currentMeter.py

#!/usr/bin/python3
import time



# Import the ADS1x15 module.
import Adafruit_ADS1x15



'''
   Script to read current from  ACS712 30A  using ADS1115 converter


   ACS Vout      2.5V with  66mv/per Amp

                 The range  will be 0 to 2A so  the ACS712-30A is ~66mv/A
                 0A is then  VCC/2
                 2A is  VCC/2 + 66mv*2
                 if VCC is 5V then  0A=2.5V  and 2A =  2.632V

                 The Voltage on the ADS1115 is 3.3V from the Raspberry Pi we will need to take Vref = 2.048V.
                 Then  we will need to reduce the Vout from the ASC712-39 below the 2V using a resistor divider

                 V IN0 =  ACS712-30A Vout * R1 / (R1+R2)

    ACS VCC      Because ACS712-30 output is related to the VCC.
                 Ee will need to read the VCC at the ACS712-30 and compensate the return voltage from it.
                 I can't figure out if the 66mv/A is also proportional to VCC but I will assume it.

                 Then we should be able to compensate  the VCC shift using  5V has  reference. This eliminate
                 the recalibration of the offset if  the voltage at the ACS712 change.

    ADS1115      IN 0  ACS712-30A  using a register divider  R1/R2
                 IN 1  VCC of the ACS712-30 using a register divider  R3/R4



    register divider

                 R1    ACS712-30 output to  ADS1115 IN0
                 R2    ADS1115 IN0 to GND

                 R3    VCC at ACS712-30   to ADS1115 IN1
                 R4    ADS115 IN1 to GND

'''


#constant definition

ACS712_mV_to_Amp = 66e-3
ACS712_VOffset   = 2.5

R1 =  4500.0
R2 =  10000.0

R3 =  10000.0
R4 =  4500.0

#use 2.048 Vref
GAIN = 2


#Conversion of ADS1115 to Volt

def ConversionToVolt(values):
   return(values * 2.048/32767.0)

#Calculate the ACS712-30 output
#From ADS1115 IN0 , calculate Vout before the resistor divider R1/R2
def getRealACS712Vout(Vin):
    return(Vin * ( R1+R2)/(1.0 * R2))


#Calculate the ACS712-30 VCC
#From ADS1115 IN1 , calculate Vout before the resistor divider R3/R4

def getRealACS712Vcc(Vcc):
    return(Vcc * ( R3+R4)/(1.0 * R4))

try:

  while True:


    #average 5 readings,IN0 and IN1 in alternance, to remove noise from DC/DC power supply

    IN0Avg=0
    IN1Avg=0

    for  i in range(5):
      IN0Avg= IN0Avg + read_adc(0, gain=GAIN, data_rate=128)
      IN1Avg= IN1Avg + read_adc(1, gain=GAIN, data_rate=128)


    IN0Avg = IN0Avg /5.0
    IN1Avg = IN1Avg /5.0

    print("IN0:{}  IN1:{}".format(ConversionToVolt(IN0Avg),
                                  ConversionToVolt(IN1Avg)))


    #calculate  every thing now

    #get ACS-712 Vout and VCC

    ACS712Vout = getRealACS712Vout(ConversionToVolt(IN0Avg))
    ACS712Vcc = getRealACS712Vcc(ConversionToVolt(IN1Avg))

    print("Vout:{}  VCC:{}".format(ACS712Vout,ACS712Vcc))

    #Normalize ACS712 Vout  for VCC=5.0

    VNormalize = ACS712Vout *  5.0 / ACS712Vcc


    #ok calculate the current

    IOut =  (VNormalize - ACS712_VOffset) / ACS712_mV_to_Amp

    table=[]
    #record IN0 A2D
    table.append(IN0Avg)
    #record IN1 A2D
    table.append(IN1Avg)
    #record IN0 Voltage
    table.append(ACS712Vout)
    #record IN1 VCC
    table.append(ACS712Vcc)
    #record ACS712 current
    table.append(IOut)

    print("0:{0:5} {2:1.3f}V {4:2.2f}A\t1:{1:5} {3:1.3f}V".format(*table))

    time.sleep(0.5)

except KeyboardInterrupt:
   pass

Hello @danjperron
I have a question.
Where did you get these specific values for R1, R2, R3 and R4?
And why should R3 and R4 be in those specific places as you wrote?
"R3 VCC at ACS712-30 to ADS1115 IN1
R4 ADS1115 IN1 to GND"

I use Vref on the ADS115 to be 2.048V so voltage output can't be higher than 2.048V.

VCC on ACS712-30 is 5V so 0A is 2.5V.

So the resistor divider is to be sure that the ACs712 output is below 2.048V with the current on it.

if you have 2A on the ACS712-30 you will get (in theory) 2.5V + 2A*66e-3V/A => 2.632V.
Since the ACS can't read more than 2.048V than the resistor divider will put the voltage below 2.048V.

2.632V * (10000/(10000+45000)) => 1.81V

Depending of your current you will need to check what is you maximum current and set according to it.

But I got a better method now. I'm using a potentiometer to get the zero since the A/D could do differential. Adjusting
adc1 via the potentiometer to get 2.5V to be the same voltage than adc0 at no current. Using this method the ACS712 doesn't need resistor divider. Then the maximum ADC is 3.3V.

https://www.dropbox.com/s/7sxdzjxtyqslmg4/solar1_bb.jpg?dl=1

N.B. the current ADC library doesn't support differential but it is easy to add. Just check the data sheet and add it on the python library.

@danjperron I sent an email to You with one more issue. Thank you in advance for your help!