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‎02-26-2017 11:49 PM

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I have a project, using a temperature sensor, TMP36 and Arduino. Basically its a bluetooth thermometer. Everything worked fine at breadboard and connected and energized by my notebook. Now I connected it to a 4 x AA recharchable batteries and I started to get wrong temperatures (running on USB, I get 22 degrees, running on batteries, I get 44 degrees).

As formula to get the temperature, I'm using this one:

Temp in °C=Vout(in mV)−50010Temp in °C=Vout(in mV)−50010

My debug info follows:

UPDATE

  1. USB (5v)

voltage read from TMP36 = 147

voltage converted to 5v arduino

(147 * 5.0) / 1024  = 0.71temperature = (0.71 - 0.5) * 100 = 21.78
  1. Battery

4 x reachargable AA = 1.2v (voltimeter says 5.6v) not enough energy to turn it on the BT module, but the board was turned on (power light was on)

  1. Recharged Battery

4 x reachargable AA = 1.2v (voltimeter says 6v.7)

voltage read from TMP36 = 171 voltage converted to 5v (I assume, that the arduino has a voltage regulator to limit the input to 5v, right?)

171 * 5.0 / 1024 = 0.83 
temperature = (0.83 - 0.5) * 100 = 33

my questions are:

  • Is there a way to correct it via software or should I drop the voltage, using a diode/resistor?

  • At the datasheet its written that the input voltage range is from 7v to 23v. Does it means that it has a regulator to 5v internally to regulate my arduino to 5.5v? Does it means as well that I will need more battery to put it to work?

Arduino used is the Iteaduino BT

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