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From our previous post, we made a small number of changes and started building acrylic cases/mounts for some of our boards. This time the cases/mounts have been build, a few more smaller changes and add in the SMS capability.


Here’s how everything looks at the moment – ready for deployment. I’ve got cases for the PIR, door sensors and the alarm system server which I’m planning to mount to the wall, connect the leads to the battery/adapter on the ground and the siren near the ceiling.


One problem that I’ve been able to find a simple solution to is how to mount the PIR on the corner of the wall like my current alarm system does. I’ve found that a 0.5mm aluminum sheet is flexible enough to cut with tin snips, mold into a U shape and it will keep it’s shape.


Another use for the aluminum sheet has been to make a custom heatsink for the LM317T which was getting a bit hot as the 12V battery hadn’t been charged in some time. I didn’t have long enough screws to hold the case together so that I can easily take it apart if I need to reprogram the MCU, so I used brass spacers to extend the screw.

In terms of a case for the remote, I’m thinking against a case and instead just putting a layer of glue all around it so that we keep the size down. For the SMS side, I can pretty much  re-use the code I’ve had previously in the AlarmSM SMS Sender and modify it to suit the ATmega328 and to send an SMS to two recipients. Download AlarmSM_v2.2

I’ve been running the PIRs and door sensors for a few days without any issues so I think I’m ready to wrap this project up and make it all live.

Some improvements in the future or if I were to re-design it all they would include:

  • Adding a button that will only activate the door sensors which would be useful when heading off to bed, so if a door is opened when I’m in the house a quieter alarm will only go off in my room
  • Spacing out the board layouts a bit more, leaving more room around the voltage regulators, pin headers and capacitors
  • Change the alarm server to use a SMPS instead of the LM317T
  • Add in the battery holder to the door sensor PCB
  • Use RSA or equivalent as authentication of the server by the sensor and then give a sensor it’s own rolling code or possibly look into the Atmel CryptoAuthentication or equivalent as if a sensor is taken it can be used to gain access to the system; though at this point in time it’s not a concern for me

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