Rick's b.log - entry 2025/02/08

ESP32 SDK craziness

But that's okay, while I can't develop on this device, it did permit me to extract the apk file from the app installation, to then rename it as .zip, and to look inside. What caught my interest was a bunch of music files within the /res/raw subdirectory of the app.

MP3 files? In a code editor? Who's dumb enough to fall for that?

Upon extracting that, we can see that the provided ESP32 Arduino IDE is version 1.0.3 which is ancient.

That being said, it appears as if ArduinoDroid has been abandoned, last updated nearly five years ago and, I believe, no longer compatible with Android 14. It's a shame as while it does have bugs, it works and it's pretty fast and there's nothing else that offers the same. Plus the adverts aren't intrusive like in some apps so you can actually get some work done. Better yet, it's all local so you aren't tied to needing to access some random cloud service.

The problem isn't just that the provided Arduino IDE is ancient, the problem is also that there's a lot of stuff on the internet that contradicts other stuff. So here are some random lessons learned along the way.

Using SPIFFS

This little filing system is far better for using with the internal SPI Flash than something like FAT. For starters, it is far simpler so doesn't have the overheads and wastage of the FAT structure; but perhaps the most important is that it supports wear levelling to make best use of your flash rather than overwriting the same bits as FAT would.
Note that SPIFFS is deprecated these days as it gets buggy with files over 2MB, but for small files it's fine. The alternative is "LittleFS" and I believe it's a drop-in replacement (replace "SPIFFS" with "LittleFS") but I have not tested this.

You can find tutorials of how to list files in the partition, and maybe even some telling you how to read and write strings of text to a file, but if it's a data block, well...

Using SPIFFS:
Put these at the top, in this order:

   #include <FS.h>
   #include <SPIFFS.h>

Mounting an SPIFFS partition:

   if ( !SPIFFS.begin(true) )
   {
      // do whatever on mount FAILURE
    }

If you pass 'true' to the begin function, it will format the SPIFFS partition for use if mounting fails. If you just do .begin() then this won't be automatically done.

Opening and reading binary data from a file:

   File fp;

   // Open for READING
   fp = SPIFFS.open("/filename.ext", "rb");
   if ( fp )
   {
      fp.read( (byte *)&myarray, sizeof(myarray) );
      fp.close();     
   }

The read method takes a pointer to an array and the array size (in bytes) to load it in.
If this fails with something like "error: no matching function for call to 'fs::File::read(blah-de-blah)" then ensure that you are correctly casting the array as a sequence of bytes using (byte *) prior to the array pointer.
I did find a tutorial that mentioned readBytes, but that didn't seem to want to work for me. It's probably an alias for the read method anyway...

For writing to a file, it's exactly the same but using the write method. Note, also, that the open method is "wb" instead of "rb" this time. That's "w" for write and "b" for binary. Just like fopen() in C's standard library.

   File fp;

   // Open for WRITING
   fp = SPIFFS.open("/filename.ext", "wb");
   if ( fp )
   {
      fp.write( (byte *)&myarray, sizeof(myarray) );
      fp.close();     
   }

I understand that SPIFFS is itself a flat filesystem. Paths begin with "/" because that's just expected, but don't expect to be able to support stuff in directories. It isn't FAT...
Additionally, as this is something from the Unixy world, it's annoyingly case sensitive.

Some device specific functions

   #include "Esp.h"

Then, to do something like force the device to restart, simply call the appropriate function:

   ESP.restart();

Generally, library functions/methods are named such that the first word is in lowercase and all subsequent words have an initial capital, like ESP.getCpuFrequencyMhz(). This looks really weird to me, but at least it's not that god-awful szHungarian bNotation fThat wBlighted szVisualBasic.

Getting time from NTP server

Until it has a time, it'll return the 1^st of January 1970 (when time starts), so you may want to do something like this:

   while ( year < 2025 )
   {
      time(&now);
      localtime_r(&now, &tm);
      year = tm.tm_year + 1900;
      delay(25);
   }

It may be that my SDK here is ancient, but the values don't seem to 'stick', the next call to time() might return 1970, so best to drop this into a get-the-time function.

To get the correct time, you'll need to set up your timezone. To do this, you'll need this code somewhere at the start, prior to enquiring the time.

   // assumes you did #include "time.h" at the top
   configTime(0, 0, "fr.pool.ntp.org");
   setenv("TZ", "CET-1CEST,M3.5.0,M10.5.0/3", 1);
   // use "GMT0BST,M3.5.0/1,M10.5.0" for the UK
   tzset();

This specifies the NTP server "fr.pool.ntp.org" (as I live in France; for the UK it would be "uk.pool.ntp.org").
You may read that it's possible to simply set the UTC offsets in the configTime() function. DO NOT DO THIS. While the string given to setenv() may look like gibberish, it provides the appropriate times of when to change to/from daylight savings. If you don't do this, it'll switch at the times appropriate for the United States.
You can find the appropriate string for your timezone.

Webserver URI parameters

   server.on("/", handle_root);

But how do you deal with parameters given in the URI?

   void handle_root()
   {
      String argn;
      String argp;
      int   argc;

      // How many arguments
      argc = server.args();

      // If there is at least one, read the first
      if ( argc > 0 )
      {
         argn = server.argName(0);
         argp = server.arg(0);
      }

      // rest of the code to output
      // something to the client
   }

If you called, say, http://192.168.1.123/?this=that then argc would be 1, argn would be "this", and argp would be "that".

The letterbox gizmo

Koding in the Citchen.

I think the software is more or less complete now. The harder part is going to be fitting the switches inside the letterbox itself. I might, for a quick hack to see if it works, put them in place using hot-melt glue. It's a bit icky, but a lot less hassle than drilling into metal and trying to work out how/where to make brackets to hold things in the right place(s).
But it's like 3½°C and chucking it down, so... very much not today.

Putting switches in here is going to be the tricky part.

Linky weirdness

So here is the Linky's screen showing that I'm subscribed to 9kW (or 9kVA as it's all Volt-Amps these days because that's a more accurate reflection of power consumption).

What I'm paying for.

And here is the meter telling me it'll trip out at 9000VA. There is apparently a margin of around 10-20% (because volts and stuff), though I haven't tested this nor do I particularly want to.

What I'm supposed to get.

And here, yesterday, was an abnormally high consumption. The car is charging, the water heater was on for a bath, and I flicked the kettle on for a well-needed cuppa.

Might not seem like much, but that would be £2 per hour.

Do you see that little icon? The sort-of-mountain one? That technically warns of over-consumption, and it appears when I go over around 6,000. Push too far, the meter will trip out (and I'll need to reset it manually).
Why? Why is this appearing at six instead of nine?

Note: I'm old fashioned. I think in kilowatts. I will mention kW in the following text, however the meter displays VA. For most intents and purposes, just think that a VA is the same as a watt. The hows-and-whys of where they differ (watts are real power, VA is apparent power) gets complicated quickly (like power factors of resistive and inductive loads), so just assume they're the same thing and handwave the technical stuff, okay? ☺

I just did a test. Turning on various appliances in the kitchen to get around about 3kW on each set of sockets (they're rated 3,680W, or 16A × 230V) gave me around 5.8kW consumption, with the icon showing. I then flicked on the water heater and the consumption hit an all-time high (for me) of just under seven and a half kilowatt. So, clearly my Linky wasn't going to trip out for going over 6kW.
Actually, I fiddled turning stuff on and off and it seems to appear over about 5.5kW. So I think maybe this icon might actually be warning of an unusually high consumption rather than "Danger, Will Robinson, Danger!".
This could be calculated by remembering and averaging consumption over the past whatever duration, or it could simply be something as basic as flagging up if one is over 65% of their rated tariff.

Keep this for posterity - probably the most I'll ever draw.

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