So perhaps they are counterfeit chips, which are simply pin & code compatible? I also found rumors about “ghost” shifts, where legitimate manufacturer plants/equipment are used off the clock to produce extra parts. While I waited for them to ship on the proverbial slow boat, I did some digging, because these modules were (almost) selling for less than the chip itself if I bought them directly from trusted sources like Digikey, Mouser, etc.
and I eventually bought a couple to try them out. I built the first few beta units with the DS3231 Chronodot from Macetech ( about $18 each), but I kept on stumbling across cheap RTC modules on eBay, Amazon, etc. So you could say that the most important sensor on the unit is the real-time clock (RTC), who’s alarm signal wakes the sleeping processor and begins the cascade of sensor readings. Since the Cave Pearl is a data logger, it spends most of the time sleeping to conserve power.
NOTE: There is now an M variant of this chip on the market which is more resistant to vibration, but the -M is only temperature compensated to ±5ppm. A ☒ppm DS3231N for less than $1? Really? And most of these boards use the industrial SN variant, which is rated for the full -40☌ to +85☌ temp range.
