As soon as I unplug my Arduino from USB and only use the VIN pin with my 9 V power supply, the analog readings from my Arduino start to get unstable, which means the value fluctuates much more than with USB connected. When I reconnect USB again, the readings are stable again.
I'm trying to build a load scale using a load cell, an INA125P and the Arduino, using this setup here: Instrument Amplifier Calibration.
Therefore I need stable readings. For example, I wrote some code to convert the
analogRead() value to grams. While USB and VIN (9 V) connected, I get a stable reading of about 8.3 to 8.7 grams when I put a weight of 8.5 grams on the scale. As soon as I unplug USB, the LCD shows values from 7.8 grams up to 9 grams.
Unfortunately, I don't have any other power supply which I could use to test. I've already tried to use a 9 V battery with the same results. Do I maybe need some additional de-coupling capacitors?