Hi Folks,
Slightly related to my other thread about the pull-down resistor for an opamp (All suggestions will be in v2)
I have a problem, which to me, is weird. See diagram attached. I realised I made a slight mistake of the diagram though, Ill explain later.
When the shunt is connected (low side , common ground) and the ADC (Netduino) and OP powered by a separate power source (LiPo battery or USB) then all is well The netduino is happy and current readings are as expected.
When I then hookup the same battery which supplies the load (12V Pb battery) to the voltage divider (up top on the diagram, sorry, no labels :|) and connect that to the netduino, I lose the current readings.
I am guessing I have some sort of common ground / feedback etc etc which is causing a problem. Having looked at the diagram I cannot see why so fresh out of ideas.
In short, I cannot measure voltage (12V) and low-side shunt voltage at the same time. The shunt values vanish.
Is there something else I should be doing? Ive read about DC-DC isolation convertors (have one winging its way to me)
Thanks
Crispin
Slightly related to my other thread about the pull-down resistor for an opamp (All suggestions will be in v2)
I have a problem, which to me, is weird. See diagram attached. I realised I made a slight mistake of the diagram though, Ill explain later.
When the shunt is connected (low side , common ground) and the ADC (Netduino) and OP powered by a separate power source (LiPo battery or USB) then all is well The netduino is happy and current readings are as expected.
When I then hookup the same battery which supplies the load (12V Pb battery) to the voltage divider (up top on the diagram, sorry, no labels :|) and connect that to the netduino, I lose the current readings.
I am guessing I have some sort of common ground / feedback etc etc which is causing a problem. Having looked at the diagram I cannot see why so fresh out of ideas.
In short, I cannot measure voltage (12V) and low-side shunt voltage at the same time. The shunt values vanish.
Is there something else I should be doing? Ive read about DC-DC isolation convertors (have one winging its way to me)
Thanks
Crispin
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