Why is my INA219 current sensor gives a negative currentmA and Shunt voltage? My sensor is connected in a glucose test strip connector. The current is from a glucose biosensor? Is it possible that my INA219 is damaged?

  • Did you connect it the wrong way around? Does the glucose strip maybe produce a voltage?
    – Gerben
    Feb 19 '19 at 12:01
  • I connect it according to the schematic. The glucose test strip produce current Feb 19 '19 at 12:14
  • 1
    Could you show us the schematic? You haven't given us a lot of information to go on.
    – Gerben
    Feb 19 '19 at 12:16
  • make sure the ground path is low-impedance between the MCU, the INA, and the sensor.
    – dandavis
    Feb 19 '19 at 17:23

The "sign" of the INA219 shows the direction of flow of the current. Current isn't either "positive" or "negative", it has a direction. The sign is just used to represent that direction.

It's like a car. It has a speed. That speed could be in the forward direction, or the reverse direction. It could be going 5 miles per hour forwards, or 5 miles per hour backwards. Either way, it's 5 miles per hour. However the backwards direction could be represented as "minus 5 miles per hour". It doesn't mean that you're doing a negative speed (there is no such thing), but that your speed is in a "negative direction".

This "speed" and "direction" are combined together to create "velocity", which is "speed relative to some arbitrarily chosen 'normal' direction and speed".

At this point the "velocity" can be represented as a 2D vector, with forward velocity in the + direction, and reverse velocity in the - direction.

But that's all a bit of a digression. All it means is that the "-" is meaningless if you don't care about the direction of current flow. If all you care about is the quantity of current you can discard the "-" completely. The simplest way is:

current = abs(current);
  • Last month I measure the led with a 9 volts battery and the output is the same as I expected but when I tried it this week it gives negative values Feb 19 '19 at 12:13
  • Were the values (about) the same, but negative?
    – Gerben
    Feb 19 '19 at 12:18
  • No. It changed values and become negative Feb 19 '19 at 14:01
  • Did you calibrate it correctly?
    – StarCat
    Mar 15 '20 at 16:13

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