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Topic: Low Battery Monitoring for LiPo (Read 10487 times) previous topic - next topic

retrolefty

1. When you say Counts, you mean the reading returned by the Arduino, right?

Correct, values are a 10 bit binary result of the analogRead() command and can range from 0 =0vdc input to 1023 = 5vdc input.
1. If I use a 10k Resistor, will there be a voltage drop I have to take into account?

No there will be no voltage drop due to the very high input resistance of the analog input pin. However there will be possible conversion timing problems with using such a resistor. No resistor is required for wiring the 3.7vdc battery voltage directly to the analog input pin.

3. I am also using a external AREF connected directly to the 5v supply line, will I have to change any calculations due to this?

Why are you using the AREF pin? By default the arduino uses the Avcc voltage (+5vdc in your case) as the reference already so wiring your 5vdc supply to the AREF pin and using the external reference is redundant and not required.

Lefty


drbogger

So would you recommend wiring it without a resistor? or with one?

I always thought the AREF was something like 1.1v by default... and I wired it to 5v because I have a couple temp sensors, and some other analog devices hooked up to it... Plus the circuit board is already designed and made, so I have to use what is already existing... Unless I cut the trace, which I'd rather not do... lol

retrolefty


So would you recommend wiring it without a resistor? or with one?

Without one.
I always thought the AREF was something like 1.1v by default...

AREF is a name for a pin that one one can input a voltage to and allow it to be the reference voltage to use with analogRead commands if you set the reference to external. The default is to use the same voltage that is powering the chip, +5vdc in your case. So just leave the Aref pin unconnected.

and I wired it to 5v because I have a couple temp sensors, and some other analog devices hooked up to it... Plus the circuit board is already designed and made, so I have to use what is already existing... Unless I cut the trace, which I'd rather not do... lol

In that case you will have to use the external reference command and set the reference to external. Nothing gained, just redundant in design.

Lefty


drbogger

Would you recommend the use of a filter capacitor?

sdturner

I recommend a series resistor, but it is not necessary. There will not be any significant voltage drop. IIRC the input resistance for an analog pin is 10M Ohms. I don't remember if that is typical or minimum, but either way there will be much less than 1uA of leakage current.

You probably won't need a filter capacitor, but if you get a lot of noise in the voltage reading you can add it later. If you have no resistor, then the capacitor won't do much of anything.

SInce you will not have a resistor divider, you should use Vbatt = 5 * Counts / 1023 to convert the analog reading (counts) to battery voltage.

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