Additional information and documents of the old project presented in 2013

The article published in 2013 was incomplete and lacked enough information for the use of interested parties, so in this supplementary article, an attempt has been made to provide sufficient information.

Instead of U1, you can use any type of low-consumption CMOS op-amp, such as "TS271N" from ST.
In this case, according to the data sheet, the resistor (R4) should be replaced with a value of about 4.7 to 8.2 Mega OHM.