In SX Microcontrollers, SX/B Compiler and SX-Key Tool, robotworkshop wrote:

From the specs it sounds more like Mark is using two voltage regulator because he wants two different voltages (8.5v and 5v).  It might simplify things a bit to use a Serial driver like a MAX232 and just use a single 5v regulator for the project.  I haven't seen any mention of the actual current used by the project and although running the SX at 75Mhz is supposed to take a bit more current it may not be an issue at all for this particular project.  I don't see where 220ma should be too much for an LM2940.  For sizing the voltage regulator required you'll also have to factor in all the other parts on the board that also use the 5V supply.  The idea of using a diode to drop the voltage a bit before it goes into the voltage regulator isn't a bad idea at all (as long as it is sized to handle the current) since it offers the added benefit of reverse polarity protection.  If you connect the power backwards you won't fry it!

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