Old burglar alarm PIR connect to Arduino?

I have recently moved house and there are PIR sensors in most of the downstairs rooms. These are connected to a broken burglar alarm control panel. I have disconnected the alarm itself, but left the 12V power supply to the PIRs.

I would like to connect the PIR outputs to an Arduino and then make a HTTP POST to a local webservce everytime the NC output from the PIR changes to NO.

I am VERY new to Arduino and haven’t even yet purchased my first board, but wonder if this could be a viable Arduino project to get me started?

Can anyone offer any pointers or recommend hardware? I’ve been looking at the POE powered boards.

pir_datasheet.pdf (1.09 MB)

If you are very new to Arduino, buy an Arduino Uno and a optocoupler. See if you can detect 12V with the optocoupler. Do you have a multimeter ?

Do you want a single central Arduino or an Arduino in every PIR module ? An Arduino with ethernet in every PIR module is not a good idea. It will be expensive, and you need ethernet cables.

The central Arduino could be an Arduino Uno + Ethernet Shield, and you can upgrade that later to Arduino Mega 2560 + Ethernet shield.
How many PIR modules do you want to detect ?

I hope you are a experienced software engineer, because an alarm may not be missed. You have to be aware of that when writing the code.

Assuming the normally-closed relay contacts are isolated from the rest of the PIR sensor, you can connect directly to your Arduino. There is no need to use an optocoupler. Connect one contact to ground and the other to an Arduino input. Use code to enable an internal pull-up resistance.

The basic alarm system is a simple matter of looping around checking that each input has not changed. You will also need to be able to arm and disarm the system.

All except the disarm (I assume you will want a PIN code) is simply reading a switch. This is done by connecting a 10k resistor (or use internal pull-up) from 5v to a digital put and the switch to gnd.

You will also need to have a delay after arming the alarm to enable all sensors to settle down and you to exit.

To enter, you need a delay on the entry to enable the PIN to be entered. You could use a remote also.

Before the alarm is activated, you may wish to check all except exit are closed.

Do some research on alarm features then start with small steps. Read a switch. Then loop to read many switches. Add reading a keypad.

Once you get the basic alarm going then look at sending the alarm elsewhere.

Weedpharma

Peter_n - Thanks, I would prefer a single central Arduino, as the PIR cables are all terminated to the same point (utility room, which is where network router and POE switch are located). There are 5 PIRs and 2 magnetic door contacts.

I see the Mega 2560 has 16 analogue input pins.

I am not using this as a burglar alarm, just to see what rooms we use around the house and at what times.

Thanks

Archibald, thanks for the info. I think the NC contacts on the PIR are isolated. How can I check this?

Weedpharma, you and Archibald both mentioned internal pull-up - what is this?

pigeonboy99: Archibald, thanks for the info. I think the NC contacts on the PIR are isolated. How can I check this?

With the PIR sensor powered-up, measure the voltage between ground and a relay contact and then between +12V and a relay contact. If isolated, both readings will be zero.

pigeonboy99: Weedpharma, you and Archibald both mentioned internal pull-up - what is this?

See: https://www.arduino.cc/en/Reference/PinMode

pigeonboy99: Archibald, thanks for the info. I think the NC contacts on the PIR are isolated. How can I check this?

Alarm PIR contacts are normally isolated.

Weedpharma

most PIR of modern type have 12VDC power, and a set of contacts. oftehn there is an other contact for tamper. this last one is to make sure the cover is on.

you feed the sensor 12 volts. the relay is normally closed.
you connect your signal wire, and if you detect 12 volts, you know the circuit is complete. when there is movement, the circuit opens.

since you have 12vdc power, you can use a resistor and an LED to watch. all the LED’s should be lit all the time, when there is movement, the LED will go out.

if you can make that happen, then you can just add a very simple connection to your arduino.

instead of one resistor, use 2. the total should be between 900 and 1,200 ohms.
you need to drop 12v to about 4.5 volts. not over 5 and not under 4.5 volts.
.the digital input pins need over about 3.5 volts to ‘see’ a voltage. the closer you get to 4.5 the less chance of a problem. getting too close to 3.5 opens the door for voltage droop and not registering a problem.

if you have a 620ohms then a 470ohms then the LED, in that order.
you should have about 4.5 volts between the resistors.

if you have this, then you can connect that to the input pin on your arduino.

if your sensor has 4 wires to it, and you have access to all 4 wires, you might be able to feed the relay with 5 volts and then get 5 volts back when there is no movement.

if that is the case, then you can feed that 5v directly to your digital input pin.

to protect your arduino from higher voltages, many will tell you to put in some sort of protection. an optocoupler is a transistor that uses an LED on one side and a sensor on the othe side. the voltage from your relay/sensor would light the LED and then that would have the output of the opto change state.

the output of an opto is a transistor. you feed it power by putting your 12v into a resistor then connect to the opto , then connect the other pin of the opto to ground. when the opto goes high because of the LED getting power, the transistor completes the circuit and the power being fed from the resistor is brought to ground. this will have the voltage between the resistor and the opto will go to near ground.

the will have the effect of inverting the signal. when you have 12v from your pir to the input of the opto, the internal LED will light. the otput of the opto will bring the voltage to ground and the wire between the resistor and the opto will be near 0. when you have movement, the 12v from the PIR will go to zero. the internal LED will dim, the output side of the opto will no longer bring the voltage to ground and the wire between the resistor and the opto will rise to the voltage that is present on the high side of the resistor. we expect you will use 5 volts for the opto on the output side. since the wire between the resistor and the opto will go high and low as the opto input goes low to high, you can bring that wire into the arduino digital input pin.

google optoisolator there are lots and lots of tutorials.

There is evidently some difference of opinion here.

If the relay contacts are fully isolated then in my view they can simply be connected directly to ground and to an Arduino input pin.

The only thing you may wish to consider is protection from lightning hitting the house!

Archibald: There is evidently some difference of opinion here.

If the relay contacts are fully isolated then in my view they can simply be connected directly to ground and to an Arduino input pin.

The only thing you may wish to consider is protection from lightning hitting the house!

old installation, installer could have used 3 conductor wire....

I think we are just offering ideas

I have old alarm system around 500 quantities and everything we had installed at retails stores,we want to monitor it from one place,how to interface these DSC panel for monitoring?

I need Ethernet shield interface module..if you have an idea..kindly route me...