Current reading like OS3

[951calguy]

How hard is it to get a current reading on OSPi like you guys have on OS3?
is there a step by step?

[Ray]

Not too hard — there is 0.2ohm current sensing resistor combined with an op-amp based precision rectifier. The signal can then be fed into the ADC (on OpenSprinkler, the microcontroller itself has ADC pins, whereas RPi doesn’t have built-in ADC but OSPi has a PCF8591 ADC chip on board).

[951calguy]

thanks Ray. I have been able to build my own OSPi but I am not that technical yet, so any way to tell me exactly where these parts would go on the board? Also part numbers and where to get them from? Thank you again Ray.

[951calguy]

Can anyone else help with this?

[Ray]

If you download the OS3.0 main controller EagleCAD files:
https://github.com/OpenSprinkler/OpenSprinkler-Hardware/tree/master/OS/3.0/Master
and open the .sch in EagleCAD, you will see a section that looks like below. That’s the precision rectifier circuit. What it does is to rectify the AC voltage that falls on the 0.2ohm current sensing resistor to DC voltage, then feed that to an ADC pin.

Attachments:

1. 

   os30_precision_rectifier.png
   

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