Microcontroller power supply problem
Use an LDO regulator rather than a resistive divider. For example, the Microchip MIC5504-3.3YM5. All you need is one tiny part and two small 1uF ceramic capacitors. 



The resistive divider will cause unstable voltage when the MCU draws different currents, and it wastes power. 

This part (and there are many other choices, this is just a particular inexpensive option) will accept up to 5.5V in and supply 3.3V out even if the output current is relatively large. 

Inspired by @ChrisStratton, here is one way to think of how a linear LDO works (with apologies to Winfield Hill et al.) 



"Regulator man" adjusts the pot to maintain the output voltage at 3.3V. If the load is heavy the pot gets turned to a low resistance, if there is little load then the pot gets turned to a very high resistance. All Regulator Man can do is turn the pot to almost zero resistance so the output voltage can never quite reach the input voltage. Iq is just a bit of current the regulator needs to work.