E-ink calendar and ToDo list

On Fri, 17 Dec 2021 11:44:28 +0100, Giangi72 snipped-for-privacy@invalid.net declaimed the following:

It is an embedded microCONTROLLER -- no OS (unless one ports FreeRTOS to it; FreeRTOS is /not/ an OS as you may think, but rather a real-time kernel that allows for priority-based threads within the application. I don't think your application needs threads/processes -- unless WiFi/network stack needs one). The installed application runs out of flash memory, it doesn't get loaded into RAM before it can run -- so basically, the application runs as soon as the processor initializes. That would simplify a power cycle mode (you'd still have to figure out how to time a start-up sequence -- though some may have a sleep mode using a separate clock chip to wake up).

The R-Pi is a full COMPUTER with high-level OS. It is not considered "real time". It has user accounts/privileges/etc., separation between application and kernel operations.

While the basic Arduino is an 8-bit AVR, the old Arduino Due (and some newer models) use 16/32-bit ARM chips and have more RAM (RAM is basically only used for variable storage -- basically a large register bank). AdaFruit Metro M4 is also an ARM based board with Arduino Uno pin-out. Native mode is that a (Circuit)Python interpreter runs as the main application, with user program loaded into a separate flash area. The Grand Central board has the layout of an Arduino Mega. You can replace the circuitPython interpreter with an Arduino type boot-loader, and use Arduino IDE for programming.

Biggest drawback is that many do not have native networking/WiFi -- so one needs an add-on board for network connections, and applications need to include the suitable libraries to manage the network traffic; it is not part of some amorphous OS. (TIVA TM4C1294 launchpads do have Ethernet, but one still needs to use a library linked into one's code).

And all of these would benefit from an add-on battery-backed up RTC (microcontrollers don't even attempt to keep "wall clock" time; they just count clock ticks from last boot up).

On Fri, 17 Dec 2021 13:41:14 -0000, John Aldridge snipped-for-privacy@cantab.net declaimed the following:

Probably closer to a motorcycle battery <G> for the 10-20Ah 12V. Motorcycle batteries can be picked up in one hand.

Might want a deep discharge model (trolling motor style), but those will be full (car) battery size. Regular (starter motor) batteries are designed for high current draw over a short period of time -- 100+ Amps for

Charging Li-Ion batteries is not simple, advanced charging circuits include temperature sensors to detect when the charge has peaked and avoid overheating the battery.

Calling without a sleep time means it only wakes on an external event

In cars perhaps. Not at lower capacities. Temperature sensors do not detect 'when the battery has charged' on Li-Ion. Voltage detects that. The temperature sensors on big vehicle packs are there for safety, in case a cell goes bad and overheats.

The very simple 'charge each cell at less than the hourly rate to 4.2v and no more' algorithm dominates hobby chargers.

The R/C model community has all the bits and pieces to charge packs and the requisite circuitry to drop the voltage to 5V for avionics - or Pi - usage. e.g.

Put that lot together and you have a system that will deliver ~5V/1A average for as long as the mains is on, and for about 10 hours if the mains goes out.

It's possible...it's just a matter of figuring out how big a battery pack would do that. Someone else theorized that a pack built of 14500 Li-ion cells (two in series, presumably, through a buck converter to get 5V) might run a Raspberry Pi 3B+ for five hours. 18650s are more common and larger; for sake of argument, let's say you get 3x the runtime (2400 mAh) from an

Whether a pack made of two dozen 18650s would be too large for your application is a question only you can answer. :)

I wouldn't advise it! Once you start stacking up large numbers of batteries all sorts of load balancing issues become apparent - both for charge and discharge.

Quite, Unless you've got some cutting-edge chippery that can run for months of a 2032 coin cell, there are only about two sensible ways to go:

- the DCF77 German sime signal with Conrad part number 641138-92 as receiver

-

- one of the US time sources, WWVB or WWVH

I've used Jonathon Buzzard's receiver and Rugby in the past: its 'just worked'

I've also used GPS time - older Puck-style receivers can be picked up in FleaBay. They normally use an RS-232 serial connection as output, and good, inexpensive RS-232->USB adapters are easy to find.

The benefit of of these time sources is that it doesn't matter if your calendar does get killed by a storm or power cut: when power comes back the system can re-boot and re-establish an accurate time in a few minutes at most. also, it will still work if the power cut took out your section of the internet.

The OP wants to display their Google Calendar and todo list in a frame on their wall. That requires an internet connection. You can't display the appointments in their calendar without fetching it from the internet - you could only have a generic day/date calendar which is not what they're asking for. I suppose you could cache the calendar in case the network goes down, and a third party time source would help with bring that back up, but that's a fairly niche use case, and no help if the calendar is later changed.

And so the problem is that the OP needs an internet connection but the power consumption is too high to run a Pi full time unless the battery is implausibly large to mount on the wall. The key is thus turning things off

- either running a Pi on some kind of timeswitch, or using something that is better at entering a low power sleep mode.

Finding out the time is not the problem, getting the calendar updates is. The dilemma is that something that can handle the complexity of talking to the Google servers is probably not low power enough to run from a battery in a wall frame for a week/month/year. Which is what makes me think a two-box solution is the way forward.

Theo

Yes, that or using a UPS with a smaller 1-2 hour battery, which probably would keep it up indefinitely with mains power thats as reliable as here or in most of the EU.

That's not true. All my calendars are local to my phone and not synced to anything not fully under my control. I regularly save backups over my LAN at home and could import that to any other local calendar.

In the present case you do have a point though, unless the OP is satisfied with having his appointments on the wall at home and nowhere else. But that too does not need the internet. Syncing between the (presumably) phone and the wall box over the LAN when at home would suffice.

The OP did specify *Google* calendar - which I rather think does require a public internet connection.

There are of course other solutions that do not but from the perspective of a battery powered, wireless device on the wall it makes no difference whether the data is on a local server, at Google or elsewhere it has to be accessed using IP - in other words over an internet connection and it makes no difference whether the scope of that connection is global or local.

Like I said, the OP's calendar lives on Google Calendar. You can't fetch that without internet, because that calendar lives in the cloud. You can sync to something locally (a server/phone/another Pi), and then the wall frame fetches from there, which is the two-box solution I suggested. If you want a one-box solution you need internet on your one box, there's no getting around that.

You can of course have a wall frame without an internet connection, to which you enter calendar entries on a touch screen or SD card or whatever. But that is an entirely different problem from the one the OP asked for, which was something to show live updates from their Google Calendar. As is worrying about getting the time from GPS, which is also a problem the OP doesn't have.

Theo

Quite so, and the easiest (but expensive) way to achieve a one box solution would be to use an off the shelf e-ink tablet such as a Likebook, but given that they have a display in hand to use and want to DIY the ESP32 option being explored elsethread seems to fit the requirements.

Not really. not for parelleling.

The charge/voltage curves for cells are all similar, what differs is their capacity , so you might think it a problem as some cells charge up sooner than others, but that doesn't matter except at very high charge rates, because the same voltage represents the same state of charge for all the paralleled cells.

But lithium batteries up to 10AH or even more are available. And at 14v nominal that's 140 Watt hours, and a Pi is about what - 5 watts or so?

Or a car battery at 12v/70Ah nets you 160 hours

Forget voltages and architectures - that's all soluble, just pick a battery that has the capacity you need and is happy to be trickle charged at slightly more than the Pis power draw.

Pi draw is roughly 5W. a week is 7x24 = 168 hours

At 12v nominal that is 70 A/h which is spot on for a car or caravan battery.

Looking at lithium cells I cant find a pack at less than £100 that comes close.

So at least you know what you will be dealing with. A car or caravan battery.

And then the problem resolves into how to step the voltage down for api

- but that trivial - the amount of car to USB power converters is enormous, and likewise mains to trickle charge a caravan battery is off the self.

Once you reach the point where the battery is too large to fit within the frame on the wall, you either have to re-think whether a dangling power cable is acceptable, or use something other than a Pi ...

Well exactly. peole seem to think that engineering is how to make stuff work

Mostly the theoretic side of engineering is there to show you what stiff can never work, so its crazy to build it.

Hasn't stopped renewable energy though, but then they never bothered to analyse it, they just built it for profit. irrespective of whether it worked or not.

Perhaps I misunderstood, or at least understood differently. For you a Google calendar is a calendar maintained for you by Google in their cloud. For me it's the calendar app in my phone and provided by Google.

The only really crazy item on the table right now is so-called "Blue Hydrogen": the energetics of making it mean that burning coal is less environmentally damaging than making and using the 'Blue hydrogen'.

I beg to differ. Everything on the table right now is crazy. I've spent many years analysing it, and the only thing that will actually work, other than a 97% drop in population and a return to the sort oft technology the Greens would understand. Presumably horses whose methane emanations would be forgotten in their sheer organicity... is nuclear power of some sort.

Its abundant, uranium is ubiquitous, cheap and easily stockpiled, and comes already stored. The reactors are well understood known technology, and it transpires that radiation isn't nearly as dangerous as we had been led to believe, and we could easily achieve adequate safety at much lower cost.

But nuclear isn't on the table. Every other permutation of artStudent™ thinking in terms of wacky schemes that were discarded generations ago by sane engineers, are the substance of dinner party chatterati. Hydrogen, carbon capture, Geothermal, tidal, wave, run of river, spinning flywheels, grid scale batteries molten salt tanks (that one might almost work with a nuke to drive it) heat pumps, electric cars. All of this to avoid the basic solution that nuclear power means, at a stroke, you don't need ANY of that crap.

At current electricity wholesale prices, a nuclear fed simple restive heater would be one third the cost of a renewable fed heat pump in terms of electricity, and one tenth the installation cost. Not very efficient, but who cares? uranium is cheap as chips and there's tonnes and tonnes of it around and you don't need very much. E=mC^2 etc etc

In short there is no shortage of cheap energy. Of all the problems society has, lack of cheap energy is not one of them. Only our refusal to embrace it is the problem

That doesn't sort out the use of fossil fuels as chemical feedstocks of course, and as the only appropriate energy density energy source to fly transatlantic airliners, but we will all be locked down anyway, wont we.?

You're certainly right about population. That seems to be such a bad thing to say that its not even whispered about by anybody. Yet, any attempt to prevent global warming is doomed to failure without reductions in both the humam population and in individual (net) resource consumption.

Maybe it can be used, presumably in small factory-produced, reactors similar to those used in submarines, but studies I've seen point out that in terms of global warming, nukes still produce around 30% of the CO2 from conventional thermal generation once mining and refining the stuff is taken into account: Storm van Leeuwen & Smith -

I'n not against nuclear, PROVIDED THAT the problems of disposing of the radioactive waste from fuel preparation and the radioactive debris from decommissioning old plant can be sorted out. To date the solutions have mostly been to pile the junk in a corner and hope nobody notices it.

True enough, do we really need so many transatlantic airliners? Also, I'm seeing talk of running ships on Ammonia rather then heavy oil:

NH3 + O2 => N2 + H2O + energy

Is ammonia's energy content high enough to run an airliner? Gaseous hydrogen's isn't and nor is liquid hydrogen's once to take density/volume/ container mass into account.