Go Down

### Topic: Strange Analog Input Problem (Read 3775 times)previous topic - next topic

#### oldnoob

##### Feb 11, 2013, 11:52 pm
Hello,

We are trying to connect 5v linear output from sensor to arduino analog input.

Everything works except. Sensor output was stuck at 2.24v. When we disconnect ground from arduino and check the sensor output with multimeter everything works well.

Sensor has one 12v volt input, one ground for sensor circuit one ground for sensor itself. We wire sensor with external adapter + to 12v input, both ground and arduino ground connected to external adapter.

If we do not connect arduino ground sensor reading from arduino was unstable. However sensor linear output works as expected.

Sensor circuit was propetary and we do not know anything about it. Producer looks helpful and does not interesting with arduino usage.

So ? is there any work around  and or explanation for this problem.

Our best regards.

#### Krodal

#1
##### Feb 12, 2013, 12:48 amLast Edit: Feb 12, 2013, 01:03 am by Krodal Reason: 1
Use a resistor of 1k between sensor and Arduino input, to protect the Arduino. Perhaps the sensor generates a spike of 12V during startup.
Use an other input pin of the Arduino, you might already have damaged an input pin.

Did you set the internal reference of the Arduino ? (you should not).
Did you connect the sensor to Aref ? (that is not an input).
Did you connect Aref to something else ?
If the sensor is stuck at 2.24V, is that measured with the Arduino or with a multimeter ?

If you still have problems, we like to have more information.
Which Arduino Board ?
What sensor, please paste a link to it.
Can you draw how everything is connected.

If grounding is a problem, you could power the Arduino with a battery, or via the usb with a laptop with its power supply disconnected.
The impedance of an Arduino input is very high. It might even be higher than the impedance of the multimeter. So it doesn't make sense that the voltage drops.

#### oldnoob

#2
##### Feb 12, 2013, 09:16 pm
Hi Krodal,

Many thanks for replying.

We setup same kind but different made sensor befor and run without any problems. Sensors are highly sophisticated, these 0-5v linear outputs are mostly used on independent displays. We do not expect any spikes or similar errors (of course there is always be possible and if this happen it should have to our sensor circuit spesific).

No we do not use AREF in any kind.
I set the

analogReference(INTERNAL);

and remove it after your advice nothing changed

We measure voltage both arduino and multimeter.

Arduino is Olimex 328
https://www.olimex.com/Products/Duino/AVR/OLIMEXINO-328/

https://www.olimex.com/Products/Duino/AVR/OLIMEXINO-328/resources/OLIMEXINO-328-schematic.pdf

Sensor is custom made wideband reader. It has 2 ground one for sensor one for sensor heater.

We power arduino from usb and power sensor from 12v adaptor. Both sensor grounds plus arduino grounds was connected to adapter ground. Anykind of ther ground setup generate veird readings from analog input. Arduino input was a5, (also I change it for testing nothing changed)

The other device has one ground and when we connect the arduino ground it works withouth any problem.

Also I maybe can't explain problem clearly.

Sensor generates 0 to 5 volt linear output. when we connect to arduino it works 5 volt to 2.24 volt and does not go bellow. under normal circumstances it should go to 0v or 0.1v.

However it swings 5v to 2.24v

Best regards...

#### retrolefty

#3
##### Feb 12, 2013, 09:28 pm
Quote
Both sensor grounds plus arduino grounds was connected to adapter ground.

Is 'adapter ground' in you case some kind of attachment to the AC power ground? If so that should not be required and could be a source of your problem. Your sensors DC power common and arduino DC power common need to be wired together, but no need to be wired to true 'earth ground'.

Lefty

#### oldnoob

#4
##### Feb 12, 2013, 11:01 pm
Yes,

I mean both sensor grounds and arduino ground connected to AC Power ground.

Well if we connect grounds to arduino ground. We did not get any stable meaning results. In old  device this setup was working.

Interesting thing was with this setup. It works to half way.

#### Krodal

#5
##### Feb 12, 2013, 11:31 pm
retrolefty, it is amazing how you solved it.

oldnoob, a good grounding is important. With sensors it is very important.
Perhaps you can make a drawing of it. Or you can stretch your circuit as one long circuit and check how the ground is.
The ground of the sensors should go the the ground of the Arduino, because the signal is going to the Arduino and that should be accompanied by the ground.

#### oldnoob

#6
##### Feb 13, 2013, 08:03 pm
Ok,

I got it, sensor circuit must use arduino ground.

Both circuits are commercial and closed source. Second one (which does not work) was very small and half price .

Thats why I desperately looking for help.

Anyway...

Thanks lot for your time.

My humble regards

#### michinyon

#7
##### Feb 14, 2013, 01:26 am
What sort of sensor is it ?
Are you sure it is supposed to be generating a voltage output ?

#### MarkT

#8
##### Feb 14, 2013, 03:58 pm

Hello,

We are trying to connect 5v linear output from sensor to arduino analog input.

Everything works except. Sensor output was stuck at 2.24v. When we disconnect ground from arduino and check the sensor output with multimeter everything works well.

Well put a 10k resistor to ground from the sensor output then - multimeters have a definite load resistance, analog pins are
effectively infinite resistance.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

#### oldnoob

#9
##### Feb 18, 2013, 09:23 pm
Hello again,

Using 10k resistor does not change much. Just output range changed. After resistor sensor start to give 3. ish v and down to 1.9 ish v.

Anyway today one of our friend which has some car electronics repair experience suggest, maybe ampere of the sensor output was too low. So aduino analog voltage noise (which we detect every analog port of arduino) generates resistance against sensor output.

is this make any sense ?

Regards

Go Up