oh it’s an optical interface to a smart meter, not “optical meter”. Could not find the schematic or BoM for the $15 PiggyMeter board. How does this “set new standards for documentation”?

[mircemk] had previously built a frequency counter using an Arduino, with a useful range up to 6 MHz. Now, they’ve implemented a new design on a far more powerful STM32 chip that boosts the m… ...

This simple micro ampere meter circuit can help in measuring small currents in five ranges: from 1 µA to 10 mA. The meter is working in this way: the current being measured Ix shifts the input voltage ...