Whole house PIR sensors

Dear Arduino Gods,

I'd like to have PIR sensors placed throughout my under-construction house. We do not have drywall yet and I'm doing all the work myself. I'd like to have an Arduino Ethernet with PoE in a centralized location in the house connected to a PoE Ethernet switch for both power and connectivity.

I've figured that I'd like to (ideally) have about 17 or so PIR sensors in locations at the most 15-20 meters from the Arduino (most would be closer).

I'd assume that the longer the wire, the more interference it would pick up. In several other threads a pull up resistor was mentioned. What size/kind? Does it depend on the length of the wire? (or a more basic question: how does one determine what the correct resistor would be?)

Would category 6 Ethernet be an appropriate wire to use from the Arduino to each PIR sensor? Would using something larger like thermostat wire (18 gauge (thermostat) vs 22 gauge (cat 6) vs 24 gauge (cat 5)) be a better idea (less voltage drop?) or would that increase the possibility of interference?

The PIR sensor I'm considering is based on the tests from this video. It appears that the Zilog ePIR sensor can be used either in a hardware interface mode or via a serial interface. Would using this sensor in a serial interface mode make it more reliable/possible (less interference)?

It appears (to me) that these PIR sensors can be used with analog input or digital. Am I going to run out of input pins? I've seen references to charlieplexing, but it looks like to me that that type of thing is for output. Am I wrong? When trying to gather input from multiple sensors, what are the options? (I'm clearly very new at this.)

Is there a magic number of input sensors that I should consider which would make my life a lot easier? Meaning: If there was a device which enabled input of 16 sensors but 17 sensors would mean lots of headache, etc.

I've spent the last two days reading Getting Started with Arduino 2nd Ed, Environmental Monitoring with Arduino, and Arduino Projects to Save The World, but I haven't purchased any Arduino kit yet. My head is swimming in the possibilities but I haven't committed to anything yet. I feel like I know what I'd like to do, but I'm missing huge portions of the vocabulary and hands-on experience to know if what I'd like to do is possible/reasonable. Can anyone help me out? Thank you very much.

  • Peter

tl;dr: what keywords to Google to figure out how to successfully put PIR sensors all over my house? Is it possible?

Just wondering if you would be better off with some sort of Xbee or radio network. The sensors you linked don’t have ethernet so you will be having something like 17 x $80 for the ethernet boards plus 17 x $12 for the sensors. That’s $1564 already.

Those sensors seem to have some sort of serial output, so you might be able to hook a few up to a single processor (eg. all the ones in one room).

I’ve figured that I’d like to (ideally) have about 17 or so PIR sensors in locations at the most 15-20 meters from the Arduino (most would be closer).

Or are you talking about a single Arduino? In which case it would need 17 serial inputs.

If the sensors output a simple yes/no line, then you could probably do that fairly easily. For example, a 16-port port expander could simplify things.

eg. Gammon Forum : Electronics : Microprocessors : Buttons, I2C, interrupts and port-expanders

Would category 6 Ethernet be an appropriate wire to use from the Arduino to each PIR sensor?

Sounds like an overkill, especially if it just raises an on/off signal. I would be inclined to get a couple, a reel of wire, and experiment. However if interference is an issue you could turn the signal into a balanced one, eg.

http://www.gammon.com.au/forum/?id=11428

My head is swimming in the possibilities but I haven’t committed to anything yet.

My advice is to get an Arduino (or two), get some sensors, some wire, and experiment. Your experiments with wire slung over the floor in a real-life situation will reveal more than us forum guys speculating.

Yeah, I was thinking one Arduino and all of the sensors homerun into that one Arduino. Basically I'm trying to avoid the $1564 price tag (closer to $284).

That expander is exactly what I hoped would exist (but didn't know what to look for).

[quote author=Nick Gammon link=topic=129062.msg971205#msg971205 date=1351200437]
Sounds like an overkill, especially if it just raises an on/off signal.[/quote]

When you say "sounds like overkill" do you mean a simple 24 gauge pair (or however many wires are needed) would usually work for something like this?

If there's a likely chance that this idea would work, I can move forward. I didn't want to get started and then find out something like "everyone knows that only jumper wires shorter than 1 foot would work" or something to that effect.

Knowing that technologies like RS485 exist is exactly the type of info that I was missing.

I'm going to be experimenting as soon as I can get some stuff ordered. Thank you so much for responding.

  • Peter

mrptb2:
When you say "sounds like overkill" do you mean a simple 24 gauge pair (or however many wires are needed) would usually work for something like this?

Thinking about it some more, you probably need to supply power, so you need at least 4 cores. Probably at that rate the twisted pair is not a bad idea, as you could always add in the RS485 chips later, even if you don't at the start.

Half the price...

... reputable dealer ... USPS delivered orders from MN to TX within two days. I believe the one on DigiKey is a newer model. They appear to be functionally identical.

Bear in mind: Operates from 2.7 V to 3.6 V power supply.