Fruit and vegetable greenhouse humidity control circuit

This humidity control circuit is suitable for rough humidity
control in spaces with relatively stable humidity and large volume. It consists of power circuit, humidity measurement circuit and humidity control circuit.
    Humidity measurement circuit: A self-excited multivibrator is composed of transistors VT7 and VT8. The output signal passes through
an AC-DC converter composed of a rectifier bridge VC4, etc., and then the DC microammeter PA (scale changed to humidity) displays the reading.
    Humidity control circuit : It consists of operational amplifier A, Schmidt circuit (VT9, VTio), inverter VTl1, relays
KAi, KAz, electric humidifier EH and fan M, etc.
    When the humidity is lower than the set value, relays KAi and KA2 are closed one after another, and the electric humidifier EH and fan M work.
When the humidity rises to the set value, KAi and KA2 are released, and both EH and M stop working.
    Adjust the potentiometer RPz to change the humidity set value; adjust RP4 to adjust the trigger sensitivity of the Schmidt circuit.