WSN: Temperature Sensor

The temperature sensor is based on the TMP36 Low Voltage Temperature Sensors.

My first attempt at creating a wireless temperature sensor was using a TMP36 device from Analog.  The TMP36 looks like a transistor because it is in a TO-92 package.

I soldered together an XBee Adapter board from Adafruit then I soldered the TMP36 directly to the adapter board.  Using the layout above. I soldered the voltage input pin to the closest VCC trace, the ground to ground (obviouisly) and the Analog Voltage output pin to the AD0 pin.

TMP36 on the XBee adapter

TMP36 on the XBee adapter

This seems to work fairly well if you only have one input.  If you plan to use multiple sensors on the XBee ADC inputs, you’ll need to set up a rail to rail op amp buffer.  But that’s for another post.








Here’s a live sample of a TMP36 data stream from my back porch as derived from a chart on

Large spikes are a known problem with the data collection downstream of the TMP36 and the XBee module.  To be fixed soon, I hope.


Next Post: Gas Sensor
Next Group: Radio:XBee


WSN: Tweet-a-Watt

The Tweet-a-Watt is a wireless power meter based on a commercial device called the Kill A Watt which is hacked to include a wireless XBee radio.  It was designed by Limor Fried of Adafruit Industries and she has written up one of the best online tutorials for a kit based project.  It collects data from the Kill A Watt from P3 International and with an added XBee radio sends data to a PC and then on to a twitter feed.  Hence the name, Tweet-a-Watt, a combination of Twitter’s Tweet and the Kill A Watt power meter.

You can build a Tweet-a-Watt by following the tutorial here.

The basic components:

Kill A Watt Power Meter (P4400)


Everyone should own at least one Kill A Watt.  It can tell you the cumulated kilowatt hours (KWh) at the plug load of an appliance, along with the volts, amps, and watts.

With pencil and paper and a little time you can hook this up to the various appliances in your home and look at the meter and simply “do the math”.  With the math, and perhaps a spreadsheet program, you can analyse what your appliances draw in watts and learn what to turn off or use less.  You can get them online for as little as $17 and at your local hardware store for about $25.
XBee Radio
The Kill-a-Watt starts to become a Tweet-a-Watt with the introduction of an XBee radio.  The radio can be hooked up inside the Kill-a-watt and that makes it possible to transmit the readings from the Kill A Watt and send them to a computer for logging and analysis.

The original design of the Tweet-a-Watt project had an XBee radio receiver hooked up to a PC through what is known as an FTDI USB cable; essentially a serial input.  There was a python script that would run on the PC and collect the serial input and  package the data for delivery to a twitter feed.

During my investigations I saw Limor Fried’s short video about using an Asus Wifi Router instead of a PC to collect and send the sensor data to the internet.  If you’re trying to reduce your energy consumption it seems a shame to have to run a PC; even a laptop will draw perhaps 60-90 watts.  The Asus wifi router setup can be configured to run the python script and do the same basic job as the PC but it only draws about 4 watts.  Much better.   See the post about setting up the ASUS WL-520gU.

Next Post: Temperature Sensor
Next Group: Radio XBee