I have a perimeter fence I wish to install multiple passive infrared sensors on.
I have a way of running a single power feed round he perimeter and powering all the PIR's with 12 volts. Now I need a way of addressing each PIR so that when one trips / changes state, my alarm system will know which PIR has been activated.
In other words, one of the PIR's is tripped, I need something to see that it's been tripped and send a source addressed message to an Arduino.
I'm thinking RS485 or I2C but really not sure how to modify or add on to each PIR to achieve this?
I would also need some way of optically isolating each PIR from the data cable running around my garden.
Does anyone have any ideas to point me in the right direction please?
You will need an Arduino (Pro Mini) at each "station" with an RS-485 transceiver chip.
You will need a four-wire cable to carry power and the RS-485 pair. Black telephone wire will presumably do, buried as far as possible. Power it with 10V and use the regulator on each Pro Mini to derive its regulated 5V for the PIR and RS-485 transceiver.
You invent a "packet" protocol where the master station polls each slave and listens for its reply. Packets contain a "sync" character, packet length, address, command/ response data and checksum, retransmitted if no answer in expected time.
Slow data rate - 1200 baud. The Arduinox will remember IR tripping between successive polls.
Should work OK.
Why did you refer to "optically isolating"?
Don't forget to put a sunshade over the PIRs. Not only does sunlight interfere with their operation and potentially wear/ burn them out, but the lens degrades rapidly under sunlight.
I subcribe all the sugestions.A couple of months ago I develop a small project based on RS485 and in my project I power all the nodes using a UTP cable CAT5 like a POE solution.Well it works ok but when you increse the distance for about 200 meters then the voltage drop in the cable is a problem.Just pay atention to that.
Also try to use a swithing power supply at each node, not a 78XX since with lot nodes you will need some juice to power all then.They are not eficient and in my case that reveals a problem when the number of nodes start increasing
I have a perimeter fence I wish to install multiple passive infrared sensors on.
I have a way of running a single power feed round he perimeter and powering all the PIR's with 12 volts. Now I need a way of addressing each PIR so that when one trips / changes state, my alarm system will know which PIR has been activated.
In other words, one of the PIR's is tripped, I need something to see that it's been tripped and send a source addressed message to an Arduino.
I'm thinking RS485 or I2C but really not sure how to modify or add on to each PIR to achieve this?
I would also need some way of optically isolating each PIR from the data cable running around my garden.
Does anyone have any ideas to point me in the right direction please?
The fence is 800 meters long.
Thanks in advance
Dave
RS485 as suggested and wires with low resistance because of the 800 mt. If you are lazy as me and dont want to create protocol, use the arduino modbus library.
I suggested opto isolation as the wire run is 800 meters and my yard is mainly made up of granite and dolomite, and I live on the side of a hill. So lightning is a big worry.
I can break up the 800m in to 4 zones of 200m as my property is basically a square.
Does anyone know of anything cheaper than an arduino that communicates in RS485? Perhapse a chip or something?
I need a fair amount of PIR's and putting an arduino in to each one of them is going to get expensive quickly.
I suppose I could run a umber of PIR's off one ardiuno.
Instead of using PIR's I could use IR beams. Reduce the number of units required.
I could have say, 8 sets of IR beams which would give me 8 zones. Much more economical.
But I still need a way of optoisolating the beams / arduinos from the central computer that will control the alarm system.
But with beams, afaik, you need a receiver on the other side. Or if not a receiver then a reflector, if the transmitter has a receiver in the same unit. Then the intruder breaks the beam. At least, that's how I envisage it works with beams.
(Like the Big Bang Theory episode of Secret Agent Laser Obstacle Chess.....)
I suggested opto isolation as the wire run is 800 meters and my yard is mainly made up of granite and dolomite, and I live on the side of a hill. So lightning is a big worry.
I can break up the 800m in to 4 zones of 200m as my property is basically a square.
Does anyone know of anything cheaper than an arduino that communicates in RS485? Perhapse a chip or something?
I need a fair amount of PIR's and putting an arduino in to each one of them is going to get expensive quickly.
I suppose I could run a umber of PIR's off one ardiuno.
Your thoughts?
Thanks again
You can use barebone atmegas chips with Arduino core inside them. Its just 4 bucks each or maybe less.
lalamanzi:
I suggested opto isolation as the wire run is 800 meters and my yard is mainly made up of granite and dolomite, and I live on the side of a hill. So lightning is a big worry.
And opto-isolators are going to protect against lightning?
The thing about opto-isolated sections of a network, is that each isolated section must have its own power supply. So you have to run (lots of) power wires.
lalamanzi:
I need a fair amount of PIR's and putting an Arduino in to each one of them is going to get expensive quickly.
I specified Pro Minis as being perfect for your task.
lalamanzi:
I suppose I could run a umber of PIR's off one ardiuno.
Indeed you could. About a dozen - but you have to wire them in.
(for this project)