PIR module help

I need a little help getting the idea I have working.

First I bought this PIR module:

**broken link removed**

I have this working fine on a 9v battery. When I wave my hand in front of it I get 3.3v on the output line.

This is where I need help. I want that 3v output to fire a relay that can switch the 9v from the battery. If anyone could help me get this going I would be very grateful!

If you read this link and scroll down to the transistor relay examples it should get you going. The transistor you choose should be able to easily handle the relay coil current. Maybe a good common transistor like the 2N2222. The data sheet can be found here. So you need to determine how much current you want to switch and it looks like any small 9 volt coil relay should work, then note the relay coil current and choose a transistor. For small low power applications I like the 2N2222 or the 2N3904 as transistors. Anyway, those links should get you going.

Ron

Thanks for the links, that worked perfectly! I ran the output to a transistor through a 2.2k resistor, then to the relay coil with a diode to protect the transistor and it is switching perfectly now! Thanks so much.

I ran into another snag, when I turn on the motion sensor I need a 5 second delay before the thing goes active. Can someone suggest the best route to take here? Also where should I interrupt the signal? Between PIR output and transistor, or transistor and relay coil? I don't want to interrupt power going into the PIR module because it takes a moment to warm up and stabilize, and I don't want false positive signals going to the relay in this time so I would prefer letting it warm up while interrupting the output signal someplace.

OK, not a problem. You need to add a delay timer circuit. A simple approach would be to use a pair of 555 timers or a 556 timer (two 555 timers in a single package). Generally called a two stage timer. The idea being the first timer is triggered off the PIR and then following a preset time period the second timer goes active and pulls in your relay. There is a problem here in how long you want the relay pulled in. Following a pre set time for the second timer it will time out and your relay will open. Nice thing about the 555 or 556 family is they can output 200 mA to drive a small relay. Personally I would let the PIR fire the transistor and let the transistor trigger the 555 timers.

Another good option would be the use of a small 8 pin little micro controller chip. This would be an ideal solution but... You need to get a handle on micro controllers and programming one to do the job. So there is more to using a uC than seen on the surface. If you want to get into programming uC chips then it's a good way to start, however, if you just have a one time application then just using discreet components is a good way to go.

This link should give you a basic idea of using a pair of 555 timers. A Google of 555 timer circuits will bring up dozens of hits.

Ron