The 555 monolithic timing circuit is a highly stable controller capable

of producing accurate time delays, or oscillation. In the time delay

mode of operation, the time is precisely controlled by one external

resistor and capacitor. For a stable operation as an oscillator, the

free running frequency and the duty cycle are both accurately

controlled with two external resistors and one capacitor. The circuit

may be triggered and reset on falling waveforms, and the output

structure can source or sink up to 200mA