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IR automatic lighting control. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Lighting

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In order to automatically turn on the light in the room when a person enters there, it is necessary to somehow "feel" his presence. One of the possible signs is the natural radiation of a person in the IR range of the electromagnetic spectrum. Since a person, being in a room, almost never remains motionless, the intensity of the IR irradiation of the sensor is constantly changing, which is the basis of the principle of operation of the proposed machine. The device made by the author has been working flawlessly in the kitchen around the clock for more than a year.

Devices that respond to natural human infrared radiation are often used in indoor security systems. Outwardly, they look like small boxes with convex frosted glass facing the possible appearance of an intruder. Upon closer examination, it can be seen that the "frosted glass" is inhomogeneously divided into segments with different angles of inclination and surface curvature. This is a Fresnel lens, the prototype of which was proposed at the beginning of the XNUMXth century for the equipment of marine navigation beacons. It directs the light of one source into several narrow beams oriented in space in the required way.

IR automatic lighting control

Working "for reception", a similar lens gives the sensitive area of the IR radiation receiver a multi-beam character. As a result, the intensity of the thermal radiation of a moving object (person) focused on the surface of the sensitive element reaches a maximum when it is in one of the beams, and a minimum in the interval between the beams.

IR radiation receivers in such devices are usually pyroelectric sensors - relatively cheap and quite sensitive products that respond only to changes in the radiation intensity. Outwardly, such a sensor is similar to a conventional transistor, in the case of which a window is provided that is transparent to IR rays. It usually contains several sensitive pyroelectric elements connected between the gate of the built-in FET and an external terminal. Two more outputs are the source and drain of the transistor. The location and purpose of the outputs of the RE46 sensor used in the machine described below is shown in fig. 1 (view from the terminal side).

On fig. 2 shows a diagram of a lighting control machine. The amplitude of the useful signal at the load resistor R4 in the drain circuit of sensor B1 reaches 50 mV. A bandpass amplifier is assembled on the op amp DA1.2, and a limiting amplifier is assembled on the DA1.3, which converts the sensor signal into rectangular pulses of constant amplitude. A single vibrator with a restart on the op-amp DA1.4 is necessary to keep the light on in the pauses between pulses, in the time intervals when a person in the room remains motionless, and for some time after he left the room. The exposure time is regulated by a tuning resistor R19.

(click to enlarge)

In the initial state (at a low voltage level at the output of the op-amp DA1.3), the voltage at the output of the op-amp DA1.4 is low, the capacitor C8 is discharged, the transistor VT1 is closed, the relay winding K1 is de-energized, the lighting is off. When a high-level pulse appears at the output of the op-amp DA1.3, the same level will be set at the output of the op-amp DA1.4, which will lead to the opening of the transistor VT1 and the operation of the relay K1, which turns on the lighting.

At the end of the pulse, the VD1 diode will close, but thanks to the capacitor C8, the state of the op-amp DA1.4 will not change. The lighting will remain on while this capacitor is being charged through resistors R18 and R19. Positive pulses at the output of the op-amp DA1.3, appearing before the charging of the capacitor C8, discharge the latter, as a result of which the shutter count starts again.

If there were no pulses for a given time and the voltage at the non-inverting output of the op-amp DA1.4 dropped below that applied to its inverting input, the one-shot will return to its original state by turning off the lighting, and the capacitor C8 will be discharged through the output circuit of the op-amp DA1.4 and diode VD2.

A photorelay is assembled on the DA1.1 op-amp, which reacts to the general illumination of the room. Its sensor is a photoresistor R2. It is necessary that artificial lighting turns on automatically only when there is insufficient natural light, and not every time a person enters the room (even in the daytime).

In high light, the resistance of the photoresistor is small and the voltage at the inverting input of the op-amp DA1 1 exceeds the threshold set at its non-inverting input using a tuned resistor R7. The voltage level at the output of the op-amp is low. Acting through the resistor R12 to the input of the op-amp DA1.3, it keeps the machine in a state corresponding to the off lighting, regardless of the IR signals received by the pyroelectric sensor B1.

With decreasing illumination, the resistance of the photoresistor increases, the voltage at the input of the op-amp decreases, and as soon as it drops below the threshold, the state of the op-amp DA1.1 will change, removing the lock from the sensor. When a signal to turn on artificial lighting is given, a high voltage level at the lower output of the resistor R8 according to the circuit (it is connected to the output of the op-amp DA1.4) leads to a significant increase in the photorelay threshold, actually turning it off.

The machine can be powered from any source of constant voltage 10 ... 16 V. The current consumption does not exceed 10 mA in standby mode, and when triggered, it increases by the value consumed by relay K1.

The device is assembled by surface mounting on a fiberglass board placed in a housing from a security signaling device ("motion sensor"). The pyroelectric sensor RE46 and the Fresnel lens CE12 were taken from the same signaling device, forming a 24-beam sensitive zone extending over a distance of 1,5 ... 5 m of the sensor. The mutual position of the sensor and the lens, which was available in the original design, must be preserved. Instead of a Fresnel lens, you can install a flat or convex frosted organic glass of a suitable size. However, the detection range of a moving person will decrease.

When soldering the leads of a pyroelectric sensor, it is necessary to avoid overheating it and take precautions to prevent damage to the device by static electricity charges. Often, a damaged sensor loses sensitivity significantly without losing its functionality completely.

Relay K1 - automotive 3747.06, it can be replaced by another with a response voltage of 8 ... 11 V and contacts capable of switching a current of at least 2 A at a voltage of 220 V, for example, BV2091-112DM (Pasi).

The device is installed in such a way that a person entering the room and moving in it crosses the maximum number of rays of the sensitive zone. Usually, the optimal position can be found experimentally in several attempts. The adjustment of the machine is reduced to setting the desired delay for turning off the light with resistor R19, and the threshold for operating the photorelay with resistor R7.

False positives are inherent in all such devices, the probability of which can be reduced, but cannot be completely eliminated. Insects crawling on the surface of the lens, or spiders weaving a web in the immediate vicinity of it, are often the cause of the operation. Therefore, the installation site of the device must be kept clean and periodically sprayed with insecticides.

It is undesirable that in the sensitive area there are powerful sources of IR radiation, for example, heating and other household appliances that emit a lot of heat during operation. The sensitive surface of the sensor must be protected from direct sunlight.

Author: A.Kashkarov, St. Petersburg

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