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Building an open embedded audio applicance.

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#1,181
Unfortunately - the BBB PMC hardware design is such that if you remove power without a clean shutdown first you can destroy the BBB. The battery provision is there to help prevent that from happening. The role of the battery is just to give the BBB a moment to shutdown correctly.

I am hoping the BBB designers resolve this in a simpler way in their next revision.
 
#1,182
Russ White said:
Unfortunately - the BBB PMC hardware design is such that if you remove power without a clean shutdown first you can destroy the BBB. The battery provision is there to help prevent that from happening. The role of the battery is just to give the BBB a moment to shutdown correctly.

I am hoping the BBB designers resolve this in a simpler way in their next revision.
Click to expand...

Would this not be a good application for a supercap? Appropriately sized cap could easily supply a couple minutes of power to facilitate an orderly shutdown.
 
#1,183
wlowes said:
Would this not be a good application for a supercap? Appropriately sized cap could easily supply a couple minutes of power to facilitate an orderly shutdown.
Click to expand...

Actually that was one of the first solutions Brian and I thought of using, but after a lot of research there are some problems with the approach.

- it would have a be a huge one.
- It would actually need somewhat more complex charging support than a battery.
- All but the crazy expensive ones are not designed to source as much current as the BBB may require.

In the end the battery is a far more practical solution.
 
#1,184
wlowes said:
Would this not be a good application for a supercap? Appropriately sized cap could easily supply a couple minutes of power to facilitate an orderly shutdown.
Click to expand...
There are now actually affordable ones that could work, now (that changed almost overnight), but you have to manage, in no particular order:
* Max voltage per cap (2V for a 2.5V cap seems commonly recommended)
* Min voltage total (5.5-6V with a linear LDO), requiring that you use 3 in series right off the bat.
* Min voltage per cap. Most datasheets don't say much, but some do specify lower life at low voltage, and others low voltages (like <1V for any length of time) as ignored/undefined.
* That series capacitance could be as low as (rating * min tolerance)/number.
* Discharge limits (often very low).
* Charge limits (even using supercaps made for high charge and discharge rates, you could destroy parts of your charging circuitry, if not rate-limited!).
* Resistance (anywhere from <0.5Ohm to 50Ohm)
* Lifespan (life is typically expressed at 60C or lower, often with surprisingly low shelf life).

Not to dissuade you from using supercaps, if they'll work well for you, or you want to try them because they're cool new toys. But, they need a lot of care in both selection and implementation, so don't make for good default options.
 
#1,193
Russ White said:
When using Miero's distribution - when main power is lost - shutdown is automatically initiated.
Click to expand...
OK, that's great. This means we don't need to implement any special userspace utilities/commands to check power-status, and initiate shutdown - as we discussed last July.
It should be noted, then, that this auto-shutdown feature is hard-coded into the operating system, so it seems that Miero is using all standard Debian kernel patches.
If anyone wants to examine the details of how this is achieved, get the patches from -
https://github.com/RobertCNelson/bb-kernel/tree/am33x-v3.16
and look in /patches/beaglebone/power/

If you wanted to keep your BBB running on battery for a longer period, say until the battery voltage drops below 3.4V, this is not configurable, so your only option would be to add a fully external power management system.
 
#1,194
All patches are on the Botic image in the /sources/linux-3.16.1.patches/patches/botic/ if you want to know exactly how it is implemented.

Also it will be changed a little in the next release, because the shutdown does not work well if you have mounted network filesystem.

But if you want to keep your BBB running on battery only, there will be a way to ignore AC power lost events. It will be then shut down only by battery low voltage event.

But primary reason to have battery here is to protect BBB from damaging itself, because BBB is using TPS65217C power management IC is which is designated for battery-powered system.
 
#1,195
OK thanks. I see in 0006-pm-fixes.patch you seem to have incorporated and refined the Debian 0001-tps65217-Enable-KEY_POWER-press-on-AC-loss-PWR_BUT.patch

I, for one, am reasonably happy with this form of shutdown behaviour, but I suspect others will want more flexibility. So it will be interesting to see the shutdown method in your next release.
 
#1,197
DC when stopping music

Just bought myself a BBB and I hand soldered a cape for the BBB inspired by what is going on in this thread.

I have it up running with Mieros SW and the YMPD test files. I have not dared listening yet as I found something that I have not seen before. When stopping the music the output just stops where it is, leaving DC on the output. Yes, my headphone amp is DC-coupled.

My question is:
1. Is it not common practice to output zeroes when stopping the music?
(I am complete beginner on Linux, would not have a clue how to fix this)

Thank you for making this possible. Really great work done so far.

(( Per
 
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