I came across a circuit scheme that seemed easy to build but it was intended to be used with 8Bit A/D converter (original article).
This converter is used with parallel (LPT) port which can’t be found on modern computers.
Also the 8Bit converter offers only poor resolution of 256 levels of energy and it is hard to calibrate.
The original cuircuit consists of 3 sections, Detector, Converter & power supply.
And I decided to make it alot more accurate and a lot more easy to build.