Vermes
Advanced Member level 4
This is a design of thermostat for home made etching machine based on microcontroller Atmega8, digital thermometer DS18B20 and relay JQC-3FF.
Digital thermometer DS18B20 is connected with the microprocessor. Communication between them is implemented via 1-Wire. Pins of the thermometer were protected with heat shrinkable tubing, and the whole was additionally flooded with thermoglue, which prevents the etching from flowing out.
Executive element consists of the relay JQC-3FF with WAGO connector to connect the heater. The relay is controlled by NPN transistor BC 337. Correctly connected LED lights when the heating is enabled.
Seven-segment two digits display with common anode is used in this project. The display shows the current temperature.
Control button is used for changing the set temperature in the range from 30 to 50 degrees Celsius. Pressing the button increases the temperature by 1 degree cyclically until the range is turned back from 50 to 30 degrees Celsius. At the moment of changing, the set temperature is displayed with a dot at the end, so it can be easily differentiated from the current temperature.
Regulation uses simple hysteresis – the heater is turned off at the set temperature, while it is turned on at the temperature which is 3 degrees lower.
The entire device is powered from 9V power supply (stabilizer 7805 decreases the voltage to required). Heat sink operates effectively in this case.
Design of PCB:
PCBs were designed in Eagle. One of them is placed on the front panel with the display, button and diode, while the second is placed in the housing of etching machine with the microcontroller. Both PCBs are one-sided.
Software:
Software was written in VMLAB in C – 1-Wire protocol was implemented. Load can be found in the attachment to the original thread – link below.
Pictures:
Link to original thread (useful attachment) - Termostat do wytrawiarki (Atmega8, DS18B20 - termometr, JQC-3FF - przekaźnik)