Humidity controller made with CD4011

This circuit can detect the ambient humidity and keep the ambient humidity within the required range by controlling the humidification and drying equipment.

The circuit principle is shown in the figure below.

After 220V AC mains is stepped down by T, rectified by VD1~VD4, filtered by C1 and C2, and stabilized by IC1, a 9V DC voltage is obtained to power the circuit, and VL3 is the power indicator. An oscillating circuit is formed by IC1, R1, R2 and C3 to generate a pulse signal with a frequency of about 2.5KHz. After the signal is divided by RP1, RS and rectified by VD5, it is added to the base of V3 through R3. When the humidity changes, it will cause the change of RS resistance. When the humidity decreases, the RS resistance increases, causing the base potential of V3 to rise and turn on, thereby turning on V1 and V2, V4 off, and relay KA1 energizes to drive the humidification equipment to work, and the humidification indicator VL1 lights up; when the humidity increases, the RS resistance decreases, causing the base potential of V3 to drop and turn off, thereby turning on V4, V1 off, and relay KA2 energizes to drive the drying equipment to work, and the drying indicator VL2 lights up.

This ensures that the ambient humidity is controlled at the set value. The ambient humidity is set by RP1. At the same time, by adjusting RP2 and RP3, the working sensitivity of V1, V2 and V3 can be adjusted.

2. Selection of components

IC1 uses CD4011 2-input four-NAND gate integrated circuit. Other models include CC4011, MC14011, etc. Other NAND gate circuits with the same function can also be used; IC2 is a three-terminal integrated voltage regulator 7809, and models such as LM7809 and CW7809 can be selected; RS uses a universal humidity sensor, which requires that when the humidity is 30%, its resistance is about 10MΩ; when the humidity is 50%, its resistance is less than 200KΩ; when the humidity is 90%, its resistance is about 10KΩ. Transistors V1 and V4 use NPN transistors 8050, and domestic transistors such as 9013 or 3DG12 can also be used; V3 uses 9014, or 3DG6; V2 uses 9012, or 3CG21. VD1~VD4 use rectifier diodes 1N4007; VD5 uses 2AP9 or 2AP10 germanium diodes; VL1~VL3 use ordinary light-emitting diodes. Resistors R1~R6 use 1/4W metal film or carbon film resistors.

RP1~RP3 use organic solid core potentiometers. C1 and C2 use aluminum electrolytic capacitors with a withstand voltage of 16V; C3 uses a ceramic capacitor. KA1 and KA2 use micro relays with a coil voltage of 6V, and the contact capacity is determined according to the power of the humidification and drying equipment.

3. Production and debugging methods

After the circuit is installed, start the humidification equipment. When the humidity reaches the upper limit, adjust RP1 and RP3 to stop the humidification equipment. When the humidity drops to the lower limit, adjust RP2 to start the drying equipment. Repeatedly adjust the above potentiometers to make the equipment work reliably without generating critical oscillations. This means that the debugging is complete.