================== W A R N I N G ! ! =================
Li-Ion batteries are very dangerous if not handled properly.
Use them only with proper protection circuits and chargers.
Using any of the informations available on esp8266-projects.com
 is on your own risk !!

     For any new CBDBv2 Evo orders/requests please feel free to use as usual:
     tech at esp8266-projects.com.
If you want for your own experiments to order CBD v2 EVO bare PCBs only, you can also do it directly at Dirty PCBs, our preferred PCB House:



One of the main problem in battery powered projects is to choose/use the proper battery size/model/type. As market is flooded now with a lot of low quality batteries claiming thousands of mAh ( Ultrafire fakes stories is just an example) the only way to proper check them is to run a set of tests.

A simple basic capacity test / loading / discharging time values can give you valuable informations about the parameters and health of the battery. And of course also you can see how are looking the numbers against the datasheet claims :).

Few general considerations that I want to bring to your attention:

  • The capacity of a battery tells you how much charge it can store.  This means that they can theoretically provide a current of 2A for one hour, 1A for two hours, or 200mA for ten hours. In reality a 2,000mAh battery would not provide 20mA for 100 hours, nor 2A for one hour.
  • Discharge load –  this is a tricky one and most of the time not clear explained by battery manufacturers in their datasheets. Mostly of them are using a discharge load of 0.1C, that means one-tenth of current capacity when rating their batteries. Therefore, a battery which can provide 200mA for 10 hours would be rated at 10×200 = 2,000mAh !!

         A faster discharge rate would result in less energy being extracted from the battery, and
therefore the measured capacity would be lower. If you are using batteries in energy-hungry
devices that need more than 0.1C, the real capacity will be lower than that published.

A “good-to-have” add-in for a battery powered project is a system that will be able to monitor over the entire battery lifetime at least few parameters like, voltage, current, power consumption and stored energy between charges.

   What we will need:


As the CBDBv2 Evo DevBoard has already Voltage and Current measurements capabilities onboard, the only thing that we will need to do is to connect the battery module that we want to measure to the board:

BLUE    –  GND
RED      –  SH_IN+

By default the CBDBv2 Evo Board comes prepared for Li-Ion batteries voltage range, with the onboard default voltage divider values and Rshunt you have VmaxIN=4.3V and ImaxIN = 1A. If you need a different Voltage/Current range just change/ask for different default values.

CBDB v2 Evolution DevBoard with INA21x Current monitor

    The Current shunt monitor used for this project is a INA21x family one. 

The INA210, INA211, INA212, INA213, INA214, and  INA215 are voltage-output, current-shunt monitors that can sense drops across shunts at common-mode voltages from –0.3 V to 26 V, independent of the supply voltage. 

    Five fixed gains are available: 50 V/V, 75 V/V, 100 V/V, 200 V/V, 500 V/V, or 1000 V/V. 
    The low offset of the zero-drift architecture enables current sensing with maximum drops across the shunt as low as 10-mV full-scale.

   These devices operate from a single 2.7-V to 26-V power supply, drawing a maximum of 100 μA of supply current. All versions are specified over the extended operating temperature range (–40°C to 125°C), and offered in an SC70 package. The INA210, INA213, and INA214 are also offered in a thin UQFN package.

 INA21x Features:

• Wide Common-Mode Range: –0.3 V to 26 V
• Offset Voltage: ±35 μV (Max, INA210) (Enables Shunt Drops of 10-mV Full-Scale)
• Accuracy:
– ±1% Gain Error (Max over Temperature)
– 0.5-μV/°C Offset Drift (Max)
– 10-ppm/°C Gain Drift (Max)
• Choice of Gains:
– INA210: 200 V/V
– INA211: 500 V/V
– INA212: 1000 V/V
– INA213: 50 V/V
– INA214: 100 V/V
• Quiescent Current: 100 μA (max)

     For any new CBDBv2 Evo orders/requests please feel free to use as usual: tech at esp8266-projects.com.
If you want for your own experiments to order CBDBv2 EVO bare PCBs only, you can also do it directly at the PCB House:  


For that ones of you that want to use a different Board or just want to add these functions to a ESP8266 Module, you just need:

  • for Voltage –  add and size on your needs the voltage divider as explained in details in the previous article about ESP8266 Internal ADC.
  • for Current – add your favourite Current Monitor but don’t forget about the VmaxIN for ESP8266 ADC of about 1V!

   BLMS Software
  For programming CBDBv2 Board and uploading the drivers and the software we will continue to use the LuaUploader as before.

   How to Measure Battery Capacity

   When measuring the real battery capacity what we are interested in is the amount of energy stored in a battery since it is this energy we need to power our devices. Stored energy is measured in Watt-hours – the same unit used to measure our domestic electricity consumption (where 1,000Wh = 1kWh = 1 unit of electricity).

In order to measure the stored energy in a battery a power resistor is used as the load, and a fully charged battery is fully discharged through it. By measuring the voltage across this resistor at regular intervals during the discharge process it is simple to calcuate the total energy dissipated and therefore the total energy which had been stored in the battery.

Using Ohm’s Law (I=U/R) we can then calculate the current flowing through the load since we know the voltage across it. Instantaneous power is given by multiplying the measured voltage by the calculated current (P=U*I).

By taking readings for a certain amount of time until the battery is completely discharged, and adding up the energy dissipated in each time interval, we can calculate the total energy taken from the battery and dissipated in the resistor and therefore the total energy that was stored in the fully charged battery.

Software Implementation
1. Define used GPIO pins and variables:

ADC_SRC = 5                                       -- GPIO14 - select Voltage Divider / Current Input
sda=2                                             -- GPIO4  - SDA
scl=1                                             -- GPIO5  - SCL 
gpio.mode(ADC_SRC,gpio.OUTPUT, gpio.PULLUP)
gpio.write(ADC_SRC,1)      -- Voltage Measurement - Voltage Divider Source selected
gpio.write(ADC_SRC,0)      -- Current Measurement - Current Shunt Monitor output selected
voltdiv= 0.00412                                 -- Voltage reading calibration
dival = 0.00096                                  -- ADC volt/div value - CALIBRATE !!  
resdiv = 4.31447                                 -- Voltage Divider Ratio - CALIBRATE!! 
divalI = 0.9425                                  -- Current volt/div ratio - CALIBRATE!!
cpct = 0                                         -- Calculated Delivered Energy
adcI = 0                                         -- ADC readings -  Curent
adcV = 0                                         -- ADC readings - Voltage
pwr = 0                                          -- Calculate Power
t=0                                              -- time   

2. READ ADC – Voltage  

function readADC_Voltage()
      adcV = 0
      advr = 0 
      print("\nADCV Step   : " ..string.format("%g",advr).." steps")
      print("Voltage     : " ..string.format("%g",adcV).." V")
      return adcV

2. READ ADC – Current

function readADC_Current()
      adcI = 0
      adcr = 0 
      print("ADCI Step   : " ..string.format("%g",adcr).." steps")
      print("Current     : " ..string.format("%g",adcI).." mA")
      return adcI

2. READ ADC Process function  and instantaneous Power consumtion calculation 

function readUI()
   gpio.write(ADC_SRC,1)         --select source
   adcV = readADC_Voltage()
   gpio.write(ADC_SRC,0)          --select source
    adcI = readADC_Current()
   pwr = adcI*adcV
   print("Power       : " ..string.format("%g",pwr).." mW")

3. Number format function for proper LCD printing

nr_format = function (fnr,unit)
   if (fnr > 1000) then fnri=fnr/1000
                        uniti=string.sub(unit, 2)   
                        nrf=string.format(" %.3f%s ",fnri, uniti)
   if (fnr < 100) then 
                    if (fnr < 10) then 
                                   nrf = string.format("  %.1f%s ",fnr, unit)
                      else nrf = string.format(" %.1f%s ",fnr,unit)
    else nrf = string.format("%.1f%s ",fnr,unit)
   return nrf

4. LCD Print – > Voltage / Current / Energy / Power

For more details about the I2C LCD Driver , please take a look at the ST7032i LCD Driver Article

LCDout = function()
   if (t==0) then st7032i:lcd_clear() end
   if (adcV > 1) then 
      adci = nr_format(adcI,"mA")
      pwrp = nr_format(pwr,"mW")
      cpct=cpct+pwr*0.002778 --every 10 sec readings
      cpctp = nr_format(cpct,"mWh")
      t = t +1 
  else  tmr.stop(0)
        dtime = t/360 
        st7032i:lcd_print(0,1,string.format("Disc.Time:%.2fh ",dtime))
        st7032i:lcd_print(0,2,"Energy: ")

5. MAIN program

st7032i:lcd_print(1,1,string.format("Battery Monitor"))
st7032i:lcd_print(3,2,string.format("Starting ...")) 
 tmr.alarm(0, 10000, 1, function() readUI() LCDout() tmr.delay(1000) end)


  For testing, just save the code on ESP as ‘blms.lua‘, restart ESP and run:   
            dofile(“blms.lua“)      — Start the Battery Live Monitoring System

                                    Running BLMS program

    If you want the BLMS software to start automatically when your CBDB module starts or reboots, then you neet to create and add some lines in your ‘init.luafile:
            dofile(“blms.lua“)      — Start the Battery Live Monitoring System

Save the code on ESP as ‘init.lua‘, restart ESP. It should reboot and restart automatically the program.

That’s all for today, next time we will continue with Web Interface and online logging system for the BLMS!

Leave a Reply

Your email address will not be published. Required fields are marked *

Related Posts

battery monitor system

Thingspeak – SmartMon Ext Board P4

This is Part 4 of the SmartMon Extension Board series. SmartMon v2.7ex Board  is a extension board fully compatible with Arduino, ESP8266, ARM, PIC & other available MCu’s out there.  As long as your MCU/Dev Read more…

battery monitor system

Smart Mon Ext Board – Software example – P3

This is Part 3 of the SmartMon Extension Board series. SmartMon v2.7ex Board  is a extension board fully compatible with Arduino, ESP8266, ARM, PIC & other available MCu’s out there.  As long as your MCU/Dev Read more…


MCP4728 – 12 Bit I2C DAC Driver – AN1

From today we will move on the Analog interface part of the nEXT EVO Board AN-1 and we will start talking about the Digital to Analog conversion, Analog Autoscaling input and Analog to Digital conversion Read more…