4 Channel Temperature Logger

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.

I finished the user interface software tonight. Screwed the back on the case. There is always something special about being done enough to screw the case together. Now it is time to see what I can see by using it!

People looking at the front of the box may notice a gap between the left end of the LCD and the edge of the window for it. I machined the box early in the morning, before getting my caffeine, and transposed a digit, putting the end of the window at 9.844" instead of 9.484". In general, erasing mistakes in machining is painful. It is possible to weld a patch into that panel, but this box is a tool, not a piece of art...