Using PIR With An I/O Device?

Hi all,

I'm currently looking for a solution for what initially seemed like a rather simple problem. Basically, what I’m trying to do is find some type of PIR/Motion detector that will work with an I/O device while not overcomplicating the install with a full alarm panel or any other unnecessary hardware, etc. These PIR devices will be used indoors within an office type environment where pretty much any motion detected, after hours, would constitute an alarm event.

I’ve had great luck recently using Optex Beams outdoors along with an Inovonics receiver in order to capture/transmit alarm events. This signal is then sent to an Axis P8221 I/O device which sends the alarm event via SMTP to a queue based alarm software. Given the success with those products, I began to first look at Optex PIR devices; namely the CX-702 given that, from what I gather, I need a device with a “Form C” relay to make this work? I believe that Honeywell has whole host of devices that are capable of this as well.

One option I considered was using a CX-702Ri along with the Inovonics receiver and Axis P8221 I/O. That option is somewhat expensive though given the added cost of the receiver and the requirement of more expensive PIR devices. Aside from that, I also don’t like using wireless/battery powered devices unless there really is no other way around it.

My second option is to put together a wired solution, but which features are required within a wired PIR detector to work with the P8221, or any other capable I/O device? In addition to that, what’s the best way to get power to those PIR devices? I’ve researched and really don’t understand how that works, even when connected to a traditional alarm panel. Is there some sort of power distribution board/box that would power a given number of these devices independent of an all out alarm panel? Aside from power, I’m assuming that the “Normally Closed” alarm wire would end up going to the I/O device itself. I’ve read the following two IPVM articles - PIR Detector Selection Guide and Inputs/Outputs Tutorial, which were a great help, but I still have some confusion on the actual install portion of the puzzle:

Any help would greatly be appreciated!

Thanks in advance :-)


Get an Optex RX-40PI (commercial warning, I sell that model PIR, along with a lot of other people), and run the N/C out to an Altronix RB5 module (the world's best relay, which I do not sell, sadly).

The CX-702 is, frankly, overkill. It does have an alarm out, which is nice, but the RX-40PI and the RB5 duplicates the functionality for about half the price. Plus the RX-40PI has pet immunity, which is nice. The CX-702 is for extremely large areas and the RX-40PI is for relatively small areas, say 40 x 40.

Basically, you'll run the alarm out from the motion into the alarm panel and also into the relay. The NC contact on the motion is a momentary, and you need a latching relay, which where the RB5 comes in. You'll also power the relay with the 12VDC coming off the panel. Easy peasy.

Here's a quick definition of Relay types:

  • Form A: This is the Single Pole, Single Throw (SPST) type, where the circuit is normally open and the relay contacts close when the relay coil is energised. (Think of your hand as the coil, and turning a lightswitch ON is the contacts.)
  • Form B: This is the Double Pole, Single Throw (DPST) type, that functions in the opposite way - contacts are closed when no power is applied, but open when power is applied. (Your hand is the coil, turning a lightswitch OFF is the contacts.)
  • Form C: If you stick one relay of each of the above types together, it becomes a SPDT (Single Pole Double Throw) relay. This is harder to visualize, but one hand would simultaneously turn two opposing switches ON / OFF. Both relays are powered by the same coil, but depending on the type of circuit you need to make, a SPDT is 'universally useful'. SPDTs are also called 'Form C' relays.

(If you are wondering, a DPDT (Double Pole Double Throw) relay is two switches together that throw the same direction with one coil.)

When it comes to which 'throw type' is best, it depends on the circuit. For example, If you want a camera to turn on a warning LED when it detects motion, you need a 'normally open' set of contacts. When the coil is energized, the circuit closes.

However, if you want to use a motion sensor, you probably want a 'Normally closed' set of contacts - the electronic circuit is complete and stable until the sensor detects movement and 'breaks' or opens, the circuit. This wakes the camera up to a big change in the normally quiet circuit.

These logic examples are very simple, and not always how 'relay forms' are used. Often relays are used to allow small amounts of DC electricity to change large amounts of AC electricity. How relay logic is applied can be very specific and potentially dangerous if misunderstood.

Also: there is an 'alternate' definition of Form B relay that presumes two circuits are normally open/closed and then closed/opened by the energised coil. However, most (low-voltage) electronics do not use this definition.

Hey all,

After working on this project off and on as time allowed, I wanted to update this after finally coming up with a complete and working solution. It appears that I was overcomplicating things from the start and after getting all the pieces in hand, the solution is actually much easier than originally planned. After taking all of your suggestions into consideration, I picked up an RB5 module and the necessary detectors and here's what I ended up with for a wired solution:

  1. Honeywell HPS123 Power Supply
  2. Optex RX-40PI motion detector
  3. Bosch DS-DS939 360 degree motion detector

And the wirelss solution:

  1. Inovonics EN4216MR 16-zone wireless receiver
  2. Optex EX-35R wireless motion detector

As mentioned, both solutions connect to an Axis P8221 I/O device. The wireless solution integrates just as it did with my Optex beams scenario (motion detector -> wireless receiver -> wired to P8221). With the wired device, it turns out that I didn't need a relay at all. All I did was send power to each motion detector and then send both alarm wires directly into the P8221 (one went to Common, the other to one of the 8 inputs). Brian: your description didn't really click with me until I was finally able to get all the pieces together (including the relay) and start wiring things up. That's when I realized that I could skip at least one piece of hardware in the process. Moving forward, I will experiment with different detectors, but since I got the architecture down, things will be much easier moving forward.

Anyway, thanks again for the suggestions and support!

Yeah, the relay was because I thought the PIR would give you a momentary, not latching, contact, and was worried it wouldn't be enough. Good to hear you didn't need it.

Thanks for following up.

Awesome! Thanks for the update.