Multivibrator infrared transmitter circuit

A multivibrator is composed of transistors VT1,
VT2 and resistor-capacitor components . The working principle of the multivibrator is: Ra and R4 are the base bias resistors of VT2 and VT1 respectively. After closing the switch SA and adding the power supply voltage, VT2 is turned on first , and its collector plate is at low level "O" , this low level is coupled to the base of VT1 through VD2 and Ca , causing VT1 to cut off. After VT2 is turned on, R4, VD2 and Vr2 charge G. The result of charging is that G carries left positive and right negative charges r, which causes the base potential of VT1 to begin to increase. When the base voltage rises to a certain value, \rri is turned on, and the lower jump level of its collector is added to the base of VT2 through VD1 and C2, causing VT2 to change from on to off. After a while. VT1 turns to cutoff. VT2 is turned on. VT1 and VT2 alternately turn on and off, and the cycle continues, so q4 acts as a stable multivibrator .     Its oscillation frequency mainly depends on the charge and discharge time constant and G and wind island.     After VT1 and VT2 start to oscillate, they are turned on and off alternately, and LED2, LED3 and LEDI connected to their collectors alternately emit infrared light and red light. ． , The visible light of the LED is used to monitor whether the oscillator