Attached is the concept of my ADC circuit as it stands now.
Runknown is somewhere from 10KΩ to 1MΩ. Rshunt can be anything I want, but is required to keep the input from floating when Runknown nears open circuit (and the ADC reading is all over the place).
Now the ADC says its input impedance is 69KΩ.
That's as far as I've got - is there any "rules of thumb" I should follow?
I guessing, since my ADC is 69KΩ, then Rshunt should be ≈ 69KΩ so current is equally shared across Rshunt and the ADC - the voltage is parallel so that doesn't matter.
What about calculating the value of Ruknown? How would I do that - The ADC gives a value from 0 to 4095 representing the voltage on the input pin relative to Vref: 0 = 0v, 2048 = 50% Vref, 4095 = 100% Vref, etc...
Obviously my reading will never be 100% Vref - the maximum will probably never exceed 50% Vref (Runkown <= 69KΩ).
Guess I just answered my own question there, but I'd still like some input (excuse the pun) on what the experienced players out there would think of...
-KB
Runknown is somewhere from 10KΩ to 1MΩ. Rshunt can be anything I want, but is required to keep the input from floating when Runknown nears open circuit (and the ADC reading is all over the place).
Now the ADC says its input impedance is 69KΩ.
That's as far as I've got - is there any "rules of thumb" I should follow?
I guessing, since my ADC is 69KΩ, then Rshunt should be ≈ 69KΩ so current is equally shared across Rshunt and the ADC - the voltage is parallel so that doesn't matter.
What about calculating the value of Ruknown? How would I do that - The ADC gives a value from 0 to 4095 representing the voltage on the input pin relative to Vref: 0 = 0v, 2048 = 50% Vref, 4095 = 100% Vref, etc...
Obviously my reading will never be 100% Vref - the maximum will probably never exceed 50% Vref (Runkown <= 69KΩ).
Guess I just answered my own question there, but I'd still like some input (excuse the pun) on what the experienced players out there would think of...
-KB
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