ThomasSTM8S003F3P6 µCs are cheap (OK, this isn't the first time you read that). Some time ago @K.C. Lee used off-the-shelf TSSOP adapter PCBs as a simple µC board. A great idea! Like that one can make a Li coin battery powered board for about $0.60:
| Component | @ | $/unit |
| STM8S003F3P6 | 10 | 0.24 |
| PCB SOP/TSSOP/DIL20 | 10 | 0.11 |
| 2x 1uF ceramics capacitor | 100 | 0.02 |
| CR2025 | 10 | 0.13 |
| Li battery holder | 10 | 0.10 |
Like K.C. I added the essential components (2x 1µF capacitors) to the unused SOP20 pads on the other side, and did a test with the SWIMCOM image, and it worked nicely!
In "active halt" state it can run quite some time as an environmental data logger. I have some ideas for low-bandwidth environmental sensors that can be deployed, and recovered later on. I'll call this a "sensor throwie", since it's not a bit loss if some of them can't be recovered (missing in action. so to say).
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STM8S brown out detector has a 2.8V (max) threshold. This doesn't give a lot of head room. You should use a larger decoupling cap as those Li coin cells have high internal resistance.
Those super glue bottle caps can be used for housing these PCB if you round off the corners a bit. A piezo disc also fits.
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You're right, the brown out detector is the limiting factor, and cheap STM8L0x devices aren't available on the hobby market. Turning to STM32F030 might be an option (1.8 .. 3.6V). I've also been thinking about a self-boosting circuit using the brown-out detector as a comparator (with NRST as the output). This just might be crazy enough to work ;-)
Good idea to look in the garbage for throwie housing. I guess I will have to look for different items, though. Garbage is different over here.
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You would want the brownout detector as a bootstrap until you can bring a timer peripheral online.
Medicine caps, large bottle caps etc.
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hah, that'd be a hack-and-a-half!
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