3.7V Lipo battery behaviour

Dear All,

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)

Appreciate your answers /thoughts. Thanks. :slight_smile:

Cheers!
chandra

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.

Hi Mark T,

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.

Any thoughts? :slight_smile:

Cheers!
Chandra

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.
Leo..

Hi,

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Can you please post a copy of your sketch, using code tags?
Please use code tags.. See section 7 http://forum.arduino.cc/index.php/topic,148850.0.html

Thanks...Tom...... :slight_smile:

For temp. and Humidity sensor I am using Dfrobot SHT1x . It is not giving any error when AREF is 1.1v. Think it is because of digital.

circuit is below:

But analog sound sensor, (Dfrobot one) gives high value when when AREF 1.1.
Circuit:

@Tom: I did not want to post code and make it complex. Issue is ARFE not correct..when voltage below 3.3v. On the code I did not declare AREF,so it default.

Thanks!
Chandra