I have one question, about Arduinos (mine's Arduino Pro Mini), batteries and boost converters.
I was trying to read the battery voltage, and it was very accurate. I used a 100K-10Kohm voltage div. resistor pair, user the internal reference, used the VoltageReference library and the LowPower library for the ADC noise reduction mode. I also incorporated some concept using a calibration value from the secret voltmeter site-tutorial-something. My calculation for the calibration value is (battery multimeter reading/((raw analog reading*calibrated internal ref. value)/1024). I dunno, 1024 gives much more exact value than 1023.
Setting that aside, whenever I power the Arduino using the USB port and read thebattery voltage, the readings are accurate. However, if I use a boost converter from the battery to the Arduino, readings become awfully inaccurate, regardless if the Arduino is still powered by the USB or not (I dunno if powering the Arduino two way would be a good practice, but yeah making mistakes is my thing lol). One thing I also noticed the battery voltage drops from the original value (3.76 V to 3.50-3.30 V) when I connect the boost converter to it. Pulling the wire again, the battery reading bounces back to 3.76 V.
Is it just hopeless to get good results on this method of monitoring the battery voltage?
rayrayrayyourboat:
I dunno, 1024 gives much more exact value than 1023.
That's because 1024 is correct and 1023 is BS You do have 1024 steps
Pro Mini's / Nano's can be powered via programming header / USB and the Vin/RAW/5V/Vcc pin at the same time just fine.
But can you share a bit more details? Let's start off by a schematic (NO Fritzing breakboard mess!) and details on the converter. But (MCVE / SSCCE) code would be appreciated as well.
Here it is. These are the usual, cheap ones readily available here in our area, as well as the country. Haven't seen any circuit schematic about them, but they seem to bery handy. Only perhaps for simple applications
rayrayrayyourboat:
Setting that aside, whenever I power the Arduino using the USB port and read thebattery voltage, the readings are accurate. However, if I use a boost converter from the battery to the Arduino, readings become awfully inaccurate, regardless if the Arduino is still powered by the USB or not (I dunno if powering the Arduino two way would be a good practice, but yeah making mistakes is my thing lol). One thing I also noticed the battery voltage drops from the original value (3.76 V to 3.50-3.30 V) when I connect the boost converter to it. Pulling the wire again, the battery reading bounces back to 3.76 V.
Is it just hopeless to get good results on this method of monitoring the battery voltage?
Two things to tease out here. Firstly when you impose a load on a battery, its voltage will drop. How much
depends on the load and the internal resistance of the battery (which itself depends on the state of charge).
Secondly when you power the Arduino from a different supply, you will change the Vcc voltage itself, which
is the reference for analog measurements.
The Arduino automatically switches supply if you supply USB and Vin, I can't recall which has precedence, but
you can look this up, or measure the Vcc with a multimeter - that way you'll know if the measurement is real.
For best results with analog measurement you should be using the built-in linear regulator for the Arduino board
by feeding 7--12V to Vin or the barrel jack - that way the reference voltage is free of switch-mode supply noise and consistent for that Arduino across time (calibrate only once).
The ultimate would be to use a precision 4.096V reference chip to drive AREF pin and select
analogReference (EXTERNAL) in setup().
@MarkT, he said he's using the internal reference which would be a good thing. External ref can be even more precise but at least it's supply voltage independent.
On a Pro Mini / Nano there is no precedence. Vusb is just linked to Vcc via a diode. So as long as Vusb < Vsupply + 0,5V you're fine.
There's a good chance that the boost converter is drawing current from the battery in pulses (at the converter's switching frequency), causing the voltage to fluctuate rapidly. If you have scope, you might want to take a look at that.
If you don't have a scope, trying hanging a big (like 10,000uf or so) capacitor on the battery (observe polarity!) and see if your readings are still bad.
Here it is. I'm sorry I can't access my paper with the drawing on it. I'm somewhere else. But here it is in general.
I actually kind of messed up with my pic after editing it on my phone. Sorry. Hahahaha. The second pis a detailed view of my simple power state detection (checks USB that powers the TP4056 has current, if yes, normal power conditions. Otherwise if cord is removed or no power is present, power interruption). Readings are also weird if I charge the battery while reading it with the said circuit. As soon as I get my hands on a scope and have my multimeter fuses replaced, I'd be so glad to work this out day and night.
Okay, I promise to draw my schematic all over again this time. I'll upload them later. Thank you for going this far.
I was trying an RC filter of different combinations on the analog pin which checks the battery voltage and the boost converter output. Nothing good still comes out. Hahahaha. I'll be looking for extra help too but if you have more to say, please do. I'd appreciate it.
I've also noticed that when the Arduino Pro Mini is powered via USB (using USB to UART adapter) it reads battery voltage accurately and battery voltage is around 3.74.
However, when I connect the battery to the booster to power the Pro Mini which reads battery voltage, the multimeter reads an instantaneous decrease in voltage at around 3.50-3.40 V. I know the water pressure analogy and some like the ESR which produces this phenomenon, but how is voltage monitoring going to be possible with these issues at hand? It seems like checking the voltage of the battery accurately is impossible unless you don't connect any load to it.
Okay, I'll try to reduce my voltage divider values from 100K-10K to 10K-1K for the 1.1 V voltage reference at the pin. But isn't that going to consume a lot more current?
I dunno if this is cray cray or pathetic, but is it possible to use a transistor to control when will voltage and current flow into the voltage divider when I'm going to perform an analog read? Like this:
Digital write high to transistor base (with base resistor)
Analog read at voltage divider connected at collector.
Okay, I'll try to reduce my voltage divider values from 100K-10K to 10K-1K for the 1.1 V voltage reference at the pin. But isn't that going to consume a lot more current?
I may be a little late to the game ( I only see ?? for the dates).
It is absolutely possible to get a good reading in a noisy environment. It is common to read millivolt thermocouples it such an environment. The suggested filtering should work, you must keep the divider and capacitors near the arduino input.
@Perehama
Okay. I'll try and do as what you suggested. Perhaps I'll be needing to rearrange all the components on a seemingly small breadboard. Again.
@JohnRob
No there's no USB input. What I meant was, I used a USB to UART adapter that has male pins. I connected female-female jumper pins to connect it with the Arduino Pro Mini's uhh FTDI header pins.
rayrayrayyourboat:
I used a 100K-10Kohm voltage div. resistor pair, user the internal reference, used the VoltageReference library and the LowPower library for the ADC noise reduction mode.
I also incorporated some concept using a calibration value from the secret voltmeter site-tutorial-something. My calculation for the calibration value is (battery multimeter reading/((raw analog reading*calibrated internal ref. value)/1024). I dunno, 1024 gives much more exact value than 1023.
100k:10k is for voltages up to 11volt (with 1.1volt Aref).
Not very good for measuring a 4.2volt LiPo battery (I think you're measuring a single LiPo).
With that ratio you loose more than one bit (measuring with <= 9bits resolution).
Pick a ratio that is close to 3.2:1, like 100k:33k (= 1.042volt out at 4.2volt in).
No need to use libraries. Converting A/D value to voltage is only one line of code.
float voltage = analogRead(A0) * 0.0042317; // calibrate by changing the last digit(s)
Nooo. secret voltmeter is for measuring VCC against 1.1volt Aref.
When you switch to 1.1volt Aref, VCC is out of the picture.
Adding that could make the result depedent on VCC of the Arduino again.
Leo..
You do have 1024 steps 
