Update on the live feed from WiSense node

I let the sensor node send data to xively for a couple of days and noticed a couple of unexpected trends in the data. One was the drop in battery voltage during the night and subsequent rise in the morning. We expect the voltage to keep dropping as the battery discharges but the data showed a rise in voltage of around 0.2 to 0.3 volts. One explanation can be the  rise in the battery’s internal resistance with drop in ambient temperature.  The other trend was abnormally high temperature reading from the MSP430’s on board temperature sensor. The sensor was reporting around 40 degree celcius around noon. I moved the node around and saw the temperature drop and then climb back to more than 40 degree celcius. Surprisingly, the sensor was tracking the night time temperature well.

I replaced the Maxell coin cell  with a Sony coin cell. I also interfaced an external temperature sensor (TMP102) to the sensor node. This is a high accuracy (0.5 deg C) sensor with I2C interface. The sensor has a current consumption of less than 1 micro-amps in shutdown mode. The sensor stays mostly in shut down. Every 5 seconds, the app layer on the RFD node triggers a single temperature conversion during which the TMP102’s power consumption increases to around 10 micro-amps. The conversion takes around 26 milli-seconds after which the TMP102 goes back to shut-down mode. The node is now reporting the TMP102’s data to Xively.

I also measured the sensor node’s current consumption . It  is around 1.2 micro amps when the micro (MSP430), the radio (cc2520) and the temperature sensor (TMP102) are all in low power mode.  The node is sending data to the coodinator/gateway once every 5 seconds.

Snapshot of data streamed to Xively.com

xively_snapshot

Posted on December 30, 2013, in Uncategorized. Bookmark the permalink. 1 Comment.

  1. if it can be so sensitive to temperature variations
    wireless sensors can be used in cryo freezers and incubators especially on moving tanks
    or containers on conveyors /or on castors in food industries,pharma industries ,fish packing etc to monitor and control

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