Community wireless mesh sensor/control network

Quick update on what we are up to these days.

We are working towards rolling out a WiSense low power wireless sensing/control network in Pruksa Silvana (east Bangalore) where I live. This is a new community of around 400 houses out of which around 150 are currently occupied. The idea is to use this network to provide wireless sensing and/or control throughout the community. The network will initially have a single WiSense coordinator/gateway node, multiple FFDs (full function devices which will be involved in routing) and multiple RFDs (energy constrained nodes). We are currently testing solar powered FFDs since these nodes will be installed outdoors. These nodes will have a small solar panel (max 3 Watts) charging an NiMH battery pack. This will provide enough energy to keep an FFD powered up 25/7. These FFDs will not have any sensors. Assuming an average current consumption of 25 mA, the energy usage per day comes out to 25/1000 * 3 * 86400  = 6480 joules. A 3 Watt solar panel will produce around 3 * 3600 * 3 = 32400 joules per day assuming just 3 hours of good sunlight. This is ok since we want the node to tide through a week of bad weather. The battery pack currently has three 2500 mAH NiMH cells with best case capacity of 2.5 * 1.2 * 3600 = 10800 joules.

We are going to introduce a “lite” version of our eval module suitable for routing only nodes (FFDs without sensors).  Just got the bare PCBs today so I will share some pics in another day or two. This version does not have any sensors. It also does not have a USB interface. It has two boards. One is the radio board and the other is the micro-controller board. The latter has a 128 kilo-byte eeprom to support over the air firmware upgrade.

Coming back to the solar powered node, the battery pack voltage is being monitored by a voltage monitor IC. When the battery pack voltage drops below 2.7 volts, the monitor IC shuts off a load switch which is gating power to the node. When battery pack voltage climbs above 2.8 volts, the load switch is turned on. The MSP430 on the node powers on and it monitors the battery pack voltage until it climbs above 3.9 volts at which point the radio is switched on and the FFD starts operating normally. These thresholds will likely change before we are done with testing this (solar + batt) power source. We are streaming the battery pack voltage (being reported by the solar powered FFD every 10 seconds) to Xively (channel id is V_sony_batt).

Here is a pic of the solar powered FFD on the terrace. solar_ffd

Posted on March 29, 2015, in Uncategorized. Bookmark the permalink. Leave a comment.

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