Use P228 to make infrared remote control energy-saving lighting lamps

The core device of the circuit is a pyroelectric infrared sensor BH. When it senses the trace amount of infrared rays emitted by the human body,
the components in the sensor will clearly feel the change process of its relative temperature. As a strong dielectric, the self-polarization value of the thermoelectric element
is Changes will occur, charge depletion will occur on the surface of the component, and there will be an electrical signal change on the parallel gate resistor Rg + through the matching of the field effect transistor (FET) set inside the BH, an electrical pulse
of a certain amplitude can be output , its pulse frequency is generally between 0.5 ~ 1Hz (this is the most sensitive frequency of BH), and is coupled to the preamplifier VTI through the capacitor Cl for preamplification. The preamplified signal is output from its collector, directly coupled to pin 3 of the operational amplifier Al, amplified with low noise and high gain, and then output from pin 6 of Al. A3 operational amplifier forms a voltage comparator, and RP1 is a reference voltage divider. When the output voltage of pin 6 of Al is higher than the reference voltage of A3, A3 outputs an amplified high-level pulse, and R6 current limits the transistor VT2 to conduct Pass. The conduction of V r2 causes the monostable flip-flop composed of the time base integrated circuit A4 to flip and set, pin 3 of A4 outputs high level, the thyristor vs is turned on, and the lamp H lights up. The transient time of the monostable trigger is determined by R8 and c7, and the data shown in the figure is about 11Os. Therefore, if someone keeps moving in front of the sensor BH, the light will continue to light up; when the person leaves, the light H will automatically go out for about 110 seconds.     Photoresistor RO, transistor VT3 and potentiometer RP2 form a light control circuit, whose function is to make the circuit inactive during the day . Because RG has low resistance when exposed to light during the day, VT3 is turned on, and its saturation voltage drop is only about 0.3V, so pin 4 of the forced reset terminal of A4 is low level, and the time base circuit is forced to reset. Pin 3 always outputs low level, so the lamp will not be lit during the day. At night, RO has no light exposure and shows high resistance. VT3 is cut off to release the blockade of A4, so the circuit can work normally. Potentiometer RP2 is used to adjust the light control value so that VT3 can be turned on or off under appropriate light.     Capacitors C2 and C5 form a low-pass filter to eliminate interference pulses . Rt is a positive temperature coefficient thermistor. Since the sensor BH is sensitive to relative heat, the higher temperature in summer will cause the difference between human body heat (constant) and temperature (variable ) to be significantly reduced. The sensitivity of BH decreases. The resistance characteristic of the positive temperature coefficient sensitive resistor is that its resistance value increases as the temperature increases, resulting in a decrease in the feedback amount of the amplifier, which relatively increases the amplification gain of the operational amplifier, thus compensating for the decrease in sensitivity of the BH due to the rise in temperature. Defects.     The power supply of the whole machine is supplied by the capacitor C11 to step down the voltage and the diodes VD2~VD5 for bridge rectification. The latter circuit is stably supplied by the voltage regulator tube VD1. The front-stage circuit, the sensor BH, is supplied by the three-terminal voltage regulator A2. Its purpose It is to prevent malfunctions that may be caused by power supply voltage fluctuations to improve the reliability of the circuit.