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 Post subject: Portable Recheargable Tunes v2.1
PostPosted: Thu Jan 30, 2014 10:25 am 
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Joined: Sun Mar 15, 2009 9:10 am
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Location: Golden Valley
So, after using the first version for a few months I've decided to rework the design and put in the features I think I'd like.

The first change is to add a Linkwitz Transform Circuit to allow a bit more bass extension. The goal is to get it down to about 50 Hz or so and I tested the drivers last night with a 55 Hz signal and they survived pretty well. The way the circuit works is a little complicated but the upshot is it artificially boosts the low frequency signal to overcome the driver's natural roll-off. Essentially what this will do is give me some serious bass coming out of a tiny 2" driver. There's a ton of information about this out there and you'll find copies of an Excel spreadsheet that will help you calculate the values you need. But I found an even better spreadsheet that will simplify your design by giving you the choice of using exact values, with components in series and parallel, or using a single "close enough" value component and what sort of deviation from your goal you might expect. http://audio.claub.net/software/LTwithMC/LTwithMC.html (I had already spent nearly a week trying to design the PCB layout for multiple values, and selecting the value of components to put on it, when I came across this. It would have saved me sooo much time.)

In order to calculate the LTC I had to know precisely what the dimensions of the box are going to be. And since I was optimizing I may as well make it as small as I could. The main constraints here are the battery packs and the size of the amplifier board, as well as the width of the BlueTooth decoder. The final dimensions came out to 10.5" x 3.25" x 3", 102 cu in. (The old version was 12.25 x 4.25 x 3.25, 169 cu in. which is a 40% reduction in volume.) It'll be mocked up in 1/4" MDF and cut on the laser cutter. It'll also get a much better paint job and perhaps a grill on the front to protect the drivers and the power switches.

Another upgrade is using a BlueTooth/FM/MP3 USB/SD card decoder, w/ Aux and a remote. I've only ever found them on Ebay, and the price is ridiculous cheap for what it does, $10. It should be arriving today or tomorrow. http://www.ebay.com/itm/400596390388?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 The bonus feature is the USB port can charge your device, but I'm sure it's in the 500mA range, if it's even that high.

I'm considering adding a few super bright LEDs to the front but that might be taking things too far.

Power supply upgrades will be a dc-dc boost/buck converter that can take any voltage from 3-35V in and output the exact voltage I need to charge the batteries. The old charge circuit required at least 14.3 volts input in order to get the 11.6v I needed to charge the batteries, with a 2V drop across the LM317 and a 0.7V drop across the diode. I might be able to really play around with the solar panel voltages with the input voltage this low. The other power supply upgrade is a USB buck converter that can handle up to a 3A output for fast charging. I might be able to add some resistors to put out the correct voltage on the data pins to allow Apple products to use this full amount of output. Another hope is that this will help with the ground loop issues I was having with the initial design. I'll be trying to find some small switches so I can turn off the USB port and the amp and BT circuits.

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 Post subject: Re: Portable Recheargable Tunes v2.1
PostPosted: Sun Feb 02, 2014 1:57 pm 
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Location: Golden Valley
Loads of progress! I figured out Inkscape and made a laser cut box pattern with the tabbed box maker extension, and I added the cutouts for the drivers and the new BT device. I also figured out enough PCB Artist to make my Linkwitz Transform circuit. I'll be trying a couple different ways to etch the PCB, I'll do toner transfer and then try the laser and burn off paint to expose the tracks for etching. There are other ways but I'd like to compare the quality of these 2 methods and maybe run a short class on it later. I think the laser method would be really easy to do 2-sided PCBs as you could easily index the boards and flip them over.

I may try the toner transfer yet today, if I can find my tiny drill bits.

Below are the images for the box, one what I hope it'll look like when it's finished and the other showing all the bits that go inside. The other is a quick shot of the PCB layout with the components showing and the copper pour removed.


Attachments:
PSB v2-1.png
PSB v2-1.png [ 49.97 KiB | Viewed 184 times ]
LTC.jpg
LTC.jpg [ 27.31 KiB | Viewed 184 times ]

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Instructables is my crack.

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 Post subject: Re: Portable Recheargable Tunes v2.1
PostPosted: Mon Feb 03, 2014 12:05 am 
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I'll be interested in hearing how the laser-mask etch goes. I want to use that on aluminum for decorative purposes. I want the cut to be deep enough that I can flood it with paint to imitate the look of logos on cast parts, and figure using palst-dip spray would make the job easy (spray, laser cut, etch, flood with paint, peel off plasti-dip).

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 Post subject: Re: Portable Recheargable Tunes v2.1
PostPosted: Mon Feb 03, 2014 7:15 am 
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Location: Golden Valley
I'll need to research which paint is good for etching, plasti-dip might be overkill. Can aluminum be etched with ferric chloride? I think you'd want to do your etching, clean off your mask, then flood the etched portion with your finish paint. I'm not sure, but it seems easier to me.

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 Post subject: Re: Portable Recheargable Tunes v2.1
PostPosted: Fri Feb 07, 2014 9:55 am 
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Super teeny tiny soldering job is done! I soldered SM components once and I was terrible at it, it worked, but it wasn't pretty. This time I managed to solder not one, but two SOIC chips with a pin pitch of .05" to a DIP conversion board. I did get a solder bridge, but Steven was kind enough to fix it.

I'm breadboarding the Linkwitz Transform Circuit and I'm hoping to be able to test it tonight or tomorrow.

I wish my dang USB buck converters would show up, it's been over a month. But there's plenty to do in mean time.

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 Post subject: Re: Portable Recheargable Tunes v2.1
PostPosted: Fri Feb 07, 2014 10:18 am 
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I at least made you try several times first to clear the solder bridges. Next time to help you improve your soldering skills I may wait until the next week before I tackle they myself :D

I'm looking forward to hearing how the rest of the circuit works out for you! Good luck!

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 Post subject: Re: Portable Recheargable Tunes v2.1
PostPosted: Fri Feb 21, 2014 8:56 am 
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Update:

I breadboarded the circuit but it was very quiet and I needed full volume in order to get the slightest bit of noise from the drivers. I'm not sure if thats due to some bad connections on the breadboard or what, but I'm looking at modifying my pcb in order to add a couple resistors, or a pot, to add some gain before going into the second set of op-amps. Not knowing a lot of electronic theory means I get to experiment.

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