Strange analog readings.

[cameronasmith]

Hi Guys,

I have an INA125 plugged into a breadboard (i read that this might be a problem) with a strain gauge connected to an Arduino analog pin.

When I take readings it seems to jump around. For example:

101, 102, 101, 101, 102, 101, 101, 101.

Is this normal for a strain gauge? And can anyone recommend a way to not make the signals so erratic.


Thanks,

Cameron.

[PA0PBZ]

I don´t see a problem here: imagine that the signal is 101.5, what readout would you suspect?

[cameronasmith]

Hi, paopbz,

I'm sorry, I don't think I explained it very well. If I put a 100gram weight on the scale. The reading will jump around like:

202, 201, 201, 202, 202, 201.

If I put a 101 gram weight on the scale I will get something like this:

203, 202, 203, 203, 203, 202.

You can see how this can become a problem when weighing in 1 gram increments.

I really need it to just give me one reading.

Thanks,

Cameron.

[KJDS]

You will always have some variation due to noise.

Just display an average.

[lewis]

You need some digital averaging! I use an IIR filter like this: http://electronics.stackexchange.com/questions/30370/fast-and-memory-efficient-moving-average-calculation

Think about why the reading will jump around and why you will never get a single consistent value.

[PA0PBZ]

Hi, paopbz,

I'm sorry, I don't think I explained it very well.

I think you did explain it very well, just look at my answer again and think about it...

[kfitch42]

Expanding on the concept a bit more, this is a case were noise can be a good thing. By using an average you can get a more precise reading than what you get with a single reading.

Think about those cheap digital oral thermometers, they can take quite a while to give a reading ... but the ones they use at the doctor's office only take a couple seconds.

This is because the cheap ones are using a cheaper/noisier sensor and wait until the average settles down. The more expensive ones at the doctor's office use a better(more expensive) sensor so they don't have to average for so long.