Battery Live Monitor System - ESP8266 CBDBv2

 ================== 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.

DO NOT OVER CHARGE / BURN / OPEN Li-Ion Bats

     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:
  http://dirtypcbs.com/view.php?share=5876&accesskey=3d0fd70d53d6dc20c0bf0255f67cde65

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      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 10x200 = 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:  

• CBDB Board ( or any other ESP8266 Board you may like but who has voltage/current measurement capabilities)
  
• INA214  - Current shunt monitor
•  USB adapter (take a look on Part 1 for details about the USB Adapter 
•  Li-Ion Battery Module
• 20 Ω / 5W resistor (or 2 x 10 Ω /5 W in series - even better )
• Connection wires - various colors
  

   Schematics:

  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:

           GREEN  - V+
           BLUE    -  GND
           RED      -  SH_IN+
           WHITE -  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:  
  http://dirtypcbs.com/view.php?share=5876&accesskey=3d0fd70d53d6dc20c0bf0255f67cde65


    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 Inputsda=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
      advr=adc.read(0)
      print("\nADCV Step   : " ..string.format("%g",advr).." steps")
      adcV=advr*dival*resdiv
      print("Voltage     : " ..string.format("%g",adcV).." V")
      return adcV
end

 
2. READ ADC - Current
    
function readADC_Current()
      adcI = 0
      adcr = 0
      adcr=adc.read(0)
      adcI=adcr*divalI
      print("ADCI Step   : " ..string.format("%g",adcr).." steps")
      print("Current     : " ..string.format("%g",adcI).." mA")
      return adcI
end

 
2. READ ADC Process function  and instantaneous Power consumtion calculation 

function readUI()
   gpio.write(ADC_SRC,1)         --select source
   adcV = readADC_Voltage()
   tmr.delay(10000)
   gpio.write(ADC_SRC,0)          --select source
   adcI = readADC_Current()
   pwr = adcI*adcV
   print("Power       : " ..string.format("%g",pwr).." mW")
end
 

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)
   else
   if (fnr < 100) then
                    if (fnr < 10) then
                                   nrf = string.format("  %.1f%s ",fnr, unit)
                      else nrf = string.format(" %.1f%s ",fnr,unit)
                    end
    else nrf = string.format("%.1f%s ",fnr,unit)
   end
  end   
   return nrf
end



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
      st7032i:lcd_print(1,1,string.format("%.3fV",adcV))
      adci = nr_format(adcI,"mA")
      st7032i:lcd_print(8,1,adci) 
      pwrp = nr_format(pwr,"mW")
      st7032i:lcd_print(0,2,pwrp)
      cpct=cpct+pwr*0.002778 --every 10 sec readings
      cpctp = nr_format(cpct,"mWh")
      t = t +1
      st7032i:lcd_print(8,2,cpctp)
  else  tmr.stop(0)
        dtime = t/360
        st7032i:lcd_print(0,1,string.format("Disc.Time:%.2fh ",dtime))
        st7032i:lcd_print(0,2,"Energy: ")
  end
end  

 
5. MAIN program

require('st7032i')
st7032i:init_i2c(sda,scl)
st7032i:init_LCD()
st7032i:lcd_clear()
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.lua' file:
  
            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!