| It is advisable to read
the page on the 555 internal block diagram before reading this.
When power is applied, C1 starts to charge via R1 and R2. When the voltage on the capacitor reaches 2/3 Vcc, pin 7 goes low and starts to discharge C1. When the voltage on the capacitor falls to 1/3 Vcc, the trigger pin 2 is activated restarting the timing sequence. C1 charges to 2/3 Vcc and discharges to 1/3 Vcc repeatedly. A square wave appears at the output, pin 3. The mark/space ratio can be adjusted by the R1/R2 ratio. |
Copyright Graham Knott 2002