Pololu G2 current sense output for Spindle load meter?

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15 Dec 2018 19:06 #122452 by 3D-Master
Hello,

i am currently using a Pololu G2 PWM driver to control my Servos and it has a current sense output (approx. 20 millivolts per amp) could i use my 7i73 analog input for this? what resolution do the 7i73 analog inputs have? If not what would be suitable/easy to implement and fast enough? I already use 2 of the 4 analog inputs for spindle and feed override using Potentiometers but the voltage coming out of the Pololu driver will never be 3,3v (that would be 165 amps, maximum is 21 amps continuous/current chopping @50amps). I want to implement a Spindle Load meter and maybe also axis load meters as well. (if there is a board out there compatible with Mesa hardware which has a minimum of 7 analog inputs please let me know)

thanks
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15 Dec 2018 22:02 #122456 by PCW
It sounds like a direct signal from the current sense resistor
(too small signal), plus theres probably quite a bit of common mode
noise (since the PWM power ground = current sense common)
and enough ground bumping that you might damage the 7I73
analog inputs if directly connected.

One solution is to add a differential amplifier (OpAmp+ 4 resistors) with a gain of 10 or so you can reject the common mode noise, and amplify the full scale signal, and protect the 7I73 analog inputs from voltages < -.6 and > +5V
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17 Dec 2018 00:51 #122498 by andypugh
I am currently playing about with one of these, though I am having some trouble with the SPI comms.
www.ebay.co.uk/itm/ADS1256-8-Channel-24B...ion-ATF/192428635947
I suspect that it might not be very easy to interface with a Mesa BSPI, due to the setup required so probably an Arduino and a UART would be required.
(I keep meaning to look in to the possibility of an Arduino acting as a Mesa Smart Serial slave)
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