https://pandao.github.io/editor.md/en.html
The utility frequency, (power) line frequency is 50Hz
1 period = 1/50
1 period = 0.02 s
0.02s = 20,000 μs
therefore, if we insert antennas into digital pin 2 and analog pin a0,
we will get a meander with a frequency of 50 Hz and a period of 20 000 μs
Attach signal source between digital pin 2 and gnd, read output
Attach signal source between digital pin 2,digital pin 3 and gnd, read output (2 strings)
