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when the monostable is triggered the output would come on after 5 seconds and stay on for some time. switch SW2 is the reset. enter image description here how would I do this? please make it simple.

mohamed
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  • What is the actual problem you're trying to solve? Most likely there is a better solution that doesn't involve a monostable. – The Photon Mar 15 '16 at 21:00
  • 5 seconds after a switch is pressed an LED comes on for a minute. that's what i want to do. – mohamed Mar 15 '16 at 21:05
  • You could probably use two monostables for this. But waiting for the reset switch before allowing a new trigger might require extra work. The real world engineering solution would be a tiny microcontroller. – The Photon Mar 15 '16 at 21:22

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As The Photon pointed out, this would be an easy job using a small (6 or 8-pin) microcontroller such as a PIC10. But if you're not already set up to use one, that's a fairly steep learning curve. Instead you can do this with a 556, which is a dual 555, and is available from RadioShack for $2.49.

I'm going by your comment, which says you want the LED to go on for a minute after a 5 second delay, rather than being reset with a switch.

enter image description here

When the pushbutton is pressed, the first half of the 556 triggers, and the output OUT1 goes high for 5 seconds. It then goes low, triggering the second half of the 556, which goes high for 60 seconds turning on the LED.

I calculated the values of the timing components using this 555 monostable calculator.

tcrosley
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  • That won't work because OUT1 will be go low on power-up, which will trigger the bottom timer continuously until the pushbutton is pressed. When that happens OUT1 and TRIG2 will go high which will force OUT2 low until the top timer times out, then when OUT1 goes low it'll trigger the bottom timer and OUT2 will stay high forever, or at least until S1 is pressed again. You can fix it by differentiating the low-going edge of S1's output and feeding that spike to TRIG1, and differentiating the trailing edge of OUT1 and feeding that negative-going spike to TRIG2. – EM Fields Mar 16 '16 at 00:11
  • Another problem: S1 isn't doing anything. It only needs to be SPSTNO and connected between the bottom of C5 and GND, and the bottom of R3 needs to be connected to the S1 - C5 junction. – EM Fields Mar 16 '16 at 11:13
  • @EMFields Thanks again, I must have been asleep when I picked that switch. The SparkFun SMD SPST pushbuttons have four terminals, and I just blindly hooked it up without realizing it wasn't the right one. – tcrosley Mar 16 '16 at 11:55