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Presented here design is a useful item in every electronic lab.
Development board is a control unit of this device. The PCB includes processor Atmega16 and some useful peripherals. Solution is heated up by two heaters: 20W and 80W. They are controlled by triacs BT136 supported by optotriacs MOC3043 according to the schematic shown below:
Movement of solution is provided by car washer pump. This construction does not use aquarium aerator which if often applied in such designs, because this would increase the evaporation of a solution of copper persulfate.
The pump is controlled by modulation of the pulse width from transistor N-MOSFET IRF3205, controlled by a discrete driver on the development board.
Control over heaters is carried out via regulator, the so-called Fuzzy Logic. Input data is the temperature measured by DS18B20. The u(T) function has this shape:
The microcontorller carries out the fuzzification, interference and defuzzification. It also includes the rule base. Since the time constant of the process is relatively high, Atmega has enough time for calculations. The picture below presents the temperature versus time after switching on the etching tank:
The device can be controlled by microcontroller Atmega8 and not by development board, because presented here design is only a prototype version. You can also design a housing.
Link to original thread (useful attachment) - Prototypowa wytrawiarka z regulatorem Fuzzy Logic