edisonboy

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.

Russlk

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

__________________
see my website: www.geocities.com/russlk

edisonboy

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

thanks

Ed

Russlk

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.

Attached Images

TIMER_157.jpg (18.3 KB, 636 views)

__________________
see my website: www.geocities.com/russlk

edisonboy

thanks!!!!!!

edisonboy

What is the value of R3? 680k?

thanks

Ed

Nigel Goodwin

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