Hello everybody,
I have a GP output of a Beaglebone Green that turns the power off when it is asserted by SW. It does its job well.
However, I would like to power the Beagle off after having done a shutdown (rather than turn it off suddenly).
Is there any SW/HW trick to get this behavior?
Thanks for the attention.
G
Are you talking about something that turns off an external power
supply? On the BBB, and BBAI, "shutdown -h now" ends with the circuits
behind the regulator chip being unpowered.
Anything cutting power to the board itself likely needs to have a sense
lead (maybe to one of the 5V header pins) which holds the power supply
"active", and opens when it loses the 5V. Of course, that also implies one
would need a momentary contact NO switch to the input of the power supply,
bridging to an always-on 5V source in order to "jump-start" the system
(hold down the NO switch to get the power supply to provide power to the
board, release switch when the header 5V pin feeds back to the power supply
control). Of course, you may have to find some way to prevent any voltage
from the NO switch feeding back to the header pin. Maybe a pair of
transistors -- one transistor controlling the power supply input, with the
control lead shared by the output of the other transistor and the NO
switch; the second transistor controlled by the header 5V pin. IE: this
second transistor in/out is parallel with the NO switch.
Hello Dennis,
I much appreciate your reply.
The point is that I have an external power supply that powers the BB and some other peripheral devices.
So if I make shutdown -h the BB turns off but the external power supply still remains on. This is why I have a GPIO pin on the BB to turn off the external power supply. But I cannot use this pin if the BB itself is off!
Hope it is clear now.
Best rgds,
G
IF you want power supply control like that. You will need a small
low power mcu like an msp430 running off of a small coin cell
to manage power.
You might be able to modify the shutdown script so that the last thing it does is drive your gpio to unset the power supply. I’ve never done that before; we in fact used an msp430 to do what you need and more.
You can probably find more information about modifying the shutdown procedure elsewhere. It would be standard Linux stuff, if anybody has done something like it.
In the old days you could do init 1 to go to single user mode, and then safely power off from there. In systemd labs I don’t know if you can specify something to be the last thing you do during shutdown.
You could also put an RC filter on the gpio output to give you a little time. That’s pretty janky though I think. I wouldn’t sell something like that (well, I probably wouldn’t) but maybe it’ll suit your needs.
Have fun googling!
J
I have the exact same problem and just got an Adafruit Feather processor, RTC and latching relay. These are sitting in pieces on my desk so I don’t yet know if this is a viable solution. My goal is to wake up a BBB once very two weeks for 1-2 hours and to run from batteries for a year, I have a satellite modem, a motor and a few other things to run from the battery packso every bit of power counts. Leaving the BBB to time itself would just about double the size of battery needed. This is going in a place where there’s no energy to be harvested…
Will look into the MSP430 as well.
There’s nothing special about the msp430. Just needs very low current draw in sleep mode. It can wake itself up based on an internal timer, which would save you the power draw of the RTC, but I bet your processor can do that too. You just might have to code the assembly to get it to work as you want.
The piece OP doesn’t need that you do is the ability to wake yourself back up. That requires something else to stay powered up at all times. I had hoped to use the PRUs for this but it was too hard to use then for all the things we needed, so instead we just used a processor we’re comfortable with, the msp.
Have fun!
Thank everybody for the ideas and advises. I think the simplest way will be to make a simplified power management with a low cost uC, that just delays turning off the external power supply, just to give time to the BB to shutdown properly.
Does anybody know if the non used outputs of the TPS65217 (VLDO2, LS1_OUT, LS2_OUT) are available on the expansion connector of BB?
Rgds.
G
they are not