Raspberry Pi only reading 8 bit bus voltage.

[pliedl]

I wasn't getting linear discharge graphs on a 12v battery discharge. I am a novice but I found the solution to the problem on the Adafruit forum. I don't how to go about modifying the software but here is the fix that worked for me:

To overcome the issue of 8 bit voltage and read bus voltage down to millivolts resolution apply the following changes to the file "Subfact_ina219.py"

FIND LINES

def getBusVoltage_raw(self):
result = self.i2c.readU16(self.__INA219_REG_BUSVOLTAGE)

"# Shift to the right 3 to drop CNVR and OVF and multiply by LSB
return (result >> 3) * 4"

REPLACE WITH

def getBusVoltage_raw(self):
result = self.i2c.readList(self.__INA219_REG_BUSVOLTAGE,2)
if (result[0] >> 7 == 1):
testint = (result[0]*256 + result[1])
othernew = self.twosToInt(testint, 16)
return othernew
else:
return (result[0] << 8) | (result[1])

FIND LNES

def getBusVoltage_V(self):
value = self.getBusVoltage_raw()
return value * 0.001

CHANGE MAGNITUDE MULTIPLIER TO 0.0005 AS BELOW

def getBusVoltage_V(self):
value = self.getBusVoltage_raw()
return value * 0.0005

---

[charkster]

I did not see the above change in the latest Subfact_ina219.py
I use a different I2C class that has a default endian (not the included Adafruit_I2C.py).
The above change has the endian specified in the readList manipulation of bytes.
It is a superior solution as readList is always the same, while readU16 can be different.
I manually added the above change, as I needed it.