How 2 wire a PIR to close a circuit (deactivate) a connection to a clocks alarm.

gra1234

My 9 year old son is working on a project that involves hooking up a motion sensor (PIR) to a clock alarm. The challenge is to get the PIR to de-activate a sounding alarm. We have the alarm and the PIR - but what should we try next?

The datasheet for the PIR we are working with can be found on this link: http://www.parallax.com/.../Default.aspx

The plan is to hook-up a small battery operated clock (1 AA battery) to the PIR sensor, so that when the alarm initially activates the PIR would require movement to prevent the alarm from ringing.

I'm a former art student with a science techie son, so any help is valued!

jmalaysia

What resets the alarm on the clock now?

kjennejohn

Hi. Your link doesn't work. Do either of you have experience soldering or desoldering electronic components? This is going to be key in your project.

Does the PIR have a relay to control something? And if so, how many contacts does it have? Two contacts suggests a simple normally-open circuit, in which case you'll have to use that to control another device, like a transistor or another relay, to turn something off. If it has three, this suggests it has a normally-closed contact too, which can be used to shut something off directly.

Good luck with your project.
kenjj

gra1234

kjennejohn and jmalaysia

Thanks for your help on this.

Not sure what happened to the link, here it is again:
http://www.parallax.com/Store/Microcontrollers/BASICStampModules/tabid/134/txtSearch/PIR/List/1/ProductID/83/Default.aspx?SortField=ProductName,ProductName
In case that doesn't work again, It is a Parralux PIR model #555-28027 that can be found on the Parralux.com website

It doesn't appear that the motion sensor has a relay. May need to purchase one. What would be a good type/size? The clock is currently powered by a single AA battery. To answer your soldering question: We own a soldering gun and solder...is there anything we should know regarding soldering electronic components?

The clock is turned off by a switch on the top of the clock, but at this point my son has dismantled the clock and he is happy to present it in it's bare bones state. His concept for this project is: if you are lying in bed and the alarm triggers - the only way to keep the alarm from continuing to sound is by motion, hence you eventually get tired of constantly having to move and give in and get out of bed!

Thanks for any help you can give.

jmalaysia

Hmmm... first off, it doesn't sound like you will want to reset the alarm with the motion detector, just to silence it while motion is detected. If you reset it then it would not resume alarming when the victim has decided to sleep in after brief movement. That being the case I would suggest you locate the "noise maker" in the alarm and see if you could disable it via relay. That way the clock will still be "alarming" but not producing any sound. Shutting it off completely would still require using the switch on the clock (not a problem since you are UP now!).

The datasheet for the PIR detector does not specify it's output- only that it is compatible with a stamp. Are you planning to use one? There are battery operated PIR detectors that come with built in relay outputs if not.

PIR detectors have a "warm up" time. The parallax model specifies up to 60 seconds to warm up, meaning it will need to be powered up at least a minute before alarm time of it will not be ready to use.