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Custom MP3 Player

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amachronic:

--- Quote from: 7o9 on June 22, 2024, 02:03:53 PM ---
--- Quote from: amachronic on June 22, 2024, 12:33:35 PM ---I do plan on releasing the PCB and case designs as open-source once I get closer to finalizing them.

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Sounds very interesting!

Do you plan do some sort of batch of assembled devices too? I would be happy to support that.

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Yeah, if there is enough interest then I don't see why not, but I haven't put much thought into how best to do it so I'm open to suggestions. For a low enough volume I'm happy to order a bunch of PCBs pre-assembled, put them in cases and ship them myself, but for any significant number of units that isn't practical.


--- Quote from: speachy on June 22, 2024, 05:11:16 PM ---
--- Quote from: amachronic on June 22, 2024, 12:33:35 PM ---For what it's worth I've been working on an STM32H7-based design using external SDRAM, also targeting an iPod 6g-like form factor. These are the specs:

* STM32H743 @ 480 MHz
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Sweeeeeet.   FWIW I am particularly fond of the STM32 family, and that has only grown the more I've had to deal with the competition....


--- Quote from: amachronic on June 22, 2024, 12:33:35 PM ---I'm planning on a 320x240 LCD over SPI, which is maybe not ideal

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Given the STM32's DMA engine(s), we could probably just have it on a continual (double-buffered) refresh cycle.  At 320x240x16bpp, 25MHz 1-bit SPI would net us about 20fps.  If we can get 2 or 4-bit SPI that ought to scale nearly linearly.
 

--- Quote from: amachronic on June 22, 2024, 12:33:35 PM ---Compared to speachy's wishlist I am missing a few things (UHS-I, OTG, separate line-out port, 60 FPS display) but they aren't showstoppers and could probably be added in a future revision. Only UHS-I is really a pain, because then you need a level shifter + 1.8v supply on the board, and most of my parts require 3.3v.

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Yeah, no 1.8v supply does hurt. What do you intend to do for power/battery management?  (And not having UHS-1 won't really be visible except when doing file transfers...)

I look forward to seeing what you come up with!

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I think the power circuit will (vaguely) be a battery charging IC + separate buck converters for the digital/analog domains + an LDO to keep the RTC ticking while otherwise powered down. And I'll likely want some FETs for switching things on and off, like the audio circuit. I haven't decided yet if I want to try doing CPU core voltage scaling in this revision but I was intending to. For actually powering on and off I'll have to use some wired-OR type of arrangement -- the power button and a GPIO will both hold power open, but it can only shut down under software control. In case the CPU hangs I can link that GPIO to a timer/PWM output so it will power down unless the timer periodically reset. Without a PMIC or a helper chip I don't think there is a way to have the power button do anything special when held down for a long time (except maybe some analog trickery -- like slowly charging a capacitor).

The battery will either be a generic LiPo cell, probably with a JST connector for easier replacement, or the Nokia BL-5C, which are both relatively easily available. Cylindrical cells would end up making the case really bulky or require cutouts on the PCB (and still make the case fairly bulky) so they're not really a practical choice, unfortunately.

vapre:
I am interested. Are there any plans for bluetooth audio?

redblade8:
This would be cool indeed. Things I look for are microphone recording, and FM radio recording, possibly AM radio.
Another good one would be an external speaker.

Thanks for reading :D
- Red.

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