I am testing sensor node with Arduino.
The setup is Temperature sensor + Arduinoboard + Battery + Solar panel + Xbee for wireless transmission. It is placed on outside home. (hot weather).
The sensor node is using 3.7V /6600mAh battery with Arduino (Seeeduino;it is based on Arduino).The battery charged with Solar panel. I am reading Analog Pin 7 for battery value to calculate battery %. Think it is 8bit ADC resolution.(0 to 256).
Generally, I noticed, the battery percentage curve goes higher before it dies. Like 10 to 12 hours before it dies. i.e battery decrease Usually, if the Sun light is good, it last for many days.
If not, the battery decrease gradually and become low... and increase suddenly for few hours and stop completely. When measure the voltage of that dead battery ; it around 2.8v.
I am not sure, why this sudden increase happens ? Is it because of Lipo battery or Arduino (Seeeduino) reference voltage is not accurate when battery is low.. I am using Analog Ref.Voltag is 3.3v (default)
Yes, your reference voltage is dropping when the battery drops. This is a tricky problem and
you would actually be better using the internal reference which won't droop. Note the internal
reference voltage varies a bit from chip to chip so you have to calibrate it.
Thanks for your reply. It is nice to some one thought. Yes, i too think, it issue with AREF voltage.
When i use AREF Internal 1.1v; some issue with sensor operating at 5v. I'm using few 5v sensors.
Using Voltage Booster, supplying the 5v or higher voltage to sensor from Seeeduino board 3.3v.
So, when i use Internal AREF , noticed some sensor giving high values. So, now using Defalut AREF. So, far no major issue.
Which temp sensor are you using.
LM35/36 have ~100 degrees range when measured with 1.1volt Aref.
The LM35 = ~+5 to +105 degrees C
The Lm36 = ~-45 to +55 degrees C
Some (TMP35/36) work from a 2.7volt min. supply.