In this non-contact AC voltage detector, I understand the working principle of taking a tiny induced current in the antenna and amplifying it using transistors. However, I do not understand why the resistors have been used and why the particular values have been selected.
My understanding is that a transistor will give a DC current gain based upon the particular transistor used of say 100. So why has the 1 MegaOhm resistor been used? Surely your induced current will be so small you want to maximise the gain of that signal? I'm just struggling to understand why the resistors have been used.