Multi-vibrator circuit based on 555 chip

Crystal oscillator

Quartz Oscillator 3225 20M OSC

Multivibrator: Using deep positive feedback, the two electronic devices are alternately turned on and off by RC coupling, thereby generating a square wave output oscillator. Often used as a square wave generator. A multivibrator is a self-excited oscillator that produces a rectangular wave, also called a rectangular wave generator. "Multi-harmonic" means that the rectangular wave contains rich harmonic components in addition to the fundamental component. The multivibrator has no steady state and only two transient states. In operation, the state of the circuit is automatically alternated between the two transient states, thereby producing a rectangular wave pulse signal, often used as a pulse signal source and a clock signal in the sequential circuit.
The circuit diagram and waveform diagram of the multivibrator are shown in Figure 6-4. After the power is turned on, Vcc charges capacitor C through resistors R1 and R2. When the capacitor is powered on vC=2/3Vcc, the threshold input terminal 6 is triggered, the comparator C1 is turned over, the output voltage Vo=0, and the discharge tube T is turned on, the capacitor C is discharged through R2; when the capacitor voltage Vc=1 /3Vcc, comparator C2 operates, and the output voltage Vo becomes high. C discharge is terminated, charging is resumed, and the cycle is repeated to form an oscillation.
From the analysis, we can know:
a) The oscillation period T and the duty factor D of the circuit are only related to the external components R1, R2 and C, and are not affected by the change of the power supply voltage.
b) By changing R1 and R2, the duty factor can be changed, and the value can be adjusted within a large range.
c) Changing the value of C, the period can be changed separately without affecting the duty factor.
In addition, the reset terminal 4 can also input one control signal. When the reset terminal 4 is low, the circuit stops.