Hammond-boxed sensor board with STM32 L0x1

The next step after L0x1 development board: STM32L0x1-based sensor board. Same schematic, but on a PCB which matches Hammond 1551GBK box, with a CR2032 battery holder.


The development board was working satisfactorily, so I decided to try to make an "easily deployable" version. I found that it's tricky for me to find the right "project box" for sensors (usually size, then they don't fit exactly so I need to pad them, then the ebay seller disappears and I can't find another one with the same size...) So this time around I went for one of Hammond boxes: they supply datasheets with exact measurements and drawings of the boxes, they're high quality and not that expensive, and one can reliably buy the correct type. The type used here is 1551G (then two letter indicating the colour, so 1551GBK (black) or 1551GGY (gray)), the outer size is 50x35x20mm. The PCB fits perfectly inside, and can be attached through the two mounting holes.


It's based on essentially the same schematic as the development board, with a few more power options. I'll describe the various components of the design separately:

You can get PCBs from OSH Park - I recommend going for the 0.8mm thick ones: they're very cool, and there's more space in the box :)


I use mecrisp stellaris. Starting from jcw's embello, I have some forth words here. (Jean-Claude Wippler wrote up about getting the power consumption as low as possible in a blog post. It's for jeenode zero, but applies also for L041.)

UPDATE 2019-07-24: A boxed board with SHT31-D temperature and humidity sensor is now reporting the data from the outside. The forth code is here. It runs on a CR2032 coin cell battery, and takes 2.5uA in sleep. That's pretty sweet; I originally wanted to use 2 AA batteries, but with the consumption this low it's not worth it. I'll see how it holds up.