Classroom fan automatic controller

At present, the power supply is tight, and it is imperative to save electricity. A variety of power-saving devices have been developed on the market. This article introduces an energy-saving circuit for controlling the operation of classroom fans. According to the requirements, the fan can be designed to automatically run when the temperature reaches 28℃ or above and there are people in the classroom, otherwise the fan cannot be started. Thus, the purpose of saving electricity is achieved.

The circuit is shown in the figure. Power supply circuit: The mains electricity is rectified by VD1~VD4, R7 is used to reduce the voltage and limit the current, and 7806 is used to stabilize the voltage to supply power to each control circuit. Sensing human infrared: When the pyroelectric infrared sensor PIR detects the infrared signal radiated by the human body in the classroom, the 2nd foot of the sensor outputs a weak electrical signal, which is coupled by C1, amplified by the transistor VT, and then input into IC1 A of the operational amplifier 1M324 through C2 and R4. Because IC1 A, R5, R6, C2, R4 and other components form a comparator, when the potential of the 3rd foot is greater than the potential of the 2nd foot, the 1st foot outputs a high level and is sent to the 1st foot of IC2A of the four-2 input NAND gate of IC2 (741S00). Temperature detection circuit: R5, R6, RP1, and Rt form a bridge circuit for detecting temperature changes. Rt is a thermistor with a negative temperature coefficient. By adjusting RP1, when the temperature is equal to or greater than 28°C, the potential of pin 6 of IC1 B is lower than the potential of pin 5, and pin 7 of IC1 B outputs a high level, which is sent to pin 2 of IC2A. Drive and delay: IC2 mainly plays a driving role. For IC2A, under the above conditions, both input terminals are high, so the output is low. After IC2B inverts, it outputs a high level, VD5 is turned on, C3 is charged, and when the potential on C3 rises to a high level. After IC2C and IC2D invert, the high level is output to trigger the thyristor to turn on, and the fan M is powered on and starts running. The role of delay: When the human body is sitting and motionless, IC1A outputs a low level, and IC2B outputs a low level. C3 discharges through RP2. Since RP2 is large, C3 discharges slowly and can maintain a high level for a period of time, so that the thyristor is turned on for a period of time, and the fan continues to run. When the human body moves again, IC2B outputs a high level again, charging C3 again, so as to keep the thyristor triggered and turned on. This ensures that the fan keeps running when the temperature is greater than or equal to 28℃ and there are people in the classroom. When the temperature is lower than 28℃ or no one is in the classroom. The fan cannot start. Although the temperature is greater than or equal to 28℃, the fan automatically stops when people leave the classroom for a period of time (such as 5S, the delay length is set by RP2) to avoid the phenomenon of turning on the fan at low temperature or not turning off the fan after people leave.

R9 and 1ED are used as power indication.

Main components: Device parameters are shown in the figure, R1, R2, R3, select 1/8W, R7, R8 select 1/2W carbon film resistors, R5, R6 select metal film resistors, RP1 selects wirewound potentiometer or metal film potentiometer, PP2 selects glass glaze potentiometer, Rt selects a thermistor with a temperature coefficient of 510kΩ at room temperature, VD1~VD4 select ordinary rectifier diodes, VD5 selects 41 48, IC1 selects 741S00 or CD401 1, IC3 selects 7806, VS selects MCR100-8 plastic-sealed unidirectional thyristor, and pyrolytic infrared sensor selects SD02.