Multivibrator double flash light

The multivibrator double flash light circuit is derived from the double flash light circuit of the car. It is a classic mutual push and pull circuit. After power is turned on, LED1 and LED2 flash alternately, that is, the two light-emitting diodes are turned on in turn.
The principle is excerpted from the network
. The self-excited multivibrator is also called an astable circuit. The collectors of the two tubes each have a capacitor connected to the base of the other tube, which plays an AC coupling role and forms a positive feedback circuit.
　　This circuit is an astable multivibrator circuit. The two triodes V1 and V2 in Figure 2 work alternately between saturation and cutoff states, that is, when V1 is saturated, V2 is cutoff, and when V1 is cutoff, V2 is saturated. The two states are periodically interchanged, and the collector output waveforms of V1 and V2 are similar to square waves.
　　When VCC is connected, V1 and V2 obtain forward bias from R2 and R1 respectively, and C1 and C2 are also charged through D1, R3, D2, and R4 respectively, as shown in Figure 4.
　　Figure 4 When VCC is powered on
　　Since the characteristics of V1 and V2 cannot be 100% the same, assuming that the current gain of a transistor V1 is higher than that of another transistor V2, V1 will enter the saturation state before V2. When V1 is saturated, C1 forms a discharge circuit composed of VCC, R1, and V1CE to discharge. A reverse bias is formed at the V2BE pole, that is, the voltage at point A is negative (about -2V), causing V2 to turn off and V1 to turn on. Since the c and e poles are connected at this time, the potential at the c pole is close to the negative pole (grounded in our figure, that is, close to 0V). Due to the coupling effect of capacitor C1, the base voltage of V2 is close to the negative pole → no base current will be generated, that is, Ib=0A → then V1ec is disconnected, and at the same time, C2 is charged to VCC in a short time through D2, R4 and the BE pole of V1, as shown in Figure 5.
　　Figure 5 C1 discharges, C2 charges the circuit
　　V1 is turned on, Q2 is turned off. The situation is not stable. After C1 is discharged, the capacitor C1 is reversely charged by VCC through R1 and V1CE. When it is charged to 0.7V, that is, the voltage at point A is about 0.7V. At this time, V2 is biased and enters the saturated conduction state. C2 is discharged by VCC through R2 and V2CE. Similarly, V1BE is reversely biased, V1 is turned off, and C1 is charged to VCC in a short time by VCC through D1, R1 and V2B-E.
　　Figure 6 C2 discharges, C1 charges the circuit
　　Similarly, after C2 is discharged, the capacitor C2 is reversely charged by VCC through R3 and V2CE. When it is charged to 0.7V, that is, the voltage at point B is about 0.7V, V1 is biased through R2 and turned on, and V2 is turned off.
　　This cycle is repeated, and all two LEDs flash alternately. Changing the resistance of resistors R1 and R2 or the capacity of capacitors C1 and C2 can change the flashing speed of the LED.