I haven’t worked on this in a while, but the circuitry I proposed was for a voltage monitoring and safe shutdown and startup. The AM3358 already has a watchdog timer and will reset the board if the watchdog is not serviced in a predefined period. My proposed circuit included supercaps to power the board during power failure so that the board can shutdown safely. You need a state machine to deal with all the corner cases, such as 1) what happens if you have a power fail, you trigger a shutdown and then the power is back on before the shutdown completes. In that case, you have to power off the BBB, wait for the supercaps to charge and then reapply the power to the BBB. 2) what happens if the power is on and the board begins to boot, but then the power fails before the board has completed it’s bootup.
There are several more corner cases when you think through all the scenarios. Also, you need a supercap charging circuit since supercaps are normally rated at 2.7V so you have to put them in series but one supercap may have lower impedance than the other so one supercap may exceed it’s max voltage and may in fact go negative during discharge. Your charge circuit must prevent both conditions. You will also need a boost regulator to keep the voltage on the processor constant as the supercaps discharge. Lithium batteries would be easier, but then you are faced with the limited number of charge cycles and the limit life expectancy of these batteries. Just some ideas to think about. Regards, John > On May 15, 2016, at 1:07 PM, Super Twang <supertw...@gmail.com> wrote: > > > > I've just come across this conversation in my own search for a rock-solid, > embeddable configuration for the BeagleBone Black. I’m trying to develop an > embedded controller device that needs to live behind walls, in ceilings and > in other inaccessible places. ( It is for the automation of art & other > electronic installations.) > > From what I gather here, the BBB is not quite up to the task, without an > external watchdog circuit (please correct me if I’m misreading this thread). > > @John3909: Your suggestion of the GreenPak prompted my own discovery of that > tech — it looks great, esp the ecosystem of tools around the platform. > > In looking around, I found some Silego application notes that implement a > hardware watchdog for MCUs. > http://www.silego.com/products/352/312/AN-1058.html > <http://www.silego.com/products/352/312/AN-1058.html> This might be a useful > starting point for anyone using GreenPak for a hardware watchdog. > > @John3909: Does this design look like it might be a good fit for the BBB? > (Not knowing how to read GreenPak internals, it is not obvious to me) > > Alternately, I'm wondering in the two years that have passed since this > thread started, if anyone has developed a hardware watchdog design for the > BBB they'd be willing to share. An open-source hardware watchdog for the BBB > would go a long way towards ameliorating the hardware issues with the PMIC on > RevC, and allow it to prosper as a base for applications where long-term > reliability matters. > > Although I’m first and foremost a software engineer, I've got some > electronics chops (albeit mostly digital), but (sadly) very limited hardware > design equipment (oscilloscope, etc). [That said, I have iron, and will > solder!] I’d be happy to develop & contribute the software components for > such a system (I’d envision a library + device tree overlay) if someone(s) > else would like to partner up to design the hardware side. > > Best, > > ST > > > -- > For more options, visit http://beagleboard.org/discuss > <http://beagleboard.org/discuss> > --- > You received this message because you are subscribed to the Google Groups > "BeagleBoard" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to beagleboard+unsubscr...@googlegroups.com > <mailto:beagleboard+unsubscr...@googlegroups.com>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/beagleboard/c7fb39d8-84ef-4127-9db8-cd65a6965e31%40googlegroups.com > > <https://groups.google.com/d/msgid/beagleboard/c7fb39d8-84ef-4127-9db8-cd65a6965e31%40googlegroups.com?utm_medium=email&utm_source=footer>. > For more options, visit https://groups.google.com/d/optout > <https://groups.google.com/d/optout>. -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/5F4B57BD-6AB4-4DFF-ACDB-66C038778EC3%40gmail.com. For more options, visit https://groups.google.com/d/optout.
