This Timer is a highly stable controller capable of producing accurate timing pulses. With a monostable operation, the delay is controlled by one external resistor and one capacitor.
With astable operation, the frequency and duty cycle are accurately controlled by two external resistors and one capacitor.
555 Datasheet Fairchild
• High-Current Drive Capability: 200 mA
• Adjustable Duty Cycle
• Temperature Stability of 0.005%/°C
• Timing From μs to Hours
• Turn off Time Less Than 2 μs
Application Information ( 555 datasheet fairchild )
When the low signal input is applied to the reset terminal, the timer output remains low regardless of the threshold voltage or the trigger voltage. Only when the high signal is applied to the reset terminal, the timer’s output changes according to threshold voltage and trigger voltage.
When the threshold voltage exceeds 2/3 of the supply voltage while the timer output is high, the timer’s internal discharge transistor turns on, lowering the threshold voltage to below 1/3 of the supply voltage. During this time, the timer output is maintained low. Later, if a low signal is applied to the trigger voltage so that it becomes 1/3 of the supply voltage, the timer’s internal discharge transistor turns off, increasing the threshold voltage and driving the timer output again at high.