In the astable configuration, the 555 timer puts out a continuous stream of rectangular pulses having a specific frequency. The astable configuration is implemented using two resistors, formula_1 and formula_2, and one capacitor formula_3. In this configuration, the control pin is not used, thus it is connected to ground through a 10 nF decoupling capacitor to shunt electrical noise. The threshold and trigger pins are connected to the capacitor formula_3, thus they have the same voltage. Initially, the capacitor formula_3 is not charged, thus the trigger pin receives zero voltage which is less than a third of the supply voltage. Consequently, the trigger pin causes the output to go high and the internal discharge transistor to go to cut-off mode. Since the discharge pin is no longer short-circuited to ground, the current flows through the two resistors, formula_1 and formula_2, to the capacitor charging it. The capacitor formula_3 starts charging until the voltage becomes two-thirds of the supply voltage. At this instance, the threshold pin causes the output to go low and the internal discharge transistor to go into saturation mode. Consequently, the capacitor starts discharging through formula_2 till it becomes less than a third of the supply voltage, in which case, the trigger pin causes the output to go high and the internal discharge transistor to go to cut-off mode once again. And the cycle repeats.