Authentication unit over radio

Recently new user of OHS gateway has explored a slightly new way how use authentication units. That is normally until now, the authentication units are desired to be online when main unit is online. This was easily achieved when they were wired nodes with RS485 wired connection. The power and data were going to node over 4 wires, like in any industrial RS485 application. Same 4, or more, wires are usually installed in your house for old authentication units. And it is easy to use them switching old unit to new one.

But what to do in case you have no wires in walls and you want try it without too much construction work. Well, then use the radio as for sensors, right!.

For this reason there is new code example on GitHub. The code is build on RFM69 example, but adds parts of wired node where iButton, LEDs and speaker is used to complete a basic authentication node. I have tested it and it woks quite well without any issue. There were some changes needed in the gateway code, and I will soon post them to GitHub as version 1.7.6.3, along with other tweaks.

Of course there are some drawback over wired connection. It is recommended to have some battery backup for the node as well. That is use the USB node with charging and place a decent 1000mAh, or better bigger, battery. Still it can happen that the gateway is powered from it main 12V supply, and the authentication node battery is depleted and dies. In this case, when you arrive at home at this exact moment, you will not be able to disarm standard way, and you will face system alarm. It is probably not a security concern, but you'll annoy your neighbors a bit until you run to your gateway and turn it off. Thankfully there are two possible solutions. There is possibility to disarm over web interface, but unless you have battery backuped home network, you probably will not be able to do so. But, you can always disarm group over SMS command, this should work as GSM module is in the gateway.

Second problem can be radio connection. As for any sensor, the radio authentication can be out of reach of the gateway. While it is unlikely in normal house, you have to think about having at least RSSI of -75, so you are guaranteed to have room to some unexpected radio noise. It can be easily checked in web interface debug tab, incoming RSSI is reported on any received node packet.

Also, one have to keep the unit powered all the time from at least 500mA USB charger, some older cellular charger perhaps. As the node is not entering any sleep state, nor suspending the radio module, and consuming 20-40mA of power. It cannot be asleep, as it needs listen to receive all radio updates. Rest of power to 500mA is to charge the battery after power failure.

Still I think these small disadvantages can be accepted as trade off for fast deployment.