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Misc notes: Solar power for low current projects... or... (several other circuits!)

Includes buffer 'battery' to carry you thought the night, of cloudy spells, and watchdog timer to fix brownout lock ups (filename: PCB269-SolarWBackup-Misc.htm)

This page is a "workbench". There are various bits and pieces here which, one day, will be integrated "properly" into the main pages about PCB269, my board for Nick Gammon's solar power with overnight buffer... and watchdog timer.

A design option... reset how often?

Nick's design, probably wisely, generates a reset signal which you can attach to whatever PCB269 is powering. Under his design, that pulse is sent every morning.

The driven electronics may lock up for many reasons. A reset once a day seems, to me, to be a wise precaution. However, I think the following would be enough to revise the circuit so the reset pulse only arises if the ATtiny on PCB269 shuts down for lack of power from EITHER the supercap OR the solar panel. (At the moment, you get a reset thirty minutes after the ATtiny re-awakens (for a whole 30 minutes) after fails for lack of power from the solar panels... typically, of course, once a day at dawn.

If you "want it all", you could wire things as before (potentially a reset every time Vin (the power from the solar panels, or whatever you are using) fails, and then comes back (for at least 30 minutes)... BUT... if you added a read of one of the unused GPIO pins (there are pads to connect to them from vers 17b28), you could tweak the software in the ATtiny to execute the reset... or not... depending on the state of the input.

If you are not using solar for your ultimate supply of power, and you want an "every day" reset, you are in trouble. If you set the ATtiny up to do some kind of countdown, then it will be using much more power than it does under Nick's design.... even when running off the supercap. (You will need to remove the "sleep- after- reset- sent" provision from the ATtiny's software.) (But if you want something "standard" like that, why not use a standard watchdog timer chip?)



I've presented Nick Gammon's circuits quite fully elsewhere.

Here are some of the circuits I drew, from his designs, in the course of making the PCB.

They should be "copies" of Nick's circuits. However, mistakes may have crept in. Happily, I use the excellent of the free, multi-platform "EDA" package, KiCad. (Link opens Wikipedia page in new window. Just close it to get back here.)

Because I use KiCad, it is not hard to ensure that the board artwork and the circuit schematic are "in step".

First a recent form of the circuit's schematic. Although the circuit (and board) exist "in" the computer, at 27 Jan 18, no boards deriving from that have been produced yet.

Further down the page: an early version of the schematic. I include this in case it is easier to see the connection between it and Nick's circuits. The early version is complete with the error that makes cutting a trace necessary. It was the basis of version 17b28 of PCB269.

It is probably a little hard to read in your browser. Right-click, use "save image", open the file in a suitable program on your computer.

(Below)- Schematic which is basis of vers AFTER 17b28... likely to remain named "vers 18124".


(Below)- Schematic which was basis of vers 17b28... and much of earlier version, too.


The following is a re-drawing, and where I was when starting work on the version of the board to follow vers 17b28.

There MAY have been changes between what you see and that board when it eventually emerges. However, apart from fixing the mistake indicated above, I don't think there were "changes" other than re-arranging things into a more logical (if less close, in layout, to Nick's originals).

A pretty picture

I produced this for my own wants. It is an image of the version 17b28 board.

The magenta "x"... half way across, 1/3 down... between "R1" and "C5" labels... is where you should cut the trace to fix the error in this design.


This is "scratch" page

Please remember... THIS is a "scratch" page. A place to "temporarily" post things which will, if the project seems of interest to sufficient people, be moved to better places in my set of pages about PCB269, Nick Gammon's solution for powering small devices from the sun, but with overnight power too.

Please get in touch if you discover any flaws in the board, or any ways to go wrong. How are using it would also be of interest.

If you found this of interest, please mention in forums, give it a Facebook "like", Google "Plus", or whatever. I've almost given up writing these pages, because it seems they are seldom read, and of course not every reader will use them... so... is there any point? If you want more of this stuff, help!?

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