Vermes
Advanced Member level 4
This is a useful in the implementation of PCBs based on the photochemical method using photosensitive emulsion POSITIV 20.
It is a stove for heating boards, following the application of the emulsion.
The stove speeds up the process of making the ready board, because after 15 minutes of heating in 65 degrees Celsius, the board is ready to be irradiated and digested. Of course, the boards have to dry about 10-15 minutes in room temperature after applying the emulsion.
Microprocessor Atmega8 controls the temperature. Thermocouple K with the system MAX6675 measures the temperature.
The processor also multiplexes the 7-segments LED displays and enables/disables the heaters.
The temperature microprocessor controller was made unusually. Atmega ADC was used, which measures the voltage on the slider of the potentiometer.
Programming the temperature has three degrees. Increment occurs with steps of 1, 2, 5 depending on the deviation of the axis of the potentiometer from the home position. The system is very efficient and resistant to interference, since it operates in specific ranges defined in the program.
To ensure tolerable temperature conditions for the control system, you have to isolate heat chamber from the control chamber. For this purpose, a glass mat approximately 5mm (three layers) with a temperature resistance of 2000 degrees Celsius. The mat was covered with aluminum foil to avoid dust. To ensure the conditions of electrical insulation of thermistor and heaters, there is no foil from the bottom, so everything is in perfect order.
Additionally, it was insulated with aluminum adhesive tape used to connect pipes for heating, fireplaces, etc.
In addition to factory ventilation, you should provide forced air circulation (fan), because metal housing heats up. It may be useful when temperature exceeds 100 degrees Celsius.
Factory protection in the form of thermistor operates at 200 degrees Celsius – the temperature of the stove with two heaters enabled. One heater heats the stove to 180 degrees Celsius, if it is needed.
Heaters can be chosen by an original switch, whose system is a little different from the one placed on the scheme (the original switch allows to enable each heater separately or both at once). Moreover, there is no main switch on the scheme.
Link to original thread (useful attachment) – Piec do suszenia emulsji światłoczułej na pcb