The working principles of the 555 timer are different in three different working modes:
1. Monostable mode
In the monostable working mode, The 555 timer works as a one-shot pulse generator. When the trigger input voltage drops to 1/3 of VCC, it starts outputting pulses. The output pulse width depends on the time constant of the RC network composed of timing resistors and capacitors. When the capacitor voltage rises to 2/3 of VCC, the output pulse stops. The pulse width can be adjusted according to actual needs by changing the time constant of the RC network.
2. Bistable mode
The 555 chip in bistable working mode is similar to a basic RS flip-flop. In this mode, trigger pin 2 and reset pin 4 are connected to high level through pull-up resistors, threshold pin 6 is directly connected to ground, control pin 5 is connected to ground through a small capacitor (0.01 to 0.1μF), and the discharge pin Pin 7 is left floating. So when pin 2 inputs a high (error should be low) voltage, the output is set, and when pin 4 is connected to ground, the output is reset.
3. Astable working mode
In the astable working mode, the 555 timer can output a continuous square wave of a specific frequency. Resistor R1 is connected between VCC and discharge pin 7, resistor R2 is connected between pin 7 and trigger pin 2, and pin 2 is short-circuited to threshold pin 6. The capacitor is charged to 2/3VCC through R1 and R2, then the output voltage flips, the capacitor is discharged to 1/3VCC through R2, then the capacitor is recharged, and the output voltage flips again.
Extended information?
Uses of 555 timer
1. The 555 monostable circuit can be used in daily life such as corridor delay lights, time switches, and delay switches. Time-breakers can be used to measure frequency, large-capacity capacitance, rotation speed, etc. in measurement circuits.
2. The bistable circuit of 555 is widely used in electronic measurements. It can be used as a Schmitt trigger to shape various waveforms. In life, this kind of circuit can be used as various light-controlled switches and temperature-controlled switches.
3. In the alarm, the 555 astable circuit can be connected as an oscillator to form an audible and visual alarm circuit; it can form an ultra-low frequency oscillator to drive various small lights to emit flashing light; in the measurement circuit It can be used as a simple waveform generator; due to the large driving current of NE555, NE555 can be used as an oscillator in an infrared remote control circuit to directly drive the infrared transmitter tube.
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