Powerdown GPIO?


#1

Hi in playing with solar systems I’ve come to the conclusion that Solar panels are simple and reliable and cheap, and batteries are expensive and unreliable and evil.

I’d like to direct power my Dreamcatcher from a ~60w solar panel, used with supercapacitors for a clean shutdown.

Is there a GPIO to do this? If not could you consider adding it to the next iteration?

I think it would be a real bonus in challenging remote locations where batteries will always fail. Such as remote schools in Africa etc.


#2

The current dreamcatcher v3.03 is pretty much a development board with lots of vulnerable points and pin, but no standardized gpio’s like other sbc boards.

My guess it the next version will have even less accessible stuff…

I have down-powered my dreamcatcher hundreds of times without using the reset/shutdown switch or the lcd shutdown. I have never had a corrupted sd card and it has always come back once power is re-applied. So… my recommendation is just let the dreamcatcher shut itself off on low voltage from a solar array/battery (or capacitors).

Also if the ‘shutdown’ button is used on the current board… it sometimes requires that it be pressed a second time to ‘restart’ the dreamcatcher (depending on if power was lost or for how long).


#3

Thanks that’s useful to know.

I’d still like to make it a feature request for the production hardware. Eventually the SD will get corrupted. Not such a big deal here, but if you’re 35km from the nearest paved road in Sudan…

With a good solar / capacitor setup these things could last a really long time. 15? 20 years?


#4

Hi Sam - - this may be useful information. I use an EasyAcc 20,000mAh power pack on my Dreamcatcher. I have it continuously plugged into a USB charger. It works as a true UPS if external ac is removed and reconnected if it has enough charge saved. It typically runs my DC about 15 hours with a 1 amp draw when external ac is removed. Oh yes - - pulling the plug to power down the DC 3.03 has not created any problems for me.

I believe a couple of other Forum members have successfully connected a large solar array to keep the EasyAcc fully charged. Maybe they will respond to this post. Ken


#5

Hi Ken

Thanks for that. I still have a personal dislike of batteries! They always fail.

A direct solar/capacitor setup would only work in the daytime, but should work over a 10+ year horizon.

Maybe one option is to just supply each field-deployed unit with a set of three preconfigured spare SD cards for when they fail…


#6

regarding supercaps and life-span. Elevated temperatures accelerate their life. While this is true with any electronics, I think it’s more pronounced in supercaps. I worked on a project many years ago that used Maxwell supercaps as a short term backup. I sent the yearly temperature profile of the area, plus the expected heat-rise in the enclosure, to Maxwell. They computed an expected life-span of about 7-8 years, where as I recall “end of life” is when actual capacitance value loses 20-50% of initial/rated capacitance.

A quick example operating at 85*C (super hot, but gives the idea). An electrolytic can be rated up to 2 years, whereas a supercap is rated for about 40 days under the same conditions.

I think the solar/super-cap is a cool idea. Just wanted to share my prior experience on expected lifetime that I had on a directly related project that used supercaps.


#7

Is there a GPIO to do this?

Most of the DC3’s GPIOs are used to toggle things, such as LEDs (eg enabing SD2 LED in Armbian via custom DTB), or the LNB. I have not poked around enough to check if the “PC##” pins on the board are actually GPIOs.

Considering you want a GPIO to shut down when the power is low, you must have a way to read capacity. In such a case, perhaps the serial console (lvttl) could be repurposed for your needs.

Also if the ‘shutdown’ button is used on the current board… it sometimes requires that it be pressed a second time to ‘restart’ the dreamcatcher (depending on if power was lost or for how long).

Based on the linux kernel code and the Device Tree Binary, this button mimics a standard PC’s ACPI.