Leds abbreviation LED, adopt gaas, gallium aluminum arsenic, and phosphating gallium etc material to make, its internal structure for a PN junction, has unilateral electrical conductivity. 

When light emitting diode PN junction, add forward voltage potential barrier PN junction reduced, carriers diffusion movement, cause greater than drift movement of hole injection to N P, N the electronic area is injected into the P area, so the injection of cavitation and mutual electronic met can produce complex, compound produced when the energy of the light's form, and therefore and shine.

Leds in production, use the material differs somewhat, then can issue a different color of light. Light-emitting diodes emitting light colors: red light, yellow light, green light, infrared light, etc. Light-emitting diodes appearance has: circle, square, triangle, rectangle, combined form, special shape and (can also be designed according to customer requirements other form). Common light-emitting diodes (leds) applied circuit has 4 kinds, namely dc, ac drive circuit drive circuit, pulse drive circuit, allochroic luminous drive circuit. 

Use LED for instructions circuit, should meet current limiting resistor string, the resistance of the resistance size should according to different use voltage and LED the work needed current will choose.

Infrared tubes also called infrared emission diode, belongs to the diode classes. It can be directly convert energy near infrared (not visible) and can radiate out light-emitting device, mainly applied in all kinds of photoelectric switch and the radio transmission circuit. Infrared ray tube structure, principle and ordinary light emitting diode similar, but use of semiconductor material is different. Infrared red hair diode usually use GaAs (GaAs), arsenic aluminum, gallium (GaAlAs) and other materials, adopt the whole transparent or light blue, black resin encapsulation.

Infrared receiver head (also called infrared receiver module, IRM) is integrated infrared receiver PD diode, amplification, filter and comparator output of the IC modules.

Infrared receiver head classification can usually divided into 36,37.9, according to the frequency 40,56.7 Khz can choose according to different needs using different frequency.

Infrared sensor, widely used in home of TV, DVD are no longer manufacture receiving amplifier circuit, so that the infrared sensor simplifies the circuit. A common infrared receiving head shape, all have three pins, namely the power supply is VDD, power negative (GND) and data output (Out). Receiving head of pins arrangement for different and different models for receiving head shape, the difference between different and pins.

photoelectric smoke emission & receiver

Photoelectric smoke alarm within an optical maze,installation of infrared tube, an infrared receiving tubedoes not receive the infrared emission tube emits infraredsmokeless, when dust enters the optical labyrinth, byrefraction, reflection, receiving tube receives the infrared light, intelligent alarm circuit judge is not more than the threshold, if more than a warning.

Photoelectric smoke detector can be divided into thereduced light type and light scattering type, as follows:

(1) dimming photoelectric smoke detector

The detection chamber of the detector is provided with a light emitting device and a light receiving device. Under normal circumstances, a certain amount of light receivedby the light device, light emitting device sends out; and in the smoke, light emitting device emit light into theocclusion by the smoke, the light receiving device receives the decrease of light quantity, light current decreases, the detector sends out the alarm signal.

(2) a light scattering type photoelectric smoke detector

The detection chamber of the detector is also provided with a light emitting device and a light receiving device.Under normal circumstances, light receiving device isunable to receive the light emitted from the light emitting device, and thus do not generate photocurrent. In case of fire, when the smoke into the testing room, the smoke particle effects, generate diffuse so that light emitting device emits light, the diffuse light is affected by lightdevice is received, so that by the impedance of the opticaldevice changes,photocurrent is generated, thus realizing the smoke signal into electrical signal function, receivedsignal detector and then determine whether to send the alarm signal.