555 Debouncer HELP

I already build this project and its working. The relay is working for around 30 seconds.
But if I keep the button close for around 40 sec when I release the button the relay does not work.

http://www.talkingelectronics.com/FreeProjects/555/555-SwDebouncer-1.gif

How do I make this circuit so I can keep the button close for a very long time and when the button is released then the cut off time begin to work.


THX

Posted by malibu 307 on 18/08/2003, at 03:00 GMT

555 Trigger behaviour

The 555 timing period starts as soon as you press the trigger button (making pin 2 go low, 0V). The 555 will keep its output high (relay on) all the time the button is pressed even if the timing period is over.

By the time you release the button after 40s the timing period is over so the 555 output goes low (relay off) as soon as you release the button.

To achieve the action you want you need to have a more complex triggering circuit:

(1) Insert a 0.1uF capacitor between pin 2 and the junction of the 47k resistor/push switch; then add another 47k resistor between pin 2 and +V (positive supply). The capacitor allows the 555 to respond to the action of pushing the switch, but if you hold the switch closed it will be ignored.

(2) To achieve tiggering when you RELEASE the push switch you should replace it with a "push-to-break" switch which opens when pushed. Standard push switches are "push-to-make" because they close when pushed. For more information on switches see www.kpsec.freeuk.com/components/switch.htm

Posted by John Hewes on 18/08/2003, at 10:40 GMT

555

Hello John, Thank you for your help. I think I explain bad what I need. I will try to explain again.

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. This Neg- is continuous for as long as 3 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 to solve my problem.

THX

Posted by malibu 307 on 18/08/2003, at 20:59 GMT

555 circuits

You can't do this with a single 555, but you could try a combination of 555 circuits. For example use a 555 bistable to control the relay (triggered by your input) and use a 555 monostable to give the delay you require before it activates the bistable's reset. You will need to invert your input signal (swop high and low states) to trigger the monostable.

Details of the bistable and monostable circuits are on this website. You can make an inverter with a 555 too! Connect pins 4,6,8 to +V (positive supply) and pin 1 to 0V. Pin 2 is the input, pin 3 is the output. Pins 5 and 7 are not connected.

Posted by John Hewes on 21/08/2003, at 10:54 GMT

I found what I was looking for :-)

I just find the circuit I needed.

http://home.cogeco.ca/~rpaisley4/LM555Delays1.GIF

I use circuit #2 Negative Recovery

I change the the 1M for a 15K and the 1uf for a 22uf and my project its working awesome.

Thank you for your help.

Posted by malibu 307 on 23/08/2003, at 20:00 GMT

A great 555 circuit!

A clever solution - so it is possible to achieve the result you wanted with a single 555!

Posted by John Hewes on 23/08/2003, at 21:37 GMT