Automatic thermostat

Shown is an automatic thermostat controller , which can perform constant temperature control on thermostatic boxes, thermostat furnaces, etc. The circuit
is mainly composed of temperature detection, voltage comparator, etc.
    The 220V AC power supply is stepped down by C3, rectified by the full-bridge BR, and filtered and stabilized by C2 and VD to obtain a +12V DC power supply
for circuit operation. RT, I and LM358 form a temperature detection circuit. RT is a positive temperature coefficient thermistor. By adjusting RP,
you can adjust the starting control point of the temperature. For example, assuming the temperature is controlled below 45°C, first set RT to 45°C. of hot water
, carefully adjust the RPi until the LM358 outputs a high level . When the temperature is lower than 45°C, the resistance value of RT is small, the potential
of the (one) terminal of LM358 is higher than the potential of the (+) terminal, the output is low level, the transistor VT and the thyristor vs are both turned on, and
the heating resistance wire RL is heated; As the temperature increases during heating, the resistance value of RT begins to increase, and the potential of terminal (1) gradually decreases. When the potential of terminal (1) is lower than the potential
of terminal (+) , the output is high level , and VT and thyristor vs are cut off. , heating stops . The function of digging is to produce a certain hysteresis in the output, so that the input and output change within a small range such as 45±0.5°C centered on the control point . The size of the change range is determined by R.