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Increase precision in voltage reading #60

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Increase precision in voltage reading #60

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19 changes: 8 additions & 11 deletions Sensor_Examples/BrickPi+_Read_Battery_Voltage.py
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Original file line number Diff line number Diff line change
Expand Up @@ -29,22 +29,19 @@ def get_voltage():
# read data from i2c bus. the 0 command is mandatory for the protocol but not used in this chip.
data = bus.read_word_data(address, 0)

# from this data we need the last 4 bits and the first 6.
last_4 = data & 0b1111 # using a bit mask
first_6 = data >> 10 # left shift 10 because data is 16 bits
# invert first and last bytes to obtain tension
last_byte = data & 0xFF
first_byte = data >> 8
tension = (last_byte << 8) | first_byte

# together they make the voltage conversion ratio
# to make it all easier the last_4 bits are most significant :S
vratio = (last_4 << 6) | first_6

# Now we can calculate the battery voltage like so:
ratio = 0.01818 # this is 0.1/5.5V Still have to find out why...
voltage = vratio * ratio
# convert tension (units seems te be in 0.025/5.5 V or 1/220 V) into Volts
units_per_volt = 220.0
voltage = tension / units_per_volt

return voltage

except:
return False

if __name__ == "__main__":
print get_voltage()
print get_voltage()