Analog Input external voltage ->Basic Electronics Arduino Problem oO??

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1

Hey everybody.

my DIY Dyno is ready soon. The RPM measurement with the hall sensor works fine :slight_smile:
I want to measure the torque with a strain gauge. This works pretty well as stand alone system.

The problem:

1 . The arduino is powered by USB. The DMS amplifier is connectet to a power unit at 8 volts. The output pins go to GRD and Analog input 0 at the arduino...
--> i measure a voltage of about 3.7 Volts. When i load the strain gauge the voltage affects betwen 2.0 and 3,7 V...
System works all is fine :slight_smile:

  1. The arduino and the DMS amplifier are both connectet to the power unit at 8 volts. The arduino is connected by the DC power Jack. So when i don't connect the Pins to the Analog input i measure a Voltage of 3.7 V with the multimeter. When i connect the pins to the analog input i measure 6.44 V and the DMS does not work. ??

Ok, i tink its a simple understanding problem of basic electronics :wink: I'm mechanical engineer but i want to learn :wink:
So has anyone an idea?

Best regards Phil

2

You can not feed more than 5V into the analogue input without damaging your Arduino.
You must ensure that you do not do this.

The output pins go to GRD and Analog input 0 at the arduino...

To me that says you have a differential output on that sensor. This means you could put +8V and -8V into the analogue input, negative voltages are double bad.
However if you are powering the arduino from a single ended 8V that you are powering the amplifier from this will not happen.

We need to know about your amplifier, link to the data sheet please, and also exactly how it is wired it up, schematic please.

3

Hey
thanks for the reply

The amplifier gets the 8V to work! The output from the amplifier is not 8V to the arduino analog input. its the 3.7 V!! Th analog input gets no negative values. Ive testet with the multimeter.
Here are the links. That idea with the differential source seems good. I have to read some information :wink: i sketch a shematic and attach it!

http://docs-europe.electrocomponents.com/webdocs/001b/0900766b8001bb5c.pdf
http://docs-europe.electrocomponents.com/webdocs/001b/0900766b8001b962.pdf
http://docs-europe.electrocomponents.com/webdocs/112a/0900766b8112a279.pdf

Regards Phil

4

Ok it seems to be a differential voltage sensor.

The two output wires:

Measures one to ground: -4.2V

Measured the other to ground: 8.3V

--> -4.2 + 8.3 = 3.7 :astonished: :astonished:

Idea: Put each wire into a analog input and subtract them. ]:smiley: negative voltage :frowning:

Regards

5

The amplifier gets the 8V to work!

But the data sheen says it needs a split supply. If you only have a single ended supply then you will need to make a virtual ground by using a pair of resistors.
This will put ground at +4V and any signal can be 4V above or below this point.

What we need to see is a schematic of how you are wiring it up.

6

Hey,

thanks! Problem solved. I generated a virtual ground. This was the isue

works fine!

Best regards