’s going, [Glen] parks his ride and lifts up the seat to unfold the entertainment. Attached to the underside of the saddle is a 720 Watt audio amplifier. It drives one big speaker under the seat, as well as two tweeters and two mid-range speakers that were fitted into the front console. But these days a party isn’t a party without some video, and that’s why you’ll also find a 7-inch LCD screen suspended from the upright seat. Tunes and videos are supplied by an iPod touch up front, or the PC he built into the ride. All it’s missing is a gaming console!

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Surround Sound system controller replacement includes home automation

[Neoxy] always wanted surround sound for his computer, and one day he managed to get a hold of a dead 5.1 system. Why buy one when you can repair someone’s rubbish, right? That turned out to be easier said than done, but after several false-starts he managed to resurrect the audio system by replacing the microcontroller.

We find his trouble-shooting technique interesting. The amp would power up without a hitch but no sound would come out of it. So he took a headphone cable and used the L and R conductors as probes. That cable was fed from an MP3 player, and by touching the probes to the audio inputs for the pre-amp and amplifier circuits he could get great sound out of the speakers. Reasonably certain that those boards were working fine he narrowed down the troubles to three chips that mix, select inputs, and control the system.

A lot of prototyping with an ATmega328 and an Arduino led him to the functionality you see in the video after the break. Not only did he get the system working, but he’s using the Arduino to add Internet control for the device.

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Free formed circuit protected by a brick of crystal clear resin

The look of this crystal clear resin brick is pretty amazing. [Rupert Hirst] decided to encase his amplifier circuit in a block of polyester resin. We just hope he got everything in his circuit right because there’s no way to replace any of those parts now!

He deserves a lot of credit for working out a visually pleasing way to mount each component. There wasn’t any type of substrate used, but a few lower gauge wires were picked as the rails and they add some mounting stability. Before casting, he took the case of each of the three jacks apart and sealed the seams with some of the casting resin to prevent the final pour from filling them up.

Eagle CAD was used to design the mold. He printed it out on some card stock, then used a hobby knife to cut the pieces out and super glue to assemble them. A second layer of super glue was run on each seam to ensure they’re water tight. After the casting was made [Rupert] spent plenty of time sanding, routing, and polishing the brick to achieve this look.

This makes us wonder about heat dissipation. Do you think it will be a problem? Tells us what your opinion by leaving a comment.

SpeechJammer puts an end to annoying speakers

If you’ve ever had to deal with people disturbing your peace and quiet by yammering on with their cell phones, you might be interested in the SpeechJammer.

The idea behind the SpeechJammer is fairly simple: It’s very hard to speak if your words are recorded and played back to you a fraction of a second later. This is a real psychological phenomenon known as delayed audio feedback that also has a beneficial effect on stuttering.

According to the researcher’s writeup (PDF warning), the SpeechJammer works by measuring the distance to the ‘target’ with an ultrasonic distance sensor and records the speaker’s voice with a shotgun mic. The recording of the spearker’s voice is delayed for about a fifth of a second and then played on a speaker on the front of the gun.

The researchers tested two conditions: ‘reading news aloud’ and a ”spontaneous monologue.’ Subjects who were reading news aloud had their speech jammed more often than those with the monologue, but the results look fairly promising. There’s only one video of the SpeechJammer in action (available after the break), so we’d like to see a few Hackaday readers build their own ‘shut up gun’ and send in a demo with an annoying talker to validate the results.

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Rotary phone-light-amp could be filed under bizarre

[Samimy's] latest project is a little strange, but one man’s weird is another man’s wonderful so we’re not about to start criticizing his work. Nope, we’re here to praise the fact that his rotary phone turned reading light and audio amp is very well constructed.

He started by removing the phone housing. Those old enough to have used one of these devices will remember their bulk, and there’s a lot of unused space in both the handset and body housing. [Samimy] started by removing the speaker and microphone from the handset, and drilling a ring of holes to receive white LEDs. The circuit was wired so that lifting the handset turns on the lights.

But he didn’t stop there. A set of speakers and the audio amplifier circuitry from an old tape deck are also hiding inside the base of the phone. If you look closely in the image above you can see that he’s connected his cellphone and is listening to some tunes through the antique hardware. Take a gander at the video after the break to see construction and use of the project.

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