Update – 20190826

You always seem to find errors when it's too late for changes :)

• used interrupt pin in the "wrong way":
  • switching it to +Vbat (via 50k, so the high voltage doesn't kill the pin)
  • forgot pull-down resistor

The right way would've been: using the internal pull-up and switching to GND...

• C4 should've been directly tied to the regulators input. It is connected correctly to +VBAT and GND, but not as close as possible to the regulator. As the whole board is only 25x25mm it shouldn't be a problem though...
  

Update – 20190816

Today I finished my square inch design and ordered it at Aisler:

This time I added a stainless stencil for top and bottom because I hate adding solder paste with a toothpick or syringe :)

Intro

For a few of my planned projects I need the board to be quite small. So I made a very basic version. It misses all the nice "usability" features, the bigger board has.

Facts

The cut-off parameters are set once while programming (and can of course be re-programmed) and there are not LEDs to show the state of the board.

Off-current should be well below 10µA, working-current will be around 1mA when measuring, which is around 10% of the time (while not measuring the Attiny shuts down), so let's assume the working current is around 15% of 1mA, so 0.15mA averaged over time...

The board is 25x25mm in size, it will fit into many many tight spots!