555 timer help!!!

I am trying to make a 4 second delay on a 555 timer circuit, so that when I put power on it, it will start out dead, wait 4 seconds then turn on forever. All help is appreciated.

You have to invert the 555 output. A PNP transistor with current limiting resistor to the base should do it.

could you tell me more... I just tarted this 2 days ago

could you tell me in a bit more depth (like pin numbers)?... I just started 2 days ago... I'm working on reading scimatics (any tips on that will also be appreciated! ) but they still look alitle confusing...

thanks

Ed

This is what I had in mind: The 4 second time is set by R1 and C2, the trigger is caused by C2 which holds pin 2 low at the time power is applied. C2 charges thru R2 in less than 4 seconds so the timer does not re-trigger. C3 is just the recommended bypass cap. The output of the 555 does not go all the way to the power supply voltage, so the yellow LED is used to drop 2 volts and insure that the 2N2907 is off when the 555 output is high. Any questions, you can email me or post here.

thanks!!!!!!

What is the value of R3? 680k?

thanks

Ed

edisonboy said:

What is the value of R3? 680k?

Click to expand...

I would have said 680 ohm, as it's labelled.