aref external is not external but teenys 3.3V ?

I was doing some testing yesterday and hooked up an external voltage source to the VREF. The voltage was set to 2.81V

Compiled a scetch with analogvref set to external.

Hooked up the 2.81V to vref, I notcied the voltage jumped up to 3.2V....

Looked at the schematics on the teens3/3.1 and see vref is connected to VDDA via a 470ohm resistor and then conected throw a ferrit to 3.3 out...

To me this indicates you can not use an external vref? Or Im i just to tired atm?

gripner said:

To me this indicates you can not use an external vref? Or Im i just to tired atm?

Click to expand...

Two options:
1) Use a shunt-style external reference (zener diode, buried zener, etc.). If you go this route, Paul has already provided you with the current-limiting resistor you will need. Simply run the zener from AGND to AREF and you're done
2) Remove the 470 Ohm resistor (it's relatively easy) and attach any reference you want to AREF