Monostable
 

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.

Monostable
 

On Wed, 23 Dec 2020 18:38:29 -0800 (PST), Daniel Fynn
wrote:

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.

What you need is what is called edge triggering. A simple way to
implement this, is to use a capacitor in series with the trigger line.
You will also need a pull-up resistor and a diode.

Try this:

https://www.google.com/search?q=555+...e+edge+trigger

Monostable
 

On Thursday, December 24, 2020 at 2:00:19 PM UTC, HW wrote:
On Wed, 23 Dec 2020 18:38:29 -0800 (PST), Daniel Fynn
wrote:

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.
What you need is what is called edge triggering. A simple way to
implement this, is to use a capacitor in series with the trigger line.
You will also need a pull-up resistor and a diode.

Try this:

https://www.google.com/search?q=555+...e+edge+trigger
Thanks

Monostable
 

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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