1 gram scale

Hi, Guys,

I’m using a 1 gram strain Gage (it came out of a Chinese product). It is used for measuring US money, which weights 1 gram per banknote. I am running the signals to a solder board and then to a breadboard using 22 Gage wires to a INA125P. The problem i’m getting is that the scale seems to fluctuate too much even when I try smooth the signal in software by taking the last 4 readings.

I want to replicate the same thing. As USD currency weighting scale.

My signals look something like this:

141, 142, 141, 142, 141, 142, 141, 142.

My question is, is this normal? Can anyone recommend if this is normal or is the anyway to improve it.

Cheers,

Cameron.

cameronasmith: My question is, is this normal?

Who knows? Try reading the datasheet...

cameronasmith: anyway to improve it.

Try putting a big ceramic capacitor across the output.

cameronasmith: 141, 142, 141, 142, 141, 142, 141, 142.

Are these weights indicating either US$141 or US$142?

anyway to improve it.

Not use a hacked up cheap Chinese strain gauge?

the reading: 141, 142, 141, 142, 141, 142, 141, 142 is when it has 1 USD on the weight.

I cannot read the datasheet because it came out of another system, and it does not contain any serial number.

Try putting a big ceramic capacitor across the output.

What size would you recommend, fungus?

Thanks

cameronasmith:

Try putting a big ceramic capacitor across the output.

What size would you recommend, fungus?

What have you got?

Try that one then...

I tried a .1uf and it didn't really make any difference.

cameronasmith: My signals look something like this:

141, 142, 141, 142, 141, 142, 141, 142.

Where, exactly, are these numbers from? Are they values from the ADC?

an error in the least lsb is not unexpected. since two banknotes should equal 282 or thereabouts, you are way above any error induced by a fluctuation in the lsb.

I think that is enough error to be off US$1 in a US$100, which isn't going to work.

Hey, Guys,

I'm sorry, I don't think I specified that the scale went like this:

421 = 1 bill

424 = 2 bills

427 = 3 bills

the problem is that the numbers are not that consistent.

Cheers

cameronasmith: the problem is that the numbers are not that consistent.

So are you saying that 4 bills might be 429, 430, or 431?

What's the reading for 100 bills? 718?

Is 141 one the base reading with nothing on the scale?

So little information. So many questions.

I think the INA125P blows only the signal up but you have in the best case still the 10bit resolution of the Arduino. If you boost with the wrong gain you can not use the full range and you have less than 10bit

It should help to use an external ADC (with integrated op amp). I have used the ADS1231, a 24bit ADC and also the HX711 successful with a load cell. For the HX711 have a look at this break out board http://www.dfrobot.com/index.php?route=product/product&filter_name=load%20cell&product_id=1031#.Uz8NRh75FTs

It is also a good idea to smooth the readings by a running media, see http://playground.arduino.cc/Main/RunningMedian but this will not help if the raw value altered +/-1 around.