3 replies to this topic

[Igor Kondrasovas]

Hello,

 

We are working in a project where we have to read data from electronic weight scales. The signals will come in 4-20mA signals that must be processed by Netduino Plus.

 

Suppose we solve the current to voltage conversion and deliver 0 to 3,3V to the Netduino analog input. We know there is some noise and some filtering may have to be applied. I believe this is common to most class of microcontrollers.

 

In order to minimize this noise, we were thinking about using some external ADC with SPI or I2C interface, like the Adafruit ADS1015 or MCP3008.

 

I would like to know if using these (or any other) chips or breakout boards will potentially provide lower noise levels? I mean, do they have a better noise immunity/treatment compared to the native Netduino ADC filter?

 

 

Thank you,

 

Igor.

[NooM]

iam using the mcp3201. its ok, but well.

 

my netduino has nearly no noise at adc.

iam powering it either from batteries or a stabilized wall supply, and i have some

capacitors on the power rails.

 

when i tried a cheap supply i got a lot of noise, maybe you should look there first

 

 

the benefit of an external adc is ofc you can supply 5v

and mini users like me can add an analog reference

[HiredMind]

Do have particularly high speed requirement for each measurement? I would think that sampling many times over 1 or 2 seconds and then averaging the results would cut any noise down to zero.

 

A bulletproof way to do it would to calculate the amount of change over time (I think statisticians call it standard deviation?  I'm not sure), and when that drops down below a certain threshold, lock in the measurement.  That way if your ADC should start having noise problems you still get the right measurement, it just takes longer. 

[StefanUSMC]

I am an Industrial Weighing Device Service Technician. The biggest issue with the ADC on the ND+ is that it is only 12-bit. A legal for trade scale (At least here in the US) has up to 10,000 divisions. This means that at 12-bit (4096 counts) you will not be able to match the resolution of the scale. In this case, I would use a higher resolution ADC personally. Not really an answer to your question, just some input on issues I have seen in the field.