will it time out

i know that a 555 will time out when pin 2 is triggered by a push button then released, my question is, will it still time out if that push button was a switch and the switch was left on.If not, could someone give me precise detail description and wiring diagram if possible on how to achieve this in monostable mode. thank you kindly

Posted by lorsal (lorsal@iprimus.com.au) on 27/10/2003, at 14:11 GMT

555 trigger

The 555 will not time out if you keep the switch closed. The output is high all the time the trigger (pin 2) is held low with the switch closed. However, it is easy to achieve the action you want by adding a capacitor and an extra resistor to the trigger connections:

You should already have a resistor between pin 2 and +V, its value is not critical but I will use 33k for example. Insert a 0.1uF capacitor between pin 2 and the junction of the 33k resistor and switch; then add another 33k resistor between pin 2 and +V (positive supply). The capacitor allows the 555 to respond to the action of closing the switch, but if you keep the switch closed it will be ignored.

I hope that helps.

Posted by John Hewes on 30/10/2003, at 12:24 GMT