A NEW MintyMP3, anyone want to help?

[magician13134]

Hey everyone, with my Science Fair due on Saturday, and being a second semester senior, I will soon have very little to do. So that got me thinking that I should do one HUGE project before I graduate. As I'm sure you've gathered from the title, I chose an MP3 player. As far as I can tell, there are enough resources online to make this possible. Here's what I'm thinking, it will essentially be a modified Arduino (we can cut back on space by using a mini-B type USB connector and removing unnecessary components like the programming header), either run by two 'AA's boosted to 5V or a lithium battery, a CF card for storage, an MP3 decoder chip and top it off with a TouchShield Slide for 320x240 gorgeous pixels of touchable action! With resources from Arduino, Boarduino, MintyMP3, etc. I think it would be easy enough to mash this together to fit into an Altoids tin. From past experience, I know it's cheaper to order several PCBs at once, so I was thinking that anyone who was willing to help could get a free (set of) PCB(s) when I ordered them. Does this sound like a good idea?

[Mute]

I like this idea, as making an mp3 player is on my list of things that I want to make. So I would love it if you decide to build this, if you would go through the whole build process. I would appreciate that.

As for contributing to the thread, my suggestion would be to use Shapelock for the chassis. Instead of trying to cram everything into an Altoids can. But, of course it would cease to be a "minty" mp3 player at that point.

http://shapelock.com/

[magician13134]

Hmm, that looks very similar to PolyMorph. I've never really had great success with that. Personally, I think the Altoids tin would be possible, not to mention awesome.
My main concern is the height. If we used an Arduino-sized board, it would fit horizontally with .125" left over, but the other side would have almost an inch to work with. Since using the lithium backpack (which would be REALLY nice) in addition to the TouchShield Slide would put it above 13/16", I think we would need to fit the battery BEHIND the Arduino, where it would have .925"x2.25". So to do this, all of the components (ATMega, USB interfacing, charging circuits, CF/SD card circuits, and MP3 decoding would have to happen on an Arduino-sized board. Seeing as most of that happens on the MiniMinty, I'm fairly confident it could be do, it's just a matter of most likely using several SMT chips.

[Amberwolf]

PolyMorph and ShapeLock both look like versions of Friendly Plastic I used to use for sci-fi props a couple of decades ago. It works great, and can even be removed from electronics after you've put it on (by melting it in a double-boiler, since it floats and the electronics usually sink), and is very hard and resilient at first. Unfortunatley after exposure to UV (sunlight, especially), it tends to get fracturable, and cracks or shatters when dropped on hard surfaces. So I ended up potting the electronics in silicone, and *then* putting FP around them, for things I didn't want to have to cast things in molds for, but rather to hand-shape (great for ergonomic designs, since you just mold it with your hands to fit the way you want, before it cools too much).

Another problem with it is that since it is meltable by low heat, leaving it in a car in summer is a REALLY bad idea.


As long as you can do the work with SMT, it should all fit. It may take some creative routing of traces around the board to get it all as compact as possible, including components on both sides (primarily to use the SMT caps and resistors as jumpers across traces that would otherwise require either more layers or more plated-thru-holes for going around things).

A Li-Ion or Li-Poly battery would save a lot of space compared to boosting AAs or even AAAs, and net you a lot more power, I think. If you can get a LiFePO4 battery in the flat pack size you need, it will be even better, because it isn't going to potentially destroy everything if something goes wrong with the charging circuits or battery, or if it gets wet/etc. Unfortunately it doesn't have the same power density as the others.

I've done a very very little searching for this type, and haven't found them yet, just what are listed as Polymer Li-Ion or Li-Poly flat packs, such as the ones here:
http://www.batteryspace.com/index.asp?P ... tegory=869
and here:
http://www.batteryspace.com/index.asp?P ... egory=1338
(these two pages used because there are images of lots of shapes/sizes, and a table of measurements and weights)
I wanted to use them for my bike helmet lighting, if I could find them, but all the LiFePO4s I've so far found are typical cylindrical cells.

There are also places that sell just the BMS boards for these batteries, such as here:
http://www.batteryspace.com/index.asp?P ... egory=1356
(since I was already at the site for the above, not recommending any specific place)
So you don't have to design your own. But you can do so if you want to integrate the BMS/charger into the rest of the main board.

There are also of course the standard battery packs already made with built-in BMSs, such as celphone or other devices' replacement batteries. (in fact, old batteries from such a device are a place to get BMS boards from, to use with bare batteries for experiments, if you need to).

[magician13134]

Thanks for the links. I think in order to keep prices low, it would be in the best interest of the project to forgoe the touch screen and replace it with something like this:
http://cgi.ebay.com/132x132-pix-Serial- ... 1|294%3A50

Also, can anyone tell me if this is just a trick of perspective, or are these different sizes?
http://www.adafruit.com/index.php?main_ ... cts_id=123
http://mouser.com/Search/ProductDetail. ... bWcg%3d%3d

(Also, is there an Eagle library, or pin-to-pin compatible library for that? Preferably SMT)

[eil]

I wish I had the time to contribute, but I'll be keeping an eye on the project from a distance. :)

Also, can anyone tell me if this is just a trick of perspective, or are these different sizes?

Mouser tends to use the same photos for parts like ICs that have a similar external appearance. Just pay attention to the part number and pin count and you'll be fine.

[nphillips]

I wish I had the time to contribute, but I'll be keeping an eye on the project from a distance.

Me too. I don't have the time/skill to contribute right now, but if you bring it to completion and are selling PCBs, I'd buy them in a heartbeat.

Personally, I think the touchscreen is "unnecessary" but I'm not against it. (heck I still use a 3rd Gen iPod with Rockbox. If it plays my music, and I can browse by common id3 fields, I'll love it)

[magician13134]

Yeah, the touchscreen is out, but It's very easy to use, so I'll try to leave the necessary pins to plug that in and a bootloader for people to upgrade code if they want to add that. The developer of Daisy MP3 has agreed to help a bit as well, so that should really help quite a bit

And if this is a kit, would you WANT to solder on surface mount parts, or prefer that those are presoldered (just the hard ones, like Ladyada does with the USB-Serial converter on the Boarduino kit)?

[eil]

I think you're going to have a hard time finding through-hole parts for something like an MP3 player and if you could, they would probably increase the size of the whole thing.

Surface mount soldering isn't that scary anyway, once you're comfortable wielding an iron. My method is to simply blob the solder on and wick it back up.

[magician13134]

I'm not looking for through-hole parts (except perhaps resistors, caps, etc.) but I COULD have PCBs come with the really hard ones presoldered, if that's what people wanted. But I'll cross that bridge when I come to it

[nphillips]

I, personally, have NO experience with surface mount soldering.

That being said, I think I'm rapidly approaching the point at which I'll need to give it a go...you can only cram so many parts into a small space before running out of room

Also, if you're interested, I would certainly love to help the project out with the UI-side of things. I might not be able to program it, but I could definitely get layouts, graphics, etc. done

[trialex]

Don't be too hung up on running at 5V.

AVRs (including the arduino AtMega168) can run on 3.3V - especially if you use a low power version - i.e. like the lilypad without a crystal/resonator and running on the internal 8MHz. You get power savings by running slower.

I am assuming you will be using both a VS1XXX series chip for mp3 decoding and an SD card for storing the files - both of these are native 3.3V. By runnning the processor at 3.3V you save the hassle of interfacing 5V parts to 3.3V parts.

Finally by not "boosting" the battery by as much or at all, you reduce/eliminate the inefficiency factor of the boost circuit.

[trialex]

All that said, I'm definately up for helping out. I've often tried to plan out a homebuilt mp3 player. I can understand all of the electrical/physical interfaces, but I really don't understand the data interface - i.e. how do you get the mp3 file data chunks into the mp3 decoder chip?

I think this is a fairly in depth project. I would tackle it in stages, and i think you'd actually find a "market" for PCBs and/or kits at every stage.

[1] Get a really basic version working first, no screen, no usb interface. provide acess to the serial port using a standard FTDI pin-out so that you can use a FTDI cable to re-program it (same as original boArduino). Essentially consists of the three main components: AVR, VS decoder, SD card, plus supporting resistors/capacitors, an on/off switch, and four buttons (start/stop, next track, volume up, volume down).

This would essentially be replicating the Make: daisy player - but of course using the AVR. Goal should be to come in under the daisy price, which is something rediculous, like US$100

[2] include an LCD - a small colour mobile-phone style.

[3] include a lithium battery + onbard recharging circuit, move USB on board for both charging and re-programming. I don't think you will ever get USB file transfer going without changing the processor.

Stage 3 would essentially be replicating Sparkfun's mp3 development board - http://www.sparkfun.com/commerce/product_info.php?products_id=8603

This was a long post - hope you read it all.

[magician13134]

This was a long post - hope you read it all.

I wasn't that long
Anyway, I was planning on doing most of the first two steps on a breadboard, but we'll see how it goes. And yeah, data transfer, even if accomplished would be deathly slow, and with an SD card, there'd be no reason to not just pop out the card and load it up with songs.
I too am mostly daunted by the task of reading the SD card, I'd LOVE to be able to list folders/songs or even group by ID3 tags. But that's to come way later, which is why I think the USB will simply be there for charging and updating the firmware. Science fair is tomorrow and I have three AP tests today, but once all that weight is lifted from my shoulders, I'm going to dive in head first
I'm quite excited about this!

[magician13134]

Alright! Engineering fair is over (my partner and I got first place and are going on to the city-wide fair ) and I'm ready to start this. I've never really thought about this before, but I think it's something that needs to be considered; what frequency does this need to be? I read up a little bit on the MIntyMP3 and it said that v1 ran that 20MHz and v2 was 29.4912MHz? The chip I'm ordering (Mega328) says 20MHz, but that's always confused me, does that mean I can't use higher than that? Or does it mean that for higher frequencies I'll need an external resonator/oscillator? I looked through my resonator drawer and found some "20.00MX", will that work? Thanks

And I'm having trouble finding good, cheap switches. On the MintyMP3, there's those nice right-angle switches and that very cool (I'm guessing) volume control switch... Does anyone know a good brand of those? Preferably on Mouser?