Dual Power Supply on Arduino

Hello,
I have a load cell and an amplifier (RS 435-692 stain gause) the power supply of amplifier is +-15V(negative and positive voltage). Also a voltage divider because the output is 11V and I want to connect it on analog pin of arduino.

My problem is when i connect the adruino GND with the other grounds (of power supply ). Then my Vin change to negative number and the voltage divider doesn't work right.
I think the problem is on dual power supply because I have on ground +15V for the -15V of amplifier.
What I can do ?

If the power supply for the strain gauge is isolated then you can connect the Arduino GND to the -15V of that supply. The guage will then output 0-30V.

Otherwise it gets complicated.

fungus:
If the power supply for the strain gauge is isolated then you can connect the Arduino GND to the -15V of that supply. The guage will then output 0-30V.

Otherwise it gets complicated.

I would use voltmeter to check that before connecting. You can do a huge short circuit.

fungus:
If the power supply for the strain gauge is isolated then you can connect the Arduino GND to the -15V of that supply. The guage will then output 0-30V.

Otherwise it gets complicated.

How can you say that without a schematic???

The NORMAL connection of a Wheatstone_bridge Wheatstone bridge - Wikipedia
No force on the cell gives zero volt relative GND.
With positive force on the loadcell it gives positive voltage out
With negativ force on the loadcell it gives negative voltage out
GND on the amplifier must be connected to the arduino GND.
Alex Tr have some problem with the powersupply if he power the Arduino from +15 volt it should work IF the powersupply can give enought with current. And a voltage regulator with big cooler.

I can not say this is right without a schematic of all connection between the bridge, amplifier, Arduino and powersupply.

Fungus you guess to much. Connecting your way have to be complicated, I think

Pelle

Fungus has it right. when you connect any dual supply sub-system to the arduino, you ALWAYS connect the sub-system's negative output to the arduino's ground and use voltage dividers to drop the signal voltage levels to what the arduino can tollerate. otherwise, you make'em big smoke.........

Can you publish a schematic with a weastone bridge, a differential amplifier and the ADC connected to the negative supply.

What voltage do you get when the the loadcell are unactivated?

Why a voltage divider when you can set the amplification by using the right resistors in the differential amplifier?

Have you ever build things with bridges and OP:s?

Pelle