Arduino Two-Sensor Temperature Logger

Abstract

Temperature Logger was built to track changes in temperature over time. Two different sensors detect temperature, display shows it to the user, SD-card is used to store historic data.

Problem

The goal was to measure room temperature and an impact of the building’s heating system. To accomplish this, I needed a thermometer with two sensors. One would measure room temperature, the other would detect if the radiators were working or not. The data would be recorded on an SD-card for post-analysis.

Solution

Solution consists of:
* Arduino Uno
* Temperature sensors: thermistor and LM35 (similar to TMP35 and TMP36)
* SD card reader/writer
* LCD display: 20×2

Photos of the Temperature Logger

Temperature Logger LCD
Temperature Logger LCD

Temperature Logger Top View
Temperature Logger Top View

Output Log File

557668,12:43:13 07/02/2014,F,68.95,C,20.53,TC,56.05,TF,132.90
557698,12:43:43 07/02/2014,F,68.95,C,20.53,TC,57.88,TF,136.18
557728,12:44:13 07/02/2014,F,68.77,C,20.43,TC,61.80,TF,143.25
557759,12:44:43 07/02/2014,F,68.95,C,20.53,TC,59.01,TF,138.22
557789,12:45:13 07/02/2014,F,68.77,C,20.43,TC,55.33,TF,131.60
557819,12:45:43 07/02/2014,F,68.77,C,20.43,TC,57.88,TF,136.18
557849,12:46:14 07/02/2014,F,69.13,C,20.63,TC,51.27,TF,124.28
557879,12:46:44 07/02/2014,F,68.95,C,20.53,TC,51.15,TF,124.07
557909,12:47:14 07/02/2014,F,68.77,C,20.43,TC,51.88,TF,125.38
557939,12:47:44 07/02/2014,F,68.77,C,20.43,TC,50.91,TF,123.64
557970,12:48:14 07/02/2014,F,68.95,C,20.53,TC,56.95,TF,134.51
558000,12:48:44 07/02/2014,F,68.95,C,20.53,TC,55.19,TF,131.34
558030,12:49:14 07/02/2014,F,68.95,C,20.53,TC,56.20,TF,133.16
558060,12:49:45 07/02/2014,F,68.95,C,20.53,TC,50.55,TF,123.00

Format:
Time since start, GMT Time/Date, Temperature-1 in F, Temperature-1 in Celsius, Temperature 2 in Celsius, Temperature 2 in Fahrenheit

Resulting Temperature Graph

Temperature Graph
Temperature Graph

Application Source Code

More information

  • Original design called for battery-operated sensor. However, with 42mA power consumption even during sleep, this proved impossible (9V battery lasts for 1.5 days). This link illuminates the source of the problem and ways to solve it –
  • SD Card Reader bought at RadioShack for about $10. The SD Card reader is used with SDFat arduino library.
  • Two different kinds of temperature sensors were used LM35 and Thermistor. Thermistor required special considerations for calibrating Resistance->Temperature mapping. I found two methods for the calibration:Steinhart-Hart model and B-model).
  • Source code

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