When I built this project back in 2018, I used a CPU board left over from another project. That board has a WIFI module on it that was not being used at all here. That particular module has been discontinued by ST (Boo ST) and I have a lot of software developed for that module. In the interest of using that module for another project so that I don't have to write more code for a different module, I designed a replacement CPU board that has the same processor, clock chip and NVM chip as the original board. The bare boards arrived from OSHPark, and I built it this morning. The new board powered up and operates fine. I swapped the boards and connected the thermocouple boards to the new one and all looks good.

One plus of the new board is that it is about 1/3 smaller than the WIFI version, so it is a less expensive board. The new board is the same width as the original, so two of the bolt holes still line up. As this temp logger is not a rugged environment project and the CPU board is pretty light weight, two bolt mounting seems sufficient now.

When I did the design on the new CPU board, I just removed the WIFI module and it's voltage regulator and brought the now unused I/O out to connectors. I juggled parts around a little bit and was able to reduce the length of the board about an inch. Looking at the finished board, it had a lot of unused space on it. By modifying the power supply design some, moving the clock battery to the back side of the board, and juggling stuff around more, I got about 25% more out of the board area. A number of my projects need some non-volatile memory, and an external hardware clock is a nice option, if slightly expensive. There are two unbuilt boards for the replacement CPU. When they get used up, I will send out the size reduced version of the PCB for fabrication.