I've got this motion sensor circuit all put together and connected to my old laptop turned digital picture frame and it's working very well. http://forum.allaboutcircuits.com/showthread.php?t=28653 Only problem now is that the motion trigger stays on for about a second and every once in a while it stays on long enough to turn off the computer.

I'm wondering if anyone knows of a simple/low space way to make the relay trigger for 1 second only if the motion sensor is triggered twice in say 5 seconds. I thought about using a flip-flop, but I'm not sure how to set these up to achieve this. Maybe a J-K flip-flop with one input attached to a 555 timer with a heavy duty cycle?

I guess the other option would be something like a PIC, but I'd really like something that would use a little less space than either of these options.

Anyone have any ideas here? Thanks.

 

nothing???

 

It's the "twice in 5 seconds" that stops me.
Another way is to use a 555 as a one shot so the PIR can stay on as long as it wants and the computer only sees a blip.
That's the best I can think of right now.

 

Great idea! I thought about using a 555 for the input to a flip-flop, but that would be more than I really need here I guess. I could just use it to drive the relay or use the 555 to control a second transistor in series with the one attached to the motion sensor output. That should definitely take up less space than a PIC. Thanks.