It has been more than a year as a hobby I have been making Environment Zigbee sensor. I will not bore everyone here since there are already long discussion about it here.
I thought since we are able to monitor environment aspect of a room lets look at some other thing that probably make sense to monitor. In a way, I am always looking for a way to extend the modules.
Here is what I come up with. I added an AC to DC power converter so that we do not need to use our old USB phone charger. My thinking when I started doing this, I want to get more value out of adding this power converter. After all, we all should have access to old un-used USB charger. I do not want to replicate this model. I am looking to use the converter to patch power from my home hardwire smoke detector. They are powered by AC voltage. My thought, by this time, is that I may as well try to connect to the interconnect wire to get notification when the smoke detector detect some activity.
I have to credit Dr Edward Cheung for his work here for the interconnection research. The interconnect signal has evolve since then. In addition, Its extension may be different between vendors. I extend the idea to solve supporting additional device in the line is by sampling the line and report result of that sampling value. We know when the value of the line is the same after some period, they either say that there is no activity or there is smoke detected. The legacy signal sampling is simple. When there is a smoke, a constant 9v signal is sent on the wire. Any newer signals are a bunch of pulses of high (one) or low( zero). They may form a code when you decode them to a 8 bit variable. I am packing these bits to the extended zone status in IAS Zigbee cluster.
Based on my reading on Dr. Edward Cheung's work, his idea to connect to the interconnect wire is safe. The circuitry does not drive the line. It just listen to it.
I also added small circuit to detect power outage. This leverage the battery backup in the module that I have been developing.
Here is some demo of the project. I am sorry the video is on the longer side. I am looking to trim them down. In the meantime, I am excited to share what I have been able to get with it.
If there are any interest among pioneer, I should have a few boards more than I need myself to share like in my other project. However, I want to tide some things here and there before I would do that. I will wired it to my home smoke detector system to make sure that I am the first user.