Thank you for your interest.
«I am missing units of measure in the graphs» - You are right. I didn't put the units of measurement in the graphs. I described the graphs in the beginning of every paragraph.
«Why is there a significant dip at 50?» - every sensor has its own transient response. Some pyroelectric detectors are faster, some not. Serial opposed dual pyroelectric detectors have transient responses longer than parallel. I found value 50s to be approximately good for all of the samples. Also, this value is comparable with the scale of percentage, so 100s, or 100%, is the length of the full period, and 50s, or 50%, if that of one of the two transient responses, heating or cooling respectively.
«Maybe overlaying the sensors in one graph per category would allow for a quick comparison of the response.» - every graph includes four lines. If I overlay all of them one another, I'm afraid, we will receive chaos. I think It would be a good idea to overlay the approximations only. What are you thinking?
«A summary/conclusion would also be helpful to the reader.» - You are right twice. But I didn“t do it for the next reasons.
This method is too young, the first attempt. I don't have enough knowledge, skills or practical experience do write conclusion. When a half of the year have passed by, I will, probably, be able to write good, professional conclusions.
As the author, I am also interested in the opinion/conclusions of the other people. This is why I have posted it here.
If you have more questions, please, feel free to ask. If you know the other people interesting in pyroelectric measurements, invite them to this discussion. This topic is brand new. I am looking for more feedbacks and opinions. I'll be glad to receive positive, but also accept critics. The truth is born in discussions.
Kind regards in return.
P.S. you can even think about carrying out the same measurements all by yourself. If you find a way how to test motion sensors to avoid false alarms, you will be able to earn something.
@skywatch You are referring to the snippet that combines sleep on timer with pin change interrupts?
I just pasted that code in two randomly picked MySensor example sketches (UVSensor and ClearEepromConfig) and it compiled just fine (MySensors 2.3.2 and IDE 1.8.13). What kind of error do you get?
Edit: If it complains about getSleepRemaining() not being declared, you may be using an older MySensors version. I think it has been added with 2.3.2
Remembering now, the undervoltage and overvoltage protection could both be put under the MCU's control, in which case you could get by with just a diode, or equivalent. It wouldn't be as failsafe in the sense that an unforeseen bug in your code might defeat it, but it could be done. In the end, I'm not sure that the chance of encountering a failure in software is necessarily any higher than that of encountering a failure due to defective hardware.
Alternatively, you could put two cells in series, and in principle that would eliminate any chance of overcharging. With that configuration, if you used a 5v solar panel instead of a 6v, then you'd also eliminate any chance of burning out the atmega328p and wouldn't need extra hardware to ensure against that.
For that matter, you could stick with one cell and just use a 3.5v solar panel. With just that one stroke you wouldn't need anything extra to guard against overcharging the battery or over-volting the atmega328p.
That's what makes embedding solar such a fun problem--depending on the use case, there are such a large number of different ways to solve it. So many that the real game is in comparing the trade-offs.