On 12/23/2020 8:38 PM, Daniel Fynn wrote:
I have built a 555 timer monostable circuit that works fine(when pin 2, the trigger is momentary grounded the output, pin 3 goes high for about 10 seconds before going low again) but now, i need a circuit that will work the same way even when pin 2 (trigger) is held low for say 5 minutes. Meaning when pin 2 is held low for a long time, the output will go high for the same 10 seconds and then will go off. it should stay off until pin 2 is removed from ground and sent back to ground again before the output can go high again.
The circuit is for a project that has an infrared obstacle sensor as its input and operates a light when it detects a hand. What I want is even if the hand stays there for a longer time the light should go off after 10 seconds until the person removes the hand and brings it back before the light will come on.

Â*How about a differentiator?

If the sensor input is changed slowly, (slow fall time) that might not
work and you would need a schmitt trigger before the differentiator.

http://evalidate.in/lab1/pages/RC/RC...ntiator_I.html
This shows a square wave, But your transition from B+ to 0V will give a
negative pulse to trigger Pin 2.

Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* Mike


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