temperature controller circuit

Automatically controlled humidifiers can be used for ambient humidity control in homes, and can also be used for humidity control in incubators or poultry houses in poultry farms. When
the humidity is lower than 50%, can the humidifier work automatically? Maintaining a certain humidity environment is good for the health of both humans and animals.
    (1) Circuit composition The automatic control humidifier circuit consists of a power supply circuit, humidity detection, indication circuit and humidity control circuit, as
shown in the figure. The power circuit consists of power transformer T, rectifier bridge UR1, filter capacitors cl, C2, resistors, and light-emitting diode I. ED
is composed of three-terminal voltage stabilizing integrated circuit ICl (LM7812).
    The humidity detection and indication circuit consists of a power transformer T that steps down 8V, resistors Shu~Shu, Zener diodes VSI and VS2, potentiometer RP1,
humidity-sensitive resistor RS, rectifier bridge UR2, capacitors C3 and C4, and ammeter PA.
    The humidity control circuit is composed of operational amplifier IC2 (FLA741), resistor R-R, diodes VD1 and VD2, transistor VT and relay
K.
    (2) Analysis of the working principle of the circuit. After one channel of the AC 220V voltage is stepped down by T, UR1 rectified, cl filtered and stabilized by 1C1, a
+12V voltage is generated and supplied to the humidity control circuit, and VL is lit at the same time. The other channel is stepped down by T and Ri. And the current limiting and VS1, vsz voltage stabilization and clipping
become a flat-top AC voltage. This AC voltage is adjusted and sampled by RP1, stepped down by RS and rectified by UR2 to become a DC voltage, and then passes through C3 and R.
After filtering with C to limit the current, add it to the ammeter PA. The resistance value of RS changes with the change of humidity. The higher the ambient humidity. The smaller the resistance of RS
, the greater the DC current flowing through the PA.
    When the humidity is low, the current flowing through R is also small. The voltage at the inverting input terminal of IC2 is lower than the reference voltage at the non-inverting input terminal and outputs a high
level, causing VT to turn on. K pulls in, and its normally open contact is connected, allowing the humidifier to be powered on. As the air humidity continues to increase, the resistance of RS
also begins to increase, and the voltage at the inverting input terminal of IC2 also continues to rise. When the humidity reaches a certain humidity, IC2
outputs a low level because the inverting input terminal voltage is higher than its positive input terminal voltage, causing VT to cut off, K to release, and its normally open contact to cut off the humidifier 's working power supply. By working in this way repeatedly
, the ambient humidity can be controlled within the set humidity range.