# 555 timer - pin functions

Pin | Name | Description
--- | --- | ---
1 | ground | 0 V supply
2 | trigger | When the pin voltage falls below 0.33 Vcc, the timer is triggered and the output goes high. In the monostable configuration a high to low transition on the trigger pin starts the timer.
3 | output | The output pulses during astable operation and goes high for a set time in monostable operation.
4 | reset | If reset is not used, connect it to Vcc. If reset falls, a high output will be forced low.
5 | control voltage | For reliable operation add a 10 nF capacitor to ground on this pin.
6 | threshold | Detects when the voltage on the timing capacitor rises above 0.66 Vcc and resets the output when this happens.
7 | discharge | Provides a discharge path from the timing capacitor to ground when the output is low.
8 | Vcc | Positive power supply voltage.

## See also:

- 555 timer