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A0 to A5 crosstalk - amplified load cells - 5V PRO Trinket
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A0 to A5 crosstalk - amplified load cells - 5V PRO Trinket

by Flinkly on Thu Apr 25, 2019 10:39 pm

Hi

I've made a test fixture to measure clamp force of heatsink to "hot" parts (6 load cells at once, not measured when hot, T=0 testing) while applying a measured torque to screw/enclosure. Trying to create a torque spec to get desired clamp load + variation. I will be adding a torque sensor as well, but wanted to sort out this voltage cross talk.

anyways, i am getting cross talk between load cell analog inputs (A0 to A5, 6 total). if i just have 3 load cells installed (provide .5 to 4V output) and apply pressure, the remaining 3 analog inputs also go up by a significant amount. Am i missing something to reduce any noise? a cap or resistor somewhere? i'm an ME, so this sort of thing is lost on me.

I'm using a Pro Trinket 5V and using the USB 5V power to supply the load cells, and reading back their voltage to convert to clamp load. Load cells are TE FC2231 load cells.

Let me know what information would be helpful to troubleshoot, if it's not something super obvious.

thanks!

https://www.te.com/commerce/DocumentDelivery/DDEController?Action=showdoc&DocId=Data+Sheet%7FFC22%7FA5%7Fpdf%7FEnglish%7FENG_DS_FC22_A5.pdf%7FFC2231-0000-0100-L

Flinkly
 
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Re: A0 to A5 crosstalk - amplified load cells - 5V PRO Trink

by adafruit_support_bill on Fri Apr 26, 2019 5:58 am

Like most microcontrollers, the Atmega-328 in the Pro Trinket has only one ADC. The 6 analog pins are connected to the same ADC via a multiplexer. When switching between pins, it can take some time for the signal to settle to the new value. This is more of an issue with high-impedance signal sources.

One simple approach is to take two readings for each channel and discard the first. The first reading will cause the multiplexer to switch channels to the desired pin. The second reading should give you a more stable value.

adafruit_support_bill
 
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Re: A0 to A5 crosstalk - amplified load cells - 5V PRO Trink

by Flinkly on Fri Apr 26, 2019 2:10 pm

That makes total sense, both with the microcontroller capability and what i'm seeing.

Thank you!

Will report back when i've changed the code and have positive results.

Flinkly
 
Posts: 9
Joined: Thu Oct 08, 2015 3:31 pm

Please be positive and constructive with your questions and comments.