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By RobRob
SparkFun Serial Basic Breakout - CH340G

Is is ok to have an external power source connected while using the Serial Basic? I'm using a breadboarded Arduino (atmega328) with 5V supplied by LM7805 regulator with smoothing caps and protection diode and resettable fuse.

Can I just not connect VCC and GND on the Serial Basic?

If it is ok, are there any other things I need to consider?

Thanks, Robby R.
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By chipace
If your ch340g is configured for 5V operation (by default it is 3.3v, you would need to cut a trace and solder 2 pads) then there is no issue with 5.0v external power being present. Just don't use that modified ch340g to connect to a 3.3V part later (you will damage the 3.3v part).
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By TS-Mark
Hi RobRob,

Chipace is correct here. One other thing you will want to do if you are using an external power supply with the Serial Basic is to create a common ground between the Serial Basic and the rest of your circuit by connecting the GND pin on your Serial Basic to your ground in the circuit. Without that, your serial communication is going to be erratic since it does not have a reference voltage. Just leave 5V/Vcc unconnected so you don't send 5V back into your USB from the external supply.