Nowadays in some cases there is quite cheaper and easier to buy a complete development board, than buy a single chip. Meantime I remember contrariwise setup with local shops and without 2-week delivery parcel terminals. So, when I have to repair my TV, I decided to build my own transistortester clone instead of buying one on ali.

Just clone of well known transistor tester. The display is old symbolic variant, but the board is nowaday one. All parts are replaced to the SMD ones. Power supply includes TP4056 li-ion battery charger and 5V ME2108 DC-DC stabilizer of instrument power. Very compact ME2139 DC-DC for up to 21V zener or LED testing also included. As well newer Atmega328PB instead of previous Atmega328P is used. It adds 4 additional GPIOS (PE0-3), I applied it for encoder, frequency counter and zener DC-DC switching on-off. So, in this variant there isn't any ports, coupled for two functions, and DC-DC do not discharges the battery, when it is not used.