In my thesis, I designed a tester device for an MCU board what is part of the "access control and time & attendance system'" which was developed by the Leviathan Solutions Elektronikai és Fejlesztő Kft. A function of the MCU board is to process the data which is given by the cardreaders at the doors, and to response appropriately for the permissions. For example open the door or switch the indicator relay. The object of the tester is to connect to the inputs and outputs of the MCU board; check for short circuit and verify the proper functionality. The product family includes a power panel too. During the calibration of the power panel, we have to give different voltages to the power board. The tester has to make automated this process. In the thesis, I designed the schematic and the pcb of the tester and developed the firmware for it. The firmware should be able to receive commands and datas through ethernet connection and accordingly run the tests. The test can be short circuit test, power board calibration or even generate testdata, so the tester can verify the right answer from the MCU board.