Very happy to have just received the PCBs for the next iteration of this temperature logger, the NestProbe TL2.

In an effort to reduce cost and complexity, I spent much of past autumn designing a new model of the temperature logger. Thanks to Jan who pointed out details about sensor accuracy, I also changed the temperature sensor to Silicon Labs' Si7051, which is more expensive but more accurate and NIST-traceable.

Main changes for this iteration are:

• Changed MCU to ATtiny816. The 328PB was great but a bit too much for such a simple application. The ATtiny is also almost half the cost, at just over 50 cents per unit, and it also has half the current consumption when in ultra-low-power.
• Changed temperature sensor to the Si7051. It is slightly more expensive than the MAX30205 but it's meant to be more accurate and has a NIST-traceable certificate. Let's see!
• Changed all passive components from 0201 to 0402. I had used 0201s for the TL1 because I was trying to break all MCU pins out to optional headers. With traces for 28 pins, I needed the space. That proved to be too difficult to solder with even the slightest problems in solder paste quality or concentration, and once I had problems in the first go it was too difficult to fix. The 0402s should make home-manufacturing much less painful.
• Fewer breakouts. I've traced five pins to a set of headers but I'm hoping in later prototypes to still break-out the rest of them. Especially I2C and SPI to allow additional sensors and connection to a LoRa module.

I'm looking forward to put this on the frying pan and start coding!