The updated 'Rev B' board is identical to the original 'Rev A' board except that we have added an "internal analog reference (AREF)" to the Netduino. [We also removed the unused I2C resistors.] [see schematic]
The new internal AREF is selected BY DEFAULT on the new boards. The new internal AREF is an optional-use feature and the existing external AREF (via AREF pin header) may be used instead.
Why the added circuitry? Lots of Netduino users have never used analog inputs before. Many power users like to wire their external AREF manually for maximum accuracy--but having a default internal analog reference makes it even easier to get up and running with Netduino.
The new internal 3.3V analog reference (fed by the 3.3V onboard power regulator) provides the following benefits:
1. Enhanced Arduino shield compatibility--no need to modify shields to wire 3.3V to AREF.
2. Arduino shields which provide a 5V external AREF won't feed a potentially damaging voltage into the MCU (by default the internal AREF is used -- the external AREF is now selected in code).
3. Even easier to get up and running with Netduino
4. Simplified wiring for users powering their analog sensors from the 3.3V power header.
We will be adding a new command to the Netduino SDK to select the external AREF on the new boards. In the meantime, users of 'Rev B' boards can select/deselect the external AREF using the respective line of code:
OutputPort arefSelect = new OutputPort((Cpu.Pin)56, false); // use external aref OutputPort arefSelect = new OutputPort((Cpu.Pin)56, true); // use internal arefThis code will have no effect on 'Rev A' boards.
Chris
P.S. Netduino 'Rev B' boards are en route to authorized resellers around the world. Most resellers should have 'Rev B' boards in stock by the end of next week.
