Wiring Old Alarm System Into Computer For Monitoring?

[dinki]

Hey guys, I purchased a home that has a wired alarm system installed. I think the control keypad says it's a Honeywell, but I'm not certain. The circuit board (brains) of the system no longer exists. It was ripped out at some time in the past, but I have access to all the wire runs. I know that we have magnetic switches on all the windows, a motion detector in the living room, and a siren/horn located in the attic.

What I'd like to do is wire any of the above to a computer I have serving as my digital video recorder. I am handy with a soldering iron and am not afraid to hack around with software. What I really need to know is what do I need to do to get feedback from the switches and motion detector. I'm assuming that I will need to apply 5V dc and detect if the switch is open/closed . What kind of amperage do I need to use? Will the long wires be a source of resistance? What of the motion detector? How does it 'work'? Any ideas on what kind of power I need to energize the siren/horn? Is there any software out there to do what I'm looking to do (ie detect changes in switch states)?

I'm thinking that the parrallel port would be the easiest to wire together, but perhaps a PIC micocontroller would be better suited?

Thanks for the help....

 

[mramos1]

How many wires are you talking about. That will help pick a direction. I like the microcontroller idea. The parallel port has some power as well. The siren you will need to drive, so no matter what you will need some external circuit and software.

Did you google for this. Seems like someone has done something like this. I have an old one at the office I did, that used serial port to monitor a 16F84 (way back), you can use as a starting point. I have termperature monitor, power monitor, etc. The power monitor was a normally close 120V relay contact, so same process for you PIR and window switches. Mine sent a message to my cell phone, and I used the siren in the existing alarm. Software if I can fine it was Pic Basic Standard. It is very old and crude but still works.

 

[dinki]

Thanks for the reply. I've done a little more research and I think I'm going to use the PIC 16F877 with a Max232 for serial out to the PC.

I took a look at the wiring last night. I'm seeing a total of nine wires that went into the panel. I know that I have one run to the siren/horn, another to a motion sensor in the living room and the others go to seperate 'zones' (multiple window switches wired together). A total of 7 zones exist including the motion sensor.

Any clue on how many volts/amps it takes to run the horn? I know there was a 12V battery backup in the old system. Also, any clue on how the motion detector works and how to read it?

 

[ericgibbs]

hi dinki,
The window and door switches will most likely be normally closed switches, wired in a series loop.
As any magnetic/switch is opened the alarm will be triggered.

Its possible you may have more than one series loop.
eg: all downstairs switches in one loop and all the upstairs switches in another loop. Usually referred as 'zones'.

CAUTION:
as you didn't do the original wiring yourself, check the ends of all the wires in the control box with a voltmeter to ensure they are not wired into any potentially lethal voltage.

Once you are sure its safe to proceed you can check these loops by using a simple buzzer/meter across the wire ends in your control box.

Close all the doors and windows that have a switch and buzz out the zones.
As you open a window for test the buzzer should stop.

The motion detector could be a PIR [passive infra red] body heat detector or a Ultrasonic detector.
I would expect it to be powered from the old controller, it could be any voltage. Again the output from the detector could be a switch.
[is there a model number on the detector?]

If the window switches check out as we expect, you could use a +5v supply with say, a series 470R resistor.
This would make the voltage compatable with either a PIC or PC [parallel port]

Lets know what you find so that we can suggest how to proceed.

Regards
EricG

 

[dinki]

The wires are all 'dead' so no need to be concerned about me getting a new electrified hair style

The next step is to do a continuity check like you suggested to map out the different zones. The wires already have a resistor soldered on the end but I'm not sure of the values. I'm guessing that the panel had 5V going out to the switches. That's indeed what I plan on using.

I don't have any ideas on what the motion detector might be. I guess I'll have to get up on a ladder and see if I can find a model number on the housing. Hopefully it will be either 5V or 12V.

I'm thinking that I'll tie one side of each zone's pair to +5V and then the other side would go to an individual pin on the PIC. I'll then output the value read by the PIC out to the PC via the Max232 . What kind of cpu usage should I expect on constantly reading the serial port? Will I need to throttle back the polling of the serial port to once a second?

 

[ericgibbs]

hi,

If you go the PIC route you could consider the PORTB as an common interrupt
for all the sensors, then test the other pins to see who is interrupting.

No need to poll all inputs.

Remember you will require zonal arm/disarm, exit and entry delays for arming.

If you get into the loft, [siren is there ???] check to see if got a name/label etc.

Eric

 

[dinki]

Great idea on the PORTB interrupt.

The arm/disarm will be handled by the computer via Mister House so no hardware bypass needs to be designed.

The siren is in the attic space somewhere. I'm thinking that once I isolate the window switch circuits then the siren will be one of two wires (the other being the motion detector). I'm thinking that I could try applying 5V to each and see if I hear the alarm. I'm pretty sure I know which is the end of the siren leads though. One of the pairs of wires has four wires with two each twisted together. Another has four wires with all four seperated. All other wires are two wires. I'm assuming that the two wires are the window switches, the four seperate wires is the motion sensor (??), and the four wire twisted into two is the siren. But of course this is all a guess at this point.

In short, I doubt I'll be able to get to the horn or even locate it without somehow sounding it.

 

[gerty]

Most alarm systems use a EOL (end of line) which a supervisory resistor on each loop. The value is typically between 2k and 3.3k, it's purpose is to indicate trouble if a wire is cut (if panel disarmed) and alarm if shorted out and panel armed. You might need to take that into consideration if you design a circuit, or simply remove them. They should be located in the last device on the loop. As far as the horn, it could be a self contained siren with the driver built into it in which case it'll probably draw 1 amp or better. The other option is that it's just a speaker and the driver was built into the main board. A simple ohm meter check will tell you this. A two tone siren, yelp for burg and steady for fire, will have 3 wires with the negative being common to both sounds.

 

[mramos1]

Well a 877A will do the trick for sure, but if you had loops or only a couple doors and windows it is overkill.

Interrupt are OK, put the PIC to sleep and let it wake up on the interrupt. But you must also check for keypad data, serial data and other things. Or is the PC the whole alarm?

But to be honest, I would poll it every 10, 20 60 seconds, check for serial data in that loop realtime and just run the PIC. The power saving is not worth it, code will be easier, and you have other thing to service like the serial data.

So how many wires do you have? Did you ohm them out and label the wires? Get that part done first. Come back with that for ideas on the chip and methods.

Also, I have to look, not sure if I used a MAX232 on mine. It is old and I forgot to bring it home. I either inverted the bits in software or used 2 transistors to fake the MAX232 (voltage level shifting). If you have a max232, then use it. But I doubt I had one as back then you need a bunch of CAPs for use it.


EDIT: Opps. Just caught the nine wires and 7 zones. OK, you do not need a 40 pin PIC. But your call. The 16F88 and an ICD2/Inchworm unit and you are set. And use the internal oscillator, less parts. Are you doing it in assembler?

 

[kchriste]

Any clue on how many volts/amps it takes to run the horn?

Usually they draw 1-2 amps.

Also, any clue on how the motion detector works and how to read it?

It'll just have 2 wires for power and two for dry contacts (simple switch). Usually if you open the back the PCB will have a terminal strip labeled with what's what.

 

[ericgibbs]

hi dinki,

A point which you should consider when you are wiring your PIC interface, is electrical noise.

Include some basic electrical noise filtering and transient suppression.

Flourescent lights can be a noise source, Local electrical storms can induce quite high voltage spikes, as you have long
unscreened cable runs.

The motion sensor probably has a connector or a coded terminal block inside its case, it may give you a clue to the wiring
back at the controller.

EricG

 

[mramos1]

The long wires do make great antennas. And will pick up lightning strikes as well. Maybe an MOV across them or isolate them.