Inside a mains socket tester with LCD display. (with schematic)

I was sent this socket tester by Adrian, who had been disappointed that the LCD display was not the information display that was implied in some of the eBay listings.
The LCD display is very simple, but it does provide a very functional test for dangerous voltage potentials with respect to the building's earth/ground circuit. That's rare, but a polarity test is an important part of the test of an electrical installation. This plug is simple, but very functional. It's not as glamorous or sophisticated as the "Socket & See" tester with its automatic loop impedance check (the resistance of the entire live/earth loop to the utility transformer) but it's a fraction of the price.
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