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555 Debouncer HELP

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Turbo Boss

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I will explain again what I need:

In my project there is a wire that is going to supply a continuous Neg- to keep the pin #2(555)triguer..... This will keep the out pin#3 HI. The Neg- will be continuous for as long as 4 or more minutes..... Then when this Neg- disapear from pin #2 ........... I want that the out pin #3 remain HI for around 30 seg more then goes to 0

Can you help me?

THX
 

Roff

Well-Known Member
To get 30 seconds, you need to change the timing resistor (pins 6 & 7 to +V) to about 300k. To make the circuit do what you want, connect the cathode of a 1N4148 diode to pin 2. Connect a 100 ohm resistor from the anode of this diode to pins 6 and 7. This will prevent the 100uF capacitor from starting to charge until you release the pushbutton. It worked on the Spice simulation I ran. The 100 ohm resistor is necessary to limit the discharge current through the diode if you happen to push the button again while the 100uF cap is charging.
 
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