Basic application of 555 frequency modulation circuit

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Crystal oscillator 2.5*2.0mm 2520 0.67M~170M OSC can be supplied at any frequency

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This circuit is suitable for applying a DC coupled FM or PPM signal to a 555 circuit configured as an oscillator.
The 555 timer can be said to be a model for combining analog and digital circuits.
Each of the two comparators C1 and C2 has an input connected to a voltage divider composed of three resistors R, and the output of the comparator is connected to the RS flip-flop. There are also output stages and discharge tubes. The output stage has a drive current of up to 200mA.
The reference voltages of comparators C1 and C2 are UA and UB, respectively. According to the other inputs of C1 and C2, the trigger input and the threshold input, the output state of the RS flip-flop can be judged. When the reset terminal is low, the RS flip-flop is forced to reset. If no reset operation is required, the reset terminal should be tied high.
The 555 Timer is a mid-scale integrated device that combines analog and digital functions. Generally known as 555, which is made by bipolar process, it is called 7555 in CMOS process. In addition to single timer, there is a corresponding dual timer 556/7556.555. The power supply voltage range is wide, which can be 4.5V~ Operating at 16V, the 7555 can operate from 3 to 18V with an output drive current of approximately 200mA, so its output is compatible with TTL, CMOS or analog circuit levels.