Integration of Arduino with my alarm system board

Hi,
this is my first post here and my presentation. First of all, I apologize in advance for my bad English. I read other posts on this issue but I didn’t found what I need.

I am an experienced software programmer and I worked a lot on software-hardware interaction (developing device's drivers). Now I would like to have a deeper knowledge on electronics. So, an Arduino Uno board is coming :smiley:

After a learning period I would like to deal with a real and useful project. In my house I have a working anti-theft alarm system and I would to integrate it with some functionalities (i.e. monitoring inputs, arm/disarm the alarm system remotely, etc.) using the Arduino board.

This is the main terminal board of my alarm system controller:

  • SMU: alarm system status. +12V = ARMED, 0V = DISARMED. Currently not used.

  • IRK: a 1 second impulse to this pin arms the controller, another impulse disarms the controller. Currently not used.

  • CH1 - CH8 and GNDs: wired sensors +5V inputs:

  • CH1: magnetic contact switch (a passive door sensor)

  • CH2: magnetic contact switch (a passive door sensor)

  • CH3: signal from a powered PIR

  • CH4: signal from a powered PIR

  • CH5: magnetic contact switch (a passive door sensor)

  • CH6: magnetic contact switch (a passive door sensor)

  • CH7: signal from a powered PIR

  • CH8: signal from the tamper of the outdoor siren

  • RES: reserved

  • AUX: auxiliary power line 12V. Used by the outdoor siren and by the PIRs

  • JA: 1st alarm event output. Siren is connected here to COM and NO

  • JB: 2nd alarm event output. Currently not used.

These are my Arduino system requirements:

  • Read CH1-CH8 status
  • Read SMU status
  • Send a 1 sec impulse to IRK
  • Read the back-up battery charge status (a NI-MH - 12V - 600mAh, connected to a 2-pin header on the controller board). This is a very important requirement.

I think to put Arduino and other components needed in a box near to the alarm system controller.

I would like to receive some directions to connect the Arduino I/Os to the alarm system controller I/Os in a safe way. Which components I need? I have a limited space issue, so a compact solution is preferable.

Daniele.

This should be doable.
For monitoring 12V signals like SMU and battery voltage you will need to connect the voltage to the arduino through a voltage divider. A 18k and a 10K resistor will give you a 14V range and 14mV resolution on an analog input. The SMU cam be routed to a digital input through a similar divider. For the IRK pulse i would use a relay.
ch1..ch8 are 5V signals and can be read directly by an arduino (provided its a 5V board). If you need a small board have a look at the Nano, mini and micro boards.

nilton61:
[...]
ch1..ch8 are 5V signals and can be read directly by an arduino (provided its a 5V board).
[...]

Thank you for your answer niltron61, it looks less complicated than I guessed :slight_smile:

The alarm main board is powered by a 12V PSU and this is the voltage I measured (with a digital multimeter) for SMU, AUX, JA and JB signals. Indeed, the voltage measured for CH1-CH8 signals is 5V when the respective door is closed, 0 when is open.

Do you think that I can directly connect CH1-CH8 pins to Arduino digital inputs without any kind of protection?

There are a number of points to observe to give a thorough answer to that question:

  • The arduino can malfunction or be damaged if the incoming signals on ch1..ch8 exceed 5V. Putting in a series resistor can lessen this risk. You can put in an additional 5,1V zener to be really on the safe side

  • The arduino can interfere with the function of the alarm main board if any pins are set to outputs also this can be prevented by series resistors. If the resistance is higher than the resistance of the sensor the sensor signal will dominate.

Its a bit hard to give advice since i do not know all details of your circuit and you sensors.

nilton61:
There are a number of points to observe to give a thorough answer to that question:

  • The arduino can malfunction or be damaged if the incoming signals on ch1..ch8 exceed 5V. Putting in a series resistor can lessen this risk. You can put in an additional 5,1V zener to be really on the safe side
  • The arduino can interfere with the function of the alarm main board if any pins are set to outputs also this can be prevented by series resistors. If the resistance is higher than the resistance of the sensor the sensor signal will dominate.

Its a bit hard to give advice since i do not know all details of your circuit and you sensors.

Thank you nilton61 for your further advices.
To overcome the problem 2 may be an option to use a simple diode in series to the zener one?

its not that simple since the arduino can both sink and source current. But ensure all pins are input pins without pullup (this is the default configuration) and you will be fine

Ok, thank you very much.
I really appreciated your help.

Now I have more information from which to start working :slight_smile: