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[Travler64]

I need a 5 second logic delay but I need it to work like this....
If my logic signal goes from High to Low, I need to delay the Low for 5 seconds then be able to reset when the alarm that caused my signal to go Low clears...
Basically I have several alarm inputs, when one of these inputs goes low this will energise a relay through a relay driver, but these alarm inputs can be only momentary bounces so I need to delay the relay at least 5 seconds to make sure the alarm is real. This is all done with logic gates and a UDN2596A driver....
Any ideas??

 

[melone]

This is very easily done with a simple 555 timer circuit. You can set it to trigger on either the high-to-low or low-to-high transition of an input signal. The time that the output is "ON" is determined by an external resistor and capacitor. National Semiconductor (

http://www.national.com)

makes the LM555 timer IC that should due the trick.

Just a few more quesitons. Are there any unique enviornmental requirements for this circuit (Temperature, Vibration, Humidity, etc.). Are there any space requirements? Cost requirements? Life expenctance requirements? etc...


Hope this helps!

 

[Travler64]

Melone
Thanks for your idea, but I have a question.
Let me see if I understand this....
when my logic signal goes Low into my relay driver, this enables the relay, but I want a 5 second delay before the relay driver so when my logic goes low, the relay driver basically does not see it for 5 seconds but I also need it to stay low until my alarm condition clears and the logic line goes high again and you think I can do this with a 555 timer.
So basically I can set a timer to trigger on high/low wait 5 seconds then the output of the 555 goes low and stays low until I reset the timer?
Is this correct?

 

[melone]

You can use the 5 second delay to latch on (turn the output low) your output. This can be accomplished by using a D flip-flop with edge triggering. Let me put something together tonight and I can email the solution to you.

Hope this helps.

 

[Travler64]

Cool. Thank you sir...
I look foward to seeing it.

 

[Travler64]

Melone, just checking back to see if you have come up with a circuit......

 

[melone]

There are a couple of differenct circuits that I can think of that will do the trick. I will email you a copy of just a couple of hand drawn circuits is you send me your email. Just send me an email and I will reply to it with the circuits attached.

Mark_Melone@yahoo.com

 

[Travler64]

Mark, making sure you received my e-mail.
If not, please send to Travler64@yahoo.com
Thank you.


Jeff