Sensor design for automatic control system for indoor lighting equipment

With the rapid development of the economy and society, electric energy is getting more and more tense, and the phenomenon of wasted energy still exists. In many colleges and universities, there is a problem that classroom lighting management is not in place. At night, the empty classrooms are still brightly lit. For such large buildings, lighting energy saving is becoming more and more important. The widely used lighting energy-saving switches are basically voice-activated, contact-type, etc. Due to the limitations of use, these switches can only be used as an auxiliary part of the control system. To realize the intelligent and energy-saving indoor lighting system, the most important point is that the system can detect and judge the presence of human beings. The passive pyroelectric infrared sensor on the market is limited to detecting dynamic human body and people who are sitting in the classroom. Do not react. The project team designed a low-cost, low-power indoor intelligent control system based on the active pyroelectric infrared sensor.

2. Overall system function and structure

2.1 Features

Pyroelectric infrared technology is used to detect whether there is any person in the room. When someone enters the room, the sensor detects the infrared rays emitted by the human body and generates a current signal. The signal is processed by the integrated processing circuit IC and transmitted to the single-chip microcomputer. The single-chip microcomputer controls the illumination through the control relay. The switch of the device, after which the single-chip computer controls the motor to rotate the sensor at intervals. If there is always a human body in the room, the lighting device remains energized. After the person leaves, the sensor closes the load due to the detection of the human body in the next detection cycle. It can achieve the effect of "people to light, people in the light, people off the light, safe and energy saving".

The intensity of the indoor light is detected by a photoresistor. Using the illumination characteristics of the photoresistor, the current generated by the photoresistor changes with a change in relative light intensity at a certain voltage, and these electrical signals are sent to the single-chip microcomputer, and the switch of the lighting appliance is automatically controlled by the single-chip microcomputer.

In terms of model power consumption, the sensor is up to 5W in the case of rotation and up to 0.5W in the static case. If the sensor is properly arranged in the classroom, energy-saving control of the lighting device can be realized.

2.2 structure block diagram

The design consists of an active pyroelectric infrared sensor detection module, a single-chip control module, an ambient light intensity detection module, and a relay execution module. The structure is shown in Figure 1.

3. System hardware equipment

3.1 Active Pyroelectric Infrared Sensor

Normal human body temperature is 36 ~ 37 ° C, will emit 9 ~ 12μm infrared. The pyroelectric infrared sensor can sense infrared wavelengths of 0.2 to 20 μm, and infrared rays emitted by the human body can be received by the sensor. When the human body produces alternating infrared radiation to focus on the infrared sensing crystal, the crystal surface temperature changes, and the crystal having the pyroelectric effect produces polarization. The reason why the passive sensor does not detect the static human body is that the infrared radiation generated by the static human body does not change in the detection area, the surface temperature of the electrolyte crystal remains unchanged, and no electrical signal can be generated. Only when the infrared rays emitted by the human body alternately change, the surface of the electrolyte crystal The temperature changes accordingly, and the amount of surface charge changes, and an excess floating charge is generated to generate an electrical signal. Based on the above principle, the active pyroelectric sensor is driven by the motor to rotate the front and back alternately according to the relative motion, and forms a relative speed with the static human body, so that the infrared rays emitted by the static human body alternately change at the receiving end, thereby generating current.