Joined: Sun May 05, 2002 22:05 Posts: 2063 Location: Lappeenranta, Finland
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74LCX245 is there to convert the +5v levels of the parallel port data pins to +3.3v level as the PCD8544 controller isn't meant to take +5v to it's input pins. +3.3v because of the LP2950 3.3v regulator that is used to power the 74LCX245 and the lcd. So using external power source doesn't change anything. But the circuit might work just fine without the 74LCX245 anyway but I'm not promising anything.
If you're using external power source you can just leave the lpt pin 7 not connected. Or you could use it to switch the external power supply.
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