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 Pachube.com:

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

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  1. #1 by Jim Dodgen on 07/26/2011 - 11:19 am

    what is the issue with the xbee and multiple adc inputs? I ask because I am getting unusual readings from the tmp36, things seem to float around +- 3 Degrees C every few seconds.

  2. #2 by Chris Jefferies on 08/11/2011 - 8:58 pm

    In general the readings of the TMP36 have been fairly solid. The issue I was seeing was between the various pins; like 19, 20. I would see some drift in one when the values in the other would go up or down. I did some research; asked around on some forums and came to the conclusion based on the advice I got that I should include an op-amp between the analog output and the xbee analog input. I used a TI TLC 2274 IN quad op amp.

    • #3 by Jim Dodgen on 08/14/2011 - 4:30 pm

      thanks for the reply, I think my problem was mostly the length of the cable that I had the TMP36 attached as well as a poor quality power source.

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