I have an interesting problem in building something with robotics. I am using a PIC16F877A micro-controller to control the robot. The motors of the robot require 6 volts and the PIC requires 5 volts. I was wondering if there was an easy way to get both of these required voltages from a common voltage source. The motors suggest running on 4 AA batteries, and I was going to just use a 7805 voltage regulator to than reduce the voltage to 5 volts, but the regulator requires at least 7 volts to function correctly. I also thought that I could use a voltage divider network, but none seemed to be convenient.
Answer
Chris Stratton's solution is the best, I think.
Get a 3.3V LDO. The PIC16F877A (datasheet) will run happily from 3.3V, as will most of the usual transistorised H-bridges that you might use for motor drive. You can then run the whole thing from 4 AA cells, either alkaline or NiMH rechargeables. This avoids problems when the battery terminal voltage drops under load (which it will once you turn on the motors).
It is not a good idea to run the motors and the PIC from the same power supply with no intermediate filtering or regulation, as the noise may cause the PIC to reset.
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