Hello,
I'm trying to read resistence changes on strain gauge. I'm using AD8221 In-Amp and need to shift output lever with REF pin. REF pin should be driven by low impedance source. Then i should use OP-AMP to drive that.
I'm using ESP32 wroom module to drive that thing and now i'm thinking about using internal DAC from ESP to drive REF pin. But is that low or high Z?
Not sure why you are using an AD8221 opamp for this. Post your circuit diagram.
Restrictions on supply voltage and output swing and the ESP A/D could mean you're not getting a lot of A/D values returned. A HX711 breakout board (the one with separate digital supply) could be a much better solution for your strain gauge.
Leo..
Im using AD8221 IN-AMP 
with pre-set gain.
Actualy AD8221 works way better for me than HX711, becase of better sample-rate (only up to 80Hz in HX711).
I attach my circuit diagram. I use 350R strain gauge, resistors 15-17 are 348R, BA728F is LM358 (I've been searching in lib just for similar look to lm358). Everything works great, but I'd like to throw LM358 driving REF pin out of that project to make it simpler.
Then, can I drive REF pin directly off ESP32 DAC without messing CMRR?
The AD8221 has a minimum supply voltage of ±2.3volt (4.6volt).
My bad on schematic. that would be 5V. But that's not what i asked for..
Details matter.
Note that the AD8221 on a 5volt supply can output a higher voltage than a 3.3volt pin should see.
Don't know anything about the DAC of an ESP-32, but mid-voltage generated by a DAC should be ok.
Leo..
