Hello.
Plugging your 2 AA batteries directly in to the 3V3 should be OK as long as you do one of the following:
- Never connect USB or VIN at the same as the battery. To reprogram your Wixel, you would have to disconnect the battery, connect USB, program, disconnect USB, then reconnect the battery.
OR
- Sever the output pin of the 3.3 V regulator by cutting pin 5, the lower left pin of the regulator if the USB connector is facing up. Then you won’t be able to power the Wixel from VIN or USB, but it will be safe to have VIN and/or USB connected at the same as the batteries. This is the way to go if you eventually want your system to be very low power.
The reason for this is that you want to avoid powering the 3.3 V regulator and connecting its output directly to batteries. The batteries would have a voltage lower than 3.3 V so the regulator would be unable to get the voltage up to 3.3 V, and it could break itself or get very hot trying.
–David