There does seem to be an issue with SPIFFS slowing down appending onto large files and ultimately failing. So maybe the thing to do is to have a series of files each capable of holding say 256 records. Indexing would still be pretty straightforward as the high byte of the index would select the file...

Why not use 1 file for all the records to maximise space efficiency?

Decide on your maximum record size.
Block in file is Length (4 bytes) + max size.
Seek to record position (n x (4 + max Size)
Read or write length + data

I think you need to say a little bit more about where you think you need help. Like 1) Hardware interfacing 2) Basic development environment set up 3) Basic software development to set up and periodically read gauge 4) Web development (assuming that is a phone display) or 4) Local display onto scree...

Are you using x10 probes to view these signals? A x1 probe has significant capacitance and could well explain the rise time.

Piggybacking on an existing Alexa integration would work for a personal project but might look 'unprofessional' if you are marketing this a a product. If this didn't worry you then I don't know if there any legal implications. One can use intermediary services like IFTTT but that complicates set up ...

When either DTR,RTS are both high or both low then EN and GPIO0 will both be high. It is done this way to ensure that the chip will run normally under either of these conditions. When DTR is high and RTS is low then GPIO0 is high and EN is low. Similarly when RTS is high and DTR is low then EN is hi...

Little bit more info on the XC6203 LDO regulators. The maximum peak current is 600mA with the sustained output current of 400mA. I use the E series which has no built in current limiter to ensure that doesn't kick in. With a 220uF miniature SMD output capacitor I haven't seen any significant brown o...

I use xc6203 LDO regulators with LIPO batteries. These have a drop out of around 150mV at the normal supply currents and also a fairly low quiescent current of around 8uA to minimise battery drain. As the modules will work happily down to 3.0V this means the batteries are good down to about 3.3V whi...

Difficult to see what is going on as code example seems to be badly formatted onto one line.

It does look like there might be a missing semicolon after the digitalWrite in morseDebug

I think something like this would work. LP3470Reset.jpg Battery includes any charging / protection circuit you are using. When voltage is above 3.6V RST is high, MOSFET turns on and connects circuit ground back to battery ground. Capacitor controls delay on releasing RST after battery goes above 3.6...