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I am using 3 AA batteries of 1.5V each, to obtain a voltage of 4.5V which i am then reducing to 3.3V using a LDO. My current requirement is around 100mA.

I want a simple, low power dissipation circuit which would be connected to the arduino to monitor this battery level

Previously for one of my projects I have used a simple zener diode to monitor the battery level. However I didn't take into account the heat dissipation, reliability etc.

So, can I know what are the different types of options available? My main constraints are:- 1)Circuit should be simple 2)Low power dissipation

I am attaching the pics of my entire circuit and the zener circuit which i used before.Entire Circuit[![][1]]2

To provide a bit of background of the zener circuit, I first calibrate it for my application, then I am able to view the percentage of battery at the display.

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  • \$\begingroup\$ LD is reversed. If Arduino runs on 5V you can read LED-battery voltage with ANALOGIN function. Why not use Arrduino supply for LEDs? Alkaline cells range from 1.65V/cell down to 1V when exhausted. LDO will drop out at low end. \$\endgroup\$
    – Russell McMahon
    Apr 11, 2020 at 7:26
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    \$\begingroup\$ Is there any chance you can rotate the image correctly? You will get a lot more readers. \$\endgroup\$
    – Transistor
    Apr 11, 2020 at 8:23
  • \$\begingroup\$ Many questions in here about this, just one: electronics.stackexchange.com/q/19355/152903 \$\endgroup\$
    – Solar Mike
    Apr 11, 2020 at 8:56
  • \$\begingroup\$ @RussellMcMahon LD is a zener. it is oriented correctly. \$\endgroup\$
    – Jasen
    Apr 11, 2020 at 9:06
  • \$\begingroup\$ It's actually a zener diode not a LED @ Russell McMahon \$\endgroup\$ Apr 11, 2020 at 14:27

2 Answers 2

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setting the GPIO high turns on Q1 and Q2 presenting half the battery voltage to the analog input.

setting the GPIO it low turns off Q1 and Q2 avoiding unneeded drain on the battery.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ I am a bit confused, will this circuit help me in displaying the battery level status in the arduino or does it act like a level detector? \$\endgroup\$ Apr 11, 2020 at 14:31
  • \$\begingroup\$ it sends a representation of the battery level to the arduino on request. \$\endgroup\$
    – Jasen
    Apr 11, 2020 at 19:23
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    \$\begingroup\$ You likely need one more resistor, from base of Q1 to its emitter. \$\endgroup\$ Apr 13, 2020 at 2:42
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    \$\begingroup\$ modern transirors have very low leakage but that wouldn't hurt added R5 \$\endgroup\$
    – Jasen
    Apr 13, 2020 at 4:15
  • \$\begingroup\$ Thanks a lot Jasen , simulated the circuit also, one final doubt since my transistor is basically acting like a switch can i use any transistor model or are there any constraints? \$\endgroup\$ May 3, 2020 at 14:40
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You can use a simple voltage divider, with an optional voltage follower/buffer opamp (A lot of low power options are available).

schematic

simulate this circuit – Schematic created using CircuitLab

The opamp and Zener are optional but are good design considerations. Especially the opamp will reduce the source impedance of the reference voltage. (as recommended by Arduino for its ADC).

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